Perhaps the most important question we can possible ask is, “are we alone in the Universe?”.
And so far, the answer has been, “I don’t know”. I mean, it’s a huge Universe, with hundreds of billions of stars in the Milky Way, and now we learn there are trillions of galaxies in the Universe.
Is there life closer to home? What about in the Solar System? There are a few existing places we could look for life close to home. Really any place in the Solar System where there’s liquid water. Wherever we find water on Earth, we find life, so it make sense to search for places with liquid water in the Solar System.
I know, I know, life could take all kinds of wonderful forms. Enlightened beings of pure energy, living among us right now. Or maybe space whales on Titan that swim through lakes of ammonia. Beep boop silicon robot lifeforms that calculate the wasted potential of our lives.
Sure, we could search for those things, and we will. Later. We haven’t even got this basic problem done yet. Earth water life? Check! Other water life? No idea.
It turns out, water’s everywhere in the Solar System. In comets and asteroids, on the icy moons of Jupiter and Saturn, especially Europa or Enceladus. Or you could look for life on Mars.
Sloping buttes and layered outcrops within the “Murray formation” layer of lower Mount Sharp. Credit: NASA
Mars is similar to Earth in many ways, however, it’s smaller, has less gravity, a thinner atmosphere. And unfortunately, it’s bone dry. There are vast polar caps of water ice, but they’re frozen solid. There appears to be briny liquid water underneath the surface, and it occasionally spurts out onto the surface. Because it’s close and relatively easy to explore, it’s been the place scientists have gone looking for past or current life.
Researchers tried to answer the question with NASA’s twin Viking Landers, which touched down in 1976. The landers were both equipped with three biology experiments. The researchers weren’t kidding around, they were going to nail this question: is there life on Mars?
In the first experiment, they took soil samples from Mars, mixed in a liquid solution with organic and inorganic compounds, and then measured what chemicals were released. In a second experiment, they put Earth organic compounds into Martian soil, and saw carbon dioxide released. In the third experiment, they heated Martian soil and saw organic material come out of the soil.
The landing site of Viking 1 on Mars in 1977, with trenches dug in the soil for the biology experiments. Credit: NASA/JPL
Three experiments, and stuff happened in all three. Stuff! Pretty exciting, right? Unfortunately, there were equally plausible non-biological explanations for each of the results. The astrobiology community wasn’t convinced, and they still fight in brutal cage matches to this day. It was ambitious, but inconclusive. The worst kind of conclusive.
Researchers found more inconclusive evidence in 1994. Ugh, there’s that word again. They were studying a meteorite that fell in Antarctica, but came from Mars, based on gas samples taken from inside the rock.
They thought they found evidence of fossilized bacterial life inside the meteorite. But again, there were too many explanations for how the life could have gotten in there from here on Earth. Life found a way… to burrow into a rock from Mars.
NASA learned a powerful lesson from this experience. If they were going to prove life on Mars, they had to go about it carefully and conclusively, building up evidence that had no controversy.
Artist Concept, Mars Exploration Rovers. NASA/JPL-Caltech
The Spirit and Opportunity Rovers were an example of building up this case cautiously. They were sent to Mars in 2004 to find evidence of water. Not water today, but water in the ancient past. Old water Over the course of several years of exploration, both rovers turned up multiple lines of evidence there was water on the surface of Mars in the ancient past.
They found concretions, tiny pebbles containing iron-rich hematite that forms on Earth in water. They found the mineral gypsum; again, something that’s deposited by water on Earth.
A bright mineral vein informally named Homestake. The vein is about the width of a thumb and about 18 inches (45 centimeters) long. Opportunity examined it in November 2011 (Sol 2763) and found it to be rich in calcium and sulfur, possibly the calcium-sulfate mineral gypsum. Credit: NASA/JPL-Caltech
NASA’s Curiosity Rover took this analysis to the next level, arriving in 2012 and searching for evidence that water was on Mars for vast periods of time; long enough for Martian life to evolve.
Once again, Curiosity found multiple lines of evidence that water acted on the surface of Mars. It found an ancient streambed near its landing site, and drilled into rock that showed the region was habitable for long periods of time.
In 2014, NASA turned the focus of its rovers from looking for evidence of water to searching for past evidence of life.
Curiosity found one of the most interesting targets: a strange strange rock formations while it was passing through an ancient riverbed on Mars. While it was examining the Gillespie Lake outcrop in Yellowknife Bay, it photographed sedimentary rock that looks very similar to deposits we see here on Earth. They’re caused by the fossilized mats of bacteria colonies that lived billions of years ago.
A bright and interestingly shaped tiny pebble shows up among the soil on a rock, called “Gillespie Lake,” which was imaged by Curiosity’s Mars Hand Lens Imager on Dec. 19, 2012, the 132nd sol, or Martian day of Curiosity’s mission on Mars. Credit: NASA / JPL-Caltech / MSSS.
Not life today, but life when Mars was warmer and wetter. Still, fossilized life on Mars is better than no life at all. But there might still be life on Mars, right now, today. The best evidence is not on its surface, but in its atmosphere. Several spacecraft have detected trace amounts of methane in the Martian atmosphere.
Methane is a chemical that breaks down quickly in sunlight. If you farted on Mars, the methane from your farts would dissipate in a few hundred years. If spacecraft have detected this methane in the atmosphere, that means there’s some source replenishing those sneaky squeakers. It could be volcanic activity, but it might also be life. There could be microbes hanging on, in the last few places with liquid water, producing methane as a byproduct.
The European ExoMars orbiter just arrived at Mars, and its main job is sniff the Martian atmosphere and get to the bottom of this question.
Are there trace elements mixed in with the methane that means its volcanic in origin? Or did life create it? And if there’s life, where is it located? ExoMars should help us target a location for future study.
The European/Russian ExoMars Trace Gas Orbiter (TGO) will sniff the Martian atmosphere for signs of methane which could originate for either biological or geological mechanisms. Credit: ESA
NASA is following up Curiosity with a twin rover designed to search for life. The Mars 2020 Rover will be a mobile astrobiology laboratory, capable of scooping up material from the surface of Mars and digesting it, scientifically speaking. It’ll search for the chemicals and structures produced by past life on Mars. It’ll also collect samples for a future sample return mission.
Even if we do discover if there’s life on Mars, it’s entirely possible that we and Martian life are actually related by a common ancestor, that split off billions of years ago. In fact, some astrobiologists think that Mars is a better place for life to have gotten started.
Not the dry husk of a Red Planet that we know today, but a much wetter, warmer version that we now know existed billions of years ago. When the surface of Mars was warm enough for liquid water to form oceans, lakes and rivers. And we now know it was like this for millions of years.
A conception of an ancient Mars, flush with oceans, clouds and life. Credit: Kevin Gill.
While Earth was still reeling from an early impact by the massive planet that crashed into it, forming the Moon, life on Mars could have gotten started early.
But how could we actually be related? The idea of Panspermia says that life could travel naturally from world to world in the Solar System, purely through the asteroid strikes that were regularly pounding everything in the early days.
Imagine an asteroid smashing into a world like Mars. In the lower gravity of Mars, debris from the impact could be launched into an escape trajectory, free to travel through the Solar System.
We know that bacteria can survive almost indefinitely, freeze dried, and protected from radiation within chunks of space rock. So it’s possible they could make the journey from Mars to Earth, crossing the orbit of our planet.
Even more amazingly, the meteorites that enter the Earth’s atmosphere would protect some of the bacterial inhabitants inside. As the Earth’s atmosphere is thick enough to slow down the descent of the space rocks, the tiny bacterialnauts could survive the entire journey from Mars, through space, to Earth.
Credit: NASA/JPL-Caltech
If we do find life on Mars, how will we know it’s actually related to us? If Martian life has the similar DNA structure to Earth life, it’s probably related. In fact, we could probably trace the life back to determine the common ancestor, and even figure out when the tiny lifeforms make the journey.
If we do find life on Mars, which is related to us, that just means that life got around the Solar System. It doesn’t help us answer the bigger question about whether there’s life in the larger Universe. In fact, until we actually get a probe out to nearby stars, or receive signals from them, we might never know.
An even more amazing possibility is that it’s not related. That life on Mars arose completely independently. One clue that scientists will be looking for is the way the Martian life’s instructions are encoded. Here on Earth, all life follows “left-handed chirality” for the amino acid building blocks that make up DNA and RNA. But if right-handed amino acids are being used by Martian life, that would mean a completely independent origin of life.
Of course, if the life doesn’t use amino acids or DNA at all, then all bets are off. It’ll be truly alien, using a chemistry that we don’t understand at all.
There are many who believe that Mars isn’t the best place in the Solar System to search for life, that there are other places, like Europa or Enceladus, where there’s a vast amount of liquid water to be explored.
But Mars is close, it’s got a surface you can land on. We know there’s liquid water beneath the surface, and there was water there for a long time in the past. We’ve got the rovers, orbiters and landers on the planet and in the works to get to the bottom of this question. It’s an exciting time to be part of this search.
Image of the Messier 27 planetary nebula, taken by NASA's Spitzer Space Telescope. Credit: NASA/JPL-Caltech/J. Hora (Harvard-Smithsonian CfA)
Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the famous and easily-spotted Dumbbell Nebula. Enjoy!
Back in the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list would come to include 100 of the most fabulous objects in the night sky.
Known today as the Messier Catalog, this work has come to be viewed as one of the most important milestones in the study of Deep Space Objects. One of these is the famed Dumbbell Nebula – also known as Messier 27, the Apple Core Nebula, and NGC 6853. Because it of its brightness, it is easily viewed with binoculars and amateur telescopes, and was the first planetary Nebula to be discovered by Charles Messier.
Description:
This bright planetary nebula is located in the direction of the Vulpecula constellation, at a distance of about 1,360 light years from Earth. Located within the equatorial plane, this nebula is essentially a dying star that has been ejecting a shell of hot gas into space for roughly 48,000 years.
Picture of M27 processed and combined using IRAF and MaxIm DL. Credit: Wikipedia Commons/Mohamad Abbas
The star responsible is an extremely hot blueish subdwarf star, which emits primarily highly energetic radiation in the non-visible part of the electromagnetic spectrum. This energy is absorbed by exciting the nebula’s gas, and then re-emitted by the nebula. Messier 27 particular green glow (hence the nickname “Apple Core Nebula”) is due to the presence of doubly-ionized oxygen in its center, which emits green light at 5007 Angstroms.
For many years I quested to understand the distant and mysterious M27, but no one could answer my questions. I researched it, and learned that it was made up of doubly ionized oxygen. I had hoped that perhaps there was a spectral reason to what I viewed year after year – but still no answer.
Like all amateurs, I became the victim of “aperture fever” and I continued to study M27 with a 12″ telescope, never realizing the answer was right there – I just hadn’t powered up enough. Several years later while studying at the Observatory, I was viewing through a friend’s identical 12″ telescope and, as chance would have it, he was using about twice the magnification that I normally used on the “Dumbbell.”
Imagine my total astonishment as I realized for the very first time that the faint central star had an even fainter companion that made it seem to wink! At smaller apertures or low power, this was not revealed. Still, the eye could “see” a movement within the nebula – the central, radiating star and its companion.
Image from a ground-based telescope at Westview Observatory in Cridersville, OH. Credit: Wikipedia Commons/Charlemagne920
“As the gas at the inner edge begins to ionize, the pressure throughout the nebula is equalized by a shock which moves outward through the neutral gas. Later, when about 1/10 of the nebular mass is ionized, a second shock is released from the ionized front, and this shock moves through the neutral shell reaching the outer edge. The density of the HI gas just behind the shock is quite large and the outward gas velocity increases within until it reaches a maximum of 40-80 km per second just behind the shock front. The projected appearance of the nebula during this stage has a double ring structure similar to many observed planetaries.”
But, movement or no movement, Messier 27 is known as one of the top “polluters” of the interstellar medium. As Joseph L. Hora ( et al.) of the Harvard-Smithsonian Center for Astrophysics said in his 2008 study “Planetary Nebulae: Exposing the Top Polluters of the ISM“:
“The high mass loss rates of stars in their asymptotic giant branch (AGB) stage of evolution is one of the most important pathways for mass return from stars to the ISM. In the planetary nebulae (PNe) phase, the ejected material is illuminated and can be altered by the UV radiation from the central star. PNe therefore play a significant role in the ISM recycling process and in changing the environment around them…
“A key link in the recycling of material to the Interstellar Medium (ISM) is the phase of stellar evolution from Asymptotic Giant Branch (AGB) to white dwarf star. When stars are on the AGB, they begin to lose mass at a prodigious rate. The stars on the AGB are relatively cool, and their atmospheres are a fertile environment for the formation of dust and molecules. The material can include molecular hydrogen (H2), silicates, and carbon-rich dust. The star is fouling its immediate neighborhood with these noxious emissions. The star is burning clean hydrogen fuel, but unlike a “green” hydrogen vehicle that outputs nothing except water, the star produces ejecta of various types, some of which have properties similar to that of soot from a gas-burning automobile. A significant fraction of the material returned to the ISM goes through the AGB – PNe pathway, making these stars one of the major sources of pollution of the ISM.
“However, these stars are not done with their stellar ejecta yet. Before the slow, massive AGB wind can escape, the star begins a rapid evolution where it contracts and its surface temperature increases. The star starts ejecting a less massive but high velocity wind that crashes into the existing circumstellar material, which can create a shock and a higher density shell. As the stellar temperature increases, the UV flux increases and it ionizes the gas surrounding the central star, and can excite emission from molecules, heat the dust, and even begin to break apart the molecules and dust grains. The objects are then visible as planetary nebulae, exposing their long history of spewing material into the ISM, and further processing the ejecta. There are even reports that the central stars of some PNe may be engaging in nucleosynthesis for purposes of self-enrichment, which can be traced by monitoring the elemental abundances in the nebulae. Clearly, we must assess and understand the processes going on in these objects in order to understand their impact on the ISM, and their influence on future generations of stars.”
Messier 27 and the Summer Triangle. Credit: Wikisky
History of Observation:
So, chances are on July 12th, 1764, when Charles Messier discovered this new and fascinating class of objects, he didn’t really have a clue as to how important his observation would be. From his notes of that night, he reports:
“I have worked on the research of the nebulae, and I have discovered one in the constellation Vulpecula, between the two forepaws, and very near the star of fifth magnitude, the fourteenth of that constellation, according to the catalog of Flamsteed: One sees it well in an ordinary refractor of three feet and a half. I have examined it with a Gregorian telescope which magnified 104 times: it appears in an oval shape; it doesn’t contain any star; its diameter is about 4 minutes of arc. I have compared that nebula with the neighboring star which I have mentioned above [14 Vul]; its right ascension has been concluded at 297d 21′ 41″, and its declination 22d 4′ 0″ north.”
Of course, Sir William Herschel’s own curiosity would get the better of him and although he would never publish his own findings on an object previously cataloged by Messier, he did keep his own private notes. Here is an excerpt from just one of his many observations:
“1782, Sept. 30. My sister discovered this nebula this evening in sweeping for comets; on comparing its place with Messier’s nebulae we find it is his 27. It is very curious with a compound piece; the shape of it though oval as M. [Messier] calls it, is rather divided in two; it is situated among a number of small [faint] stars, but with this compound piece no star is visible in it. I can only make it bear 278. It vanishes with higher powers on account of its feeble light. With 278 the division between the two patches is stronger, because the intermediate faint light vanishes more.”
So where did Messier 27 get its famous moniker? From Sir John Herschel, who wrote: “A most extraordinary object; very bright; an unresolved nebula, shaped something like an hour-glass, filled into an oval outline with a much less dense nebulosity. The central mass may be compared to a vertebra or a dumb-bell. The southern head is denser than the northern. One or two stars seen in it.”
It would be several years, and several more historical astronomers, before the true nature of Messier 27 would even be hinted at. At one level, they understood it to be a nebula – but it wasn’t until 1864 when William Huggins came along and began to decode the mystery:
“It is obvious that the nebulae 37 H IV (NGC 3242), Struve 6 (NGC 6572), 73 H IV (NGC 6826), 1 H IV (NGC 7009), 57 M, 18 H. IV (NGC 7662) and 27 M. can no longer be regarded as aggregations of suns after the order to which our own sun and the fixed stars belong. We have with these objects to do no longer with a special modification only of our own type of suns, but find ourselves in the presence of objects possessing a distinct and peculiar plan of structure. In place of an incandescent solid or liquid body transmitting light of all refrangibilities through an atmosphere which intercepts by absorption a certain number of them, such as our sun appears to be, we must probably regard these objects, or at least their photo-surfaces, as enormous masses of luminous gas or vapour. For it is alone from matter in the gaseous state that light consisting of certain definite refrangibilities only, as is the case with the light of these nebulae, is known to be emitted.”
Whether or not you enjoy M27 as one of the most superb planetary nebula in the night sky (or as a science object) you will 100% agree with the words of of Burnham: “The observer who spends a few moments in quiet contemplation of this nebula will be made aware of direct contact with cosmic things; even the radiation reaching us from the celestial depths is of a type unknown on Earth…”
Locating Messier 27:
When you first begin, Messier 27 will seem like such an elusive target – but with a few simple sky “tricks”, it won’t be long until you’ll be finding this spectacular planetary nebula under just about any sky conditions. The hardest part is simply sorting out all the stars in the area to know the right ones to aim at!
The way I found easiest to teach others was to start BIG. The cruciform patterns of the Cygnus and Aquila constellations are easy to recognize and can be seen from even urban locations. Once you’ve identified these two constellations, you’re going smaller by locating Lyra and the tiny kite-shape of Delphinus.
Now you’ve circled the area and the hunt for Vulpecula the Fox begins! What’s that you say? You can’t distinguish Vulpecula’s primary stars from the rest of the field? You’re right. They don’t stand out like they should, and being tempted to simply aim halfway between Albeireo (Beta Cygni) and Alpha Delphini is too much of a span to be accurate. So what are we going to do? Here’s where some patience comes into play.
If you give yourself time, you’ll begin to notice the stars of Sagitta are ever so slightly brighter than the rest of the field stars around it, and it won’t be long until you pick out that arrow pattern. In your mind, measure the distance between Delta and Gamma (the 8 and Y shape on a starfinder map) and then just aim your binoculars or finderscope exactly that same distance due north of Gamma.
The location of M27 in the constellation Vulpecula. Credit: IAU/Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)
You’ll find M27 every time! In average binoculars it will appear as a fuzzy, out of focus large star in a stellar field. In the finderscope, it may not appear at all… But in a telescope? Be prepared to be blown away! And here are the quick facts on the Dumbbell Nebula to help get you started:
Object Name: Messier 27 Alternative Designations: M27, NGC 6853, The Dumbbell Nebula Object Type: Planetary Nebula Constellation: Vulpecula Right Ascension: 19 : 59.6 (h:m) Declination: +22 : 43 (deg:m) Distance: 1.25 (kly) Visual Brightness: 7.4 (mag) Apparent Dimension: 8.0×5.7 (arc min)
Image taken by the Viking 1 orbiter in June 1976, showing Mars thin atmosphere and dusty, red surface. Credits: NASA/Viking 1
Human exploration of Mars has been ramping up in the past few decades. In addition to the eight active missions on or around the Red Planet, seven more robotic landers, rovers and orbiters are scheduled to be deployed there by the end of the decade. And by the 2030s and after, several space agencies are planning to mount crewed missions to the surface as well.
On top of that, there are even plenty of volunteers who are prepared to make a one-way journey to Mars, and people advocating that we turn it into a second home. All of these proposals have focused attention on the peculiar hazards that come with sending human beings to Mars. Aside from its cold, dry environment, lack of air, and huge sandstorms, there’s also the matter of its radiation.
Causes:
Mars has no protective magnetosphere, as Earth does. Scientists believe that at one time, Mars also experienced convection currents in its core, creating a dynamo effect that powered a planetary magnetic field. However, roughly 4.2 billions year ago – either due to a massive impact from a large object, or rapid cooling in its core – this dynamo effect ceased.
Artist’s rendering of a solar storm hitting Mars and stripping ions from the planet’s upper atmosphere. Credits: NASA/GSFC
As a result, over the course of the next 500 million years, Mars atmosphere was slowly stripped away by solar wind. Between the loss of its magnetic field and its atmosphere, the surface of Mars is exposed to much higher levels of radiation than Earth. And in addition to regular exposure to cosmic rays and solar wind, it receives occasional lethal blasts that occur with strong solar flares.
Investigations:
NASA’s 2001 Mars Odyssey spacecraft was equipped with a special instrument called the Martian Radiation Experiment (or MARIE), which was designed to measure the radiation environment around Mars. Since Mars has such a thin atmosphere, radiation detected by Mars Odyssey would be roughly the same as on the surface.
Over the course of about 18 months, the Mars Odyssey probe detected ongoing radiation levels which are 2.5 times higher than what astronauts experience on the International Space Station – 22 millirads per day, which works out to 8000 millirads (8 rads) per year. The spacecraft also detected 2 solar proton events, where radiation levels peaked at about 2,000 millirads in a day, and a few other events that got up to about 100 millirads.
For comparison, human beings in developed nations are exposed to (on average) 0.62 rads per year. And while studies have shown that the human body can withstand a dose of up to 200 rads without permanent damage, prolonged exposure to the kinds of levels detected on Mars could lead to all kinds of health problems – like acute radiation sickness, increased risk of cancer, genetic damage, and even death.
Diagram showing the amount of cosmic radiation the surface of Mars is exposed to. Credit: NASA
And given that exposure to any amount of radiation carries with it some degree of risk, NASA and other space agencies maintain a strict policy of ALARA (As-Low-As-Reasonable-Achievable) when planning missions.
Possible Solutions:
Human explorers to Mars will definitely need to deal with the increased radiation levels on the surface. What’s more, any attempts to colonize the Red Planet will also require measures to ensure that exposure to radiation is minimized. Already, several solutions – both short term and long- have been proposed to address this problem.
For example, NASA maintains multiple satellites that study the Sun, the space environment throughout the Solar System, and monitor for galactic cosmic rays (GCRs), in the hopes of gaining a better understanding of solar and cosmic radiation. They’ve also been looking for ways to develop better shielding for astronauts and electronics.
In 2014, NASA launched the Reducing Galactic Cosmic Rays Challenge, an incentive-based competition that awarded a total of $12,000 to ideas on how to reduce astronauts’ exposure to galactic cosmic rays. After the initial challenge in April of 2014, a follow-up challenge took place in July that awarded a prize of $30,000 for ideas involving active and passive protection.
When it comes to long-term stays and colonization, several more ideas have been floated in the past. For instance, as Robert Zubrin and David Baker explained in their proposal for a low-cast “Mars Direct” mission, habitats built directly into the ground would be naturally shielded against radiation. Zubrin expanded on this in his 1996 bookThe Case for Mars: The Plan to Settle the Red Planet and Why We Must.
Proposals have also been made to build habitats above-ground using inflatable modules encased in ceramics created using Martian soil. Similar to what has been proposed by both NASA and the ESA for a settlement on the Moon, this plan would rely heavily on robots using 3D printing technique known as “sintering“, where sand is turned into a molten material using x-rays.
MarsOne, the non-profit organization dedicated to colonizing Mars in the coming decades, also has proposals for how to shield Martian settlers. Addressing the issue of radiation, the organization has proposed building shielding into the mission’s spacecraft, transit vehicle, and habitation module. In the event of a solar flare, where this protection is insufficient, they advocate creating a dedicated radiation shelter (located in a hollow water tank) inside their Mars Transit Habitat.
But perhaps the most radical proposal for reducing Mars’ exposure to harmful radiation involves jump-starting the planet’s core to restore its magnetosphere. To do this, we would need to liquefy the planet’s outer core so that it can convect around the inner core once again. The planet’s own rotation would begin to create a dynamo effect, and a magnetic field would be generated.
Artist impression of a Mars settlement with cutaway view. Credit: NASA Ames Research Center
According to Sam Factor, a graduate student with the Department of Astronomy at the University of Texas, there are two ways to do this. The first would be to detonate a series of thermonuclear warheads near the planet’s core, while the second involves running an electric current through the planet, producing resistance at the core which would heat it up.
In addition, a 2008 study conducted by researchers from the National Institute for Fusion Science (NIFS) in Japan addressed the possibility of creating an artificial magnetic field around Earth. After considering continuous measurements that indicated a 10% drop in intensity in the past 150 years, they went on to advocate how a series of planet-encircling superconducting rings could compensate for future losses.
With some adjustments, such a system could be adapted for Mars, creating an artificial magnetic field that could help shield the surface from some of the harmful radiation it regularly receives. In the event that terraformers attempt to create an atmosphere for Mars, this system could also ensure that it is protected from solar wind.
Lastly, a study in 2007 by researchers from the Institute for Mineralogy and Petrology in Switzerland and the Faculty of Earth and Life Sciences at Vrije University in Amsterdam managed to replicate what Mars’ core looks like. Using a diamond chamber, the team was able to replicate pressure conditions on iron-sulfur and iron-nickel-sulfur systems that correspond to the center of Mars.
What they found was that at the temperatures expected in the Martian core (~1500 K, or 1227 °C; 2240 °F), the inner core would be liquid, but some solidification would occur in the outer core. This is quite different from Earth’s core, where the solidification of the inner core releases heat that keeps the outer core molten, thus creating the dynamo effect that powers our magnetic field.
The absence of a solid inner core on Mars would mean that the once-liquid outer core must have had a different energy source. Naturally, that heat source has since failed, causing the outer core to solidify, thus arresting any dynamo effect. However, their research also showed that planetary cooling could lead to core solidification in the future, either due to iron-rich solids sinking towards the center or iron-sulfides crystallizing in the core.
In other words, Mars’ core might become solid someday, which would heat the outer core and turn it molten. Combined with the planet’s own rotation, this would generate the dynamo effect that would once again fire up the planet’s magnetic field. If this is true, then colonizing Mars and living there safely could be a simple matter of waiting for the core to crystallize.
There’s no way around it. At present, the radiation on the surface of Mars is pretty hazardous! Therefore, any crewed missions to the planet in the future will need to take into account radiation shielding and counter-measures. And any long-term stays there – at least for the foreseeable future – are going to have to be built into the ground, or hardened against solar and cosmic rays.
Approximate true-color rendering of the central part of the “Columbia Hills”, taken by NASA’s Mars Exploration Rover Spirit panoramic camera. Credit: NASA/JPL
But you know what they say about necessity being the mother of invention, right? And with such luminaries as Stephen Hawking saying that we need to start colonizing other worlds in order to survive as a species, and people like Elon Musk and Bas Lansdrop looking to make it happen, we’re sure to see some very inventive solutions in the coming generations!
If you want, learn more about the MARIE instrument on board NASA’s Mars Odyssey spacecraft, and the radiation risks humans will face trying to go to Mars.
Okay, so this article is Colonizing the Outer Solar System, and is actually part 2 of our team up with Fraser Cain of Universe Today, who looked at colonizing the inner solar system. You might want jump over there now and watch that part first, if you are coming in from having seen part 1, welcome, it is great having you here.
Without further ado let us get started. There is no official demarcation between the inner and outer solar system but for today we will be beginning the outer solar system at the Asteroid Belt.
Artist concept of the asteroid belt. Credit: NASA
The Asteroid Belt is always of interest to us for colonization. We have talked about mining them before if you want the details on that but for today I’ll just remind everyone that there are very rich in metals, including precious metals like gold and platinum, and that provides all the motivation we need to colonize them. We have a lot of places to cover so we won’t repeat the details on that today.
You cannot terraform asteroids the way you could Venus or Mars so that you could walk around on them like Earth, but in every respect they have a lot going for them as a candidate. They’ve got plenty for rock and metal for construction, they have lots of the basic organic elements, and they even have some water. They also get a decent amount of sunlight, less than Mars let alone Earth, but still enough for use as a power source and to grow plants.
But they don’t have much gravity, which – pardon the pun – has its ups and downs. There just isn’t much mass in the Belt. The entire thing has only a small fraction of the mass of our moon, and over half of that is in the four biggest asteroids, essentially dwarf planets in their own right. The remainder is scattered over millions of asteroids. Even the biggest, Ceres, is only about 1% of 1% of Earth’s mass, has a surface gravity of 3% Earth-normal, and an escape velocity low enough most model rockets could get into orbit. And again, it is the biggest, most you could get away from by jumping hard and if you dropped an object on one it might take a few minutes to land.
Don’t blink… an artist’s conception of an asteroid blocking out a distant star. Image credit: NASA.
You can still terraform one though, by definition too. The gentleman who coined the term, science fiction author Jack Williamson, who also coined the term genetic engineering, used it for a smaller asteroid just a few kilometers across, so any definition of terraforming has to include tiny asteroids too.
Of course in that story it’s like a small planet because they had artificial gravity, we don’t, if we want to fake gravity without having mass we need to spin stuff around. So if we want to terraform an asteroid we need to hollow it out and fill it with air and spin it around.
Of course you do not actually hollow out the asteroid and spin it, asteroids are loose balls of gravel and most would fly apart given any noticeable spin. Instead you would hollow it out and set a cylinder spinning inside it. Sort of like how a good thermos has an outside container and inside one with a layer of vacuum in between, we would spin the inner cylinder.
You wouldn’t have to work hard to hollow out an asteroid either, most aren’t big enough to have sufficient gravity and pressure to crush an empty beer can even at their center. So you can pull matter out from them very easily and shore up the sides with very thin metal walls or even ice. Or just have your cylinder set inside a second non-spinning outer skin or superstructure, like your washer or dryer.
You can then conduct your mining from the inside, shielded from space. You could ever pressurize that hollowed out area if your spinning living area was inside its own superstructure. No gravity, but warmth and air, and you could get away with just a little spin without tearing it apart, maybe enough for plants to grow to normally.
It should be noted that you can potentially colonize even the gas giants themselves, even though our focus today is mostly on their moons. That requires a lot more effort and technology then the sorts of colonies we are discussing today, Fraser and I decided to keep things near-future and fairly low tech, though he actually did an article on colonizing Jupiter itself last year that was my main source material back before got to talking and decided to do a video together.
Jupiter with Io and Ganymede taken by amateur astronomer Damian Peach. Credit: NASA / Damian Peach
Hydrogen is plentiful on Jupiter itself and floating refineries or ships that fly down to scoop it up might be quite useful, but again today we are more interested in its moons. The biggest problem with colonizing the moons of Jupiter is all the radiation the planet gives off.
Europa is best known as a place where the surface is covered with ice but beneath it is thought to be a vast subsurface ocean. It is the sixth largest moon coming right behind our own at number five and is one of the original four moons Galileo discovered back in 1610, almost two centuries before we even discovered Uranus, so it has always been a source of interest. However as we have discovered more planets and moons we have come to believe quite a few of them might also have subsurface oceans too.
Now what is neat about them is that water, liquid water, always leaves the door open to the possibility of life already existing there. We still know so little about how life originally evolved and what conditions permit that to occur that we cannot rule out places like Europa already having their own plants and animals swimming around under that ice.
They probably do not and obviously we wouldn’t want to colonize them, beyond research bases, if they did, but if they do not they become excellent places to colonize. You could have submarine cities in such places floating around in the sea or those buried in the surface ice layer, well shielded from radiation and debris. The water also geysers up to the surface in some places so you can start off near those, you don’t have to drill down through kilometers of ice on day one.
Water, and hydrogen, are also quite uncommon in the inner solar system so having access to a place like Europa where the escape velocity is only about a fifth of our own is quite handy for export. Now as we move on to talk about moons a lot it is important to note that when I say something has a fifth of the escape velocity of Earth that doesn’t mean it is fives time easier to get off of. Energy rises with the square of velocity so if you need to go five times faster you need to spend 5-squared or 25 times more energy, and even more if that place has tons of air creating friction and drag, atmospheres are hard to claw your way up through though they make landing easier too. But even ignoring air friction you can move 25 liters of water off of Europa for every liter you could export from Earth and even it is a very high in gravity compared to most moons and comets. Plus we probably don’t want to export lots of water, or anything else, off of Earth anyway.
Artist’s concept of Trojan asteroids, small bodies that dominate our solar system. Credit: NASA
We should start by noting two things. First, the Asteroid Belt is not the only place you find asteroids, Jupiter’s Trojan Asteroids are nearly as numerous, and every planet, including Earth, has an equivalent to Jupiter’s Trojan Asteroids at its own Lagrange Points with the Sun. Though just as Jupiter dwarfs all the other planets so to does its collection of Lagrangian objects. They can quite big too, the largest 624 Hektor, is 400 km across, and has a size and shape similar to Pennsylvania.
And as these asteroids are at stable Lagrange Points, they orbit with Jupiter but always ahead and behind it, making transit to and from Jupiter much easier and making good waypoints.
Before we go out any further in the solar system we should probably address how you get the energy to stay alive. Mars is already quite cold compared to Earth, and the Asteroids and Jupiter even more so, but with thick insulation and some mirrors to bounce light in you can do fairly decently. Indeed, sunlight out by Jupiter is already down to just 4% of what Earth gets, meaning at Jovian distances it is about 50 W/m²
That might not sound like much but it is actually almost a third of what average illumination is on Earth, when you factor in atmospheric reflection, cloudy days, nighttime, and higher, colder latitudes. It is also a good deal brighter than the inside of most well-lit buildings, and is enough for decently robust photosynthesis to grow food. Especially with supplemental light from mirrors or LED growth lamps.
But once you get out to Saturn and further that becomes increasingly impractical and a serious issue, because while food growth does not show up on your electric bill it is what we use virtually all our energy for. Closer in to the sun we can use solar panels for power and we do not need any power to grow food. As we get further out we cannot use solar and we need to heat or cold habitats and supply lighting for food, so we need a lot more power even as our main source dries up.
So what are our options? Well the first is simple, build bigger mirrors. A mirror can be quite large and paper thin after all. Alternatively we can build those mirrors far away, closer to the sun, and and either focus them on the place we want illuminated or send an energy beam, microwaves perhaps or lasers, out to the destination to supply energy.
We also have the option of using fission, if we can find enough Uranium or Thorium. There is not a lot of either in the solar system, in the area of about one part per billion, but that does amount to hundreds of trillions of tons, and it should only take a few thousand tons a year to supply Earth’s entire electric grid. So we would be looking at millions of years worth of energy supply.
Of course fusion is even better, particularly since hydrogen becomes much more abundant as you get further from the Sun. We do not have fusion yet, but it is a technology we can plan around probably having inside our lifetimes, and while uranium and thorium might be counted in parts per billion, hydrogen is more plentiful than every other element combines, especially once you get far from the Sun and Inner Solar System.
So it is much better power source, an effectively unlimited one except on time scales of billions and trillion of years. Still, if we do not have it, we still have other options. Bigger mirrors, beaming energy outwards from closer to the Sun, and classic fission of Uranium and Thorium. Access to fusion is not absolutely necessary but if you have it you can unlock the outer solar system because you have your energy supply, a cheap and abundant fuel supply, and much faster and cheaper spaceships.
Of course hydrogen, plain old vanilla hydrogen with one proton, like the sun uses for fusion, is harder to fuse than deuterium and may be a lot longer developing, we also have fusion using Helium-3 which has some advantages over hydrogen, so that is worth keeping in mind as well as we proceed outward.
Since NASA’s Cassini spacecraft arrived at Saturn, the planet’s appearance has changed greatly. This view shows Saturn’s northern hemisphere in 2016, as that part of the planet nears its northern hemisphere summer solstice in May 2017. Image credit: NASA/JPL-Caltech/Space Science Institute.
Okay, let’s move on to Saturn, and again our focus is on its moons more than the planet itself. The biggest of those an the most interesting for colonization is Titan.
Titan is aptly named, this titanic moon contains more mass than than all of Saturn’s sixty or so other moons and by an entire order of magnitude at that. It is massive enough to hold an atmosphere, and one where the surface pressure is 45% higher than here on Earth. Even though Titan is much smaller than Earth, its atmosphere is about 20% more massive than our own. It’s almost all nitrogen too, even more than our own atmosphere, so while you would need a breather mask to supply oxygen and it is also super-cold, so you’d need a thick insulated suit, it doesn’t have to be a pressure suit like it would on Mars or almost anyplace else.
There’s no oxygen in the atmosphere, what little isn’t nitrogen is mostly methane and hydrogen, but there is plenty of oxygen in the ice on Titan which is quite abundant. So it has everything we need for life except energy and gravity. At 14% of earth normal it is probably too low for people to comfortably and safely adapt to, but we’ve already discussed ways of dealing with that. It is low enough that you could probably flap your arms and fly, if you had wing attached.
On the left is TALISE (Titan Lake In-situ Sampling Propelled Explorer), the ESA proposal. This would have it’s own propulsion, in the form of paddlewheels. Credit: bisbos.com
It needs some source of energy though, and we discussed that. Obviously if you’ve got fusion you have all the hydrogen you need, but Titan is one of those places we would probably want to colonize early on if we could, it is something you need a lot of to terraform other places, and is also rich in a lot of the others things we want. So we often think of it as a low-tech colony since it is one we would want early on.
In an scenario like that it is very easy to imagine a lot of local transit between Titan and its smaller neighboring moons, which are more rocky and might be easier to dig fissile materials like Uranium and Thorium out of. You might have a dozen or so small outposts on neighboring moons mining fissile materials and other metals and a big central hub on Titan they delivered that too which also exported Nitrogen to other colonies in the solar system.
Moving back and forth between moons is pretty easy, especially since things landing on Titan can aerobrake quite easily, whereas Titan itself has a pretty strong gravity well and thick atmosphere to climb out of but is a good candidate for a space elevator, since it requires nothing more sophisticated than a Lunar Elevator on our own moon and has an abundant supply of the materials needed to make Zylon for instance, a material strong enough to make an elevator there and which we can mass manufacture right now.
Titan might be the largest and most useful of Saturn’s moons, but again it isn’t the only one and not all of the other are just rocks for mining. At last count it has over sixty and many of them quite large. One of those, Enceladus, Saturn’s sixth largest moon, is a lot like Jupiter’s Moon Europa, in that we believe it has a large and thick subsurface ocean. So just like Europa it is an interesting candidate for Colonization. So Titan might be the hub for Saturn but it wouldn’t be the only significant place to colonize.
While Saturn is best known for its amazing rings, they tend to be overlooked in colonization. Now those rings are almost all ice and in total mass about a quarter as much as Enceladus, which again is Saturn’s Sixth largest moon, which is itself not even a thousandth of the Mass of Titan.
In spite of that the rings are not a bad place to set up shop. Being mostly water, they are abundant in hydrogen for fusion fuel and have little mass individually makes them as easy to approach or leave as an asteroid. Just big icebergs in space really, and there are many moonlets in the rings that can be as large as half a kilometer across. So you can burrow down inside one for protection from radiation and impacts and possibly mine smaller ones for their ice to be brought to places where water is not abundant.
In total those rings, which are all frozen water, only mass about 2% of Earth’s oceans, and about as much as the entire Antarctic sheet. So it is a lot of fresh water that is very easy to access and move elsewhere, and ice mines in the rings of Saturn might be quite useful and make good homes. Living inside an iceball might not sound appealing but it is better than it sounds like and we will discuss that more when we reach the Kupier Belt.
Uranus and Neptune, the Solar System’s ice giant planets. Credit: Wikipedia Commons
But first we still have two more planets to look at, Uranus and Neptune.
Uranus, and Neptune, are sometimes known as Ice Giants instead of Gas Giants because it has a lot more water. It also has more ammonia and methane and all three get called ices in this context because they make up most of the solid matter when you get this far out in the solar system.
While Jupiter is over a thousand times the mass of Earth, Uranus weighs in at about 15 times the Earth and has only about double the escape velocity of Earth itself, the least of any of the gas giants, and it’s strange rotation, and its strange tilt contributes to it having much less wind than other giants. Additionally the gravity is just a little less than Earth’s in the atmosphere so we have the option for floating habitats again, though it would be a lot more like a submarine than a hot air balloon.
Like Venus, Uranus has very long days, at least in terms of places receiving continual sunlight, the poles get 42 years of perpetual sunlight then 42 of darkness. Sunlight being a relative term, the light is quite minimal especially inside the atmosphere. The low wind in many places makes it a good spot for gas extraction, such as Helium-3, and it’s a good planet to try to scoop gas from or even have permanent installations.
Now Uranus has a large collection of moons as well, useful and colonizable like the other moons we have looked at, but otherwise unremarkable beyond being named for characters from Shakespeare, rather than the more common mythological names. None have atmospheres though there is a possibility Oberon or Titania might have subsurface oceans.
Neptune makes for a brief entry, it is very similar to Uranus except it has the characteristically high winds of gas giants that Uranus’s skewed poles mitigate, meaning it has no advantages over Uranus and the disadvantages of high wind speeds everywhere and being even further from the Sun. It too has moons and one of them, Triton, is thought to have subsurface oceans as well. Triton also presumably has a good amount of nitrogen inside it since it often erupts geysers of nitrogen from its surface.
Neptune’s largest moon Triton photographed on August 25, 1989 by Voyager 2. Credit: NASA
Triton is one of the largest moons in the solar system, coming in seventh just after our Moon, number 5, and Europa at number 6. Meaning that were it not a moon it would probably qualify as a Dwarf Planet and it is often thought Pluto might be an escaped moon Neptune. So Triton might be one that didn’t escape, or didn’t avoid getting captured. In fact there are an awful lot of bodies in this general size range and composition wandering about in the outer regions of our solar system as we get out into the Kuiper Belt.
Pluto and its cohorts in the icy-asteroid-rich Kuiper Belt beyond the orbit of Neptune. Credit: NASA
The Kuiper Belt is one of those things that has a claim on the somewhat arbitrary and hazy boundary marking the edge of the Solar System. It extends from out past Neptune to beyond Pluto and contains a good deal more mass than the asteroid Belt. It is where a lot of our comets come from and while there is plenty of rocks out there they tend to be covered in ice. In other words it is like our asteroid belt only there’s more of it and the one thing the belt is not very abundant in, water and hydrogen in general, is quite abundant out there. So if you have a power source life fusion they can be easily terraformed and are just as attractive as a source of minerals as the various asteroids and moons closer in.
Discovered in 2005, Makemake, a Kuiper Belt Object (KBO) has . Credit: NASA
We mentioned the idea of living inside hollowed out asteroids earlier and you can use the same trick for comets. Indeed you could shape them to be much bigger if you like, since they would be hollow and ice isn’t hard to move and shape especially in zero gravity. Same trick as before, you place a spinning cylinder inside it. Not all the objects entirely ice and indeed your average comet is more a frozen ball of mud then ice with rocky cores. We think a lot of near Earth Asteroids are just leftover comets. So they are probably pretty good homes if you have fusion, lots of fuel and raw materials for both life and construction.
This is probably your cheapest interstellar spacecraft too, in terms of effort anyway. People often talk about re-directing comets to Mars to bring it air and water, but you can just as easily re-direct it out of the solar system entirely. Comets tend to have highly eccentric orbits, so if you capture one when it is near the Sun you can accelerate it then, actually benefiting from the Oberth Effect, and drive it out of the solar system into deep space. If you have a fusion power source to live inside one then you also have an interstellar spaceship drive, so you just carve yourself a small colony inside the comet and head out into deep space.
You’ve got supplies that will last you many centuries at least, even if it were home to tens of thousand of people, and while we think of smaller asteroids and comets as tiny, that’s just in comparison to planets. These things tend to be the size of mountain so there is plenty of living space and a kilometer of dirty ice between you and space makes a great shield against even the kinds of radiation and collisions you can experience at relativistic speeds.
Artists’ impression of the Kuiper belt and Oort cloud. Credit: NASA/JPL
Now the Oort Cloud is much like the Kupier Belt but begins even further out and extends out probably an entire light year or more. We don’t have a firm idea of its exact dimensions or mass, but the current notion is that it has at least several Earth’s worth of mass, mostly in various icy bodies. These will be quite numerous, estimates usually assumes at least trillion icy bodies a kilometer across or bigger, and even more smaller ones. However the volume of space is so large that those kilometer wide bodies might each be a around a billion kilometers distant from neighbors, or about a light hour. So it is spread out quite thinly, and even the inner edge is about 10 light days away.
That means that from a practical standpoint there is no source of power out there, the sun is simply too diffuse for even massive collections of mirrors and solar panels to be of use. It also means light-speed messages home or to neighbors are quite delayed. So in terms of communication it is a lot more like pre-modern times in sparsely settled lands where talking with your nearest neighbors might require an hour long walk over to their farm, and any news from the big cities might take months to percolate out to you.
There’s probably uranium and thorium out there to be found, maybe a decent amount of it, so fission as a power source is not ruled out. If you have fusion instead though each of these kilometer wide icy bodies is like a giant tank of gasoline, and as with the Kupier Belt, ice makes a nice shield against impacts and radiation.
And while there might be trillions of kilometer wide chunks of ice out there, and many more smaller bodies, you would have quite a few larger ones too. There are almost certainly tons of planets in the Pluto size-range out these, and maybe even larger ones. Even after the Oort cloud you would still have a lot of these deep space rogue planets which could bridge the gap to another solar system’s Oort Cloud. So if you have fusion you have no shortage of energy, and could colonize trillions of these bodies. There probably is a decent amount of rock and metal out there too, but that could be your major import/export option shipping home ice and shipping out metals.
That’s the edge of the Solar System so that’s the end of this article. If you haven’t already read the other half, colonizing the inner Solar System, head on over now.
Chris Hadfield recently explained how humanity should create a Moon base before attempting to colonize Mars. Credit: Foster + Partners is part of a consortium set up by the European Space Agency to explore the possibilities of 3D printing to construct lunar habitations.
Credit: ESA/Foster + Partners
Ever since we began sending crewed missions to the Moon, people have been dreaming of the day when we might one day colonize it. Just imagine, a settlement on the lunar surface, where everyone constantly feels only about 15% as heavy as they do here on Earth. And in their spare time, the colonists get to do all kinds of cool research trek across the surface in lunar rovers. Gotta admit, it sounds fun!
More recently, the idea of prospecting and mining on the Moon has been proposed. This is due in part to renewed space exploration, but also the rise of private aerospace companies and the NewSpace industry. With missions to the Moon schedules for the coming years and decades, it seems logical to thinking about how we might set up mining and other industries there as well?
Proposed Methods:
Several proposals have been made to establish mining operations on the Moon; initially by space agencies like NASA, but more recently by private interests. Many of the earliest proposals took place during the 1950s, in response to the Space Race, which saw a lunar colony as a logical outcome of lunar exploration.
Building a lunar base might be easier if astronauts could harvest local materials for the construction, and life support in general. Credit: NASA/Pat Rawlings
For instance, in 1954 Arthur C. Clarke proposed a lunar base where inflatable modules were covered in lunar dust for insulation and communications were provided by a inflatable radio mast. And in 1959, John S. Rinehart – the director of the Mining Research Laboratory at the Colorado School of Mines – proposed a tubular base that would “float” across the surface.
Since that time, NASA, the US Army and Air Force, and other space agencies have issued proposals for the creation of a lunar settlement. In all cases, these plans contained allowances for resource utilization to make the base as self-sufficient as possible. However, these plans predated the Apollo program, and were largely abandoned after its conclusion. It has only been in the past few decades that detailed proposals have once again been made.
For instance, during the Bush Administration (2001-2009), NASA entrtained the possibility of creating a “lunar outpost”. Consistent with their Vision for Space Exploration (2004), the plan called for the construction of a base on the Moon between 2019 and 2024. One of the key aspects of this plan was the use of ISRU techniques to produce oxygen from the surrounding regolith.
These plans were cancelled by the Obama administration and replaced with a plan for a Mars Direct mission (known as NASA’s “Journey to Mars“). However, during a workshop in 2014, representatives from NASA met with Harvard geneticist George Church, Peter Diamandis from the X Prize Foundation and other experts to discuss low-cost options for returning to the Moon.
The workshop papers, which were published in a special issue of New Space, describe how a settlement could be built on the Moon by 2022 for just $10 billion USD. According to their papers, a low-cost base would be possible thanks to the development of the space launch business, the emergence of the NewSpace industry, 3D printing, autonomous robots, and other recently-developed technologies.
In December of 2015, an international symposium titled “Moon 2020-2030 – A New Era of Coordinated Human and Robotic Exploration” took place at the the European Space Research and Technology Center. At the time, the new Director General of the ESA (Jan Woerner) articulated the agency’s desire to create an international lunar base using robotic workers, 3D printing techniques, and in-situ resources utilization.
In 2010, NASA established the Robotic Mining Competition, an annual incentive-based competition where university students design and build robots to navigate a simulated Martian environment. One of the most-important aspects of the competition is creating robots that can rely on ISRU to turn local resources into usable materials. The applications produced are also likely to be of use during future lunar missions.
An early lunar outpost design based on a module design (1990). Credit: NASA/Cicorra Kitmacher
And the NewSpace industry has also been producing some interesting proposals of late. In 2010, a group of Silicon Valley entrepreneurs came together for create Moon Express, a private company that plans to offer commercial lunar robotic transportation and data services, as well as the a long-term goal of mining the Moon. In December of 2015, they became the first company competing for the Lunar X Prize to build and test a robotic lander – the MX-1.
In 2010, Arkyd Astronautics (renamed Planetary Resources in 2012) was launched for the purpose of developing and deploying technologies for asteroid mining. In 2013, Deep Space Industries was formed with the same purpose in mind. Though these companies are focused predominantly on asteroids, the appeal is much the same as lunar mining – which is expanding humanity’s resource base beyond Earth.
Resources:
Based on the study of lunar rocks, which were brought back by the Apollo missions, scientists have learned that the lunar surface is rich in minerals. Their overall composition depends on whether the rocks came from lunar maria (large, dark, basaltic plains formed from lunar eruptions) or the lunar highlands.
Moon rocks from the Apollo 11 mission. Credit: NASA
Rocks obtained from lunar maria showed large traces of metals, with 14.9% alumina (Al²O³), 11.8% calcium oxide (lime), 14.1% iron oxide, 9.2% magnesia (MgO), 3.9% titanium dioxide (TiO²) and 0.6% sodium oxide (Na²O). Those obtained from the lunar highlands are similar in composition, with 24.0% alumina, 15.9% lime, 5.9% iron oxide, 7.5% magnesia, and 0.6% titanium dioxide and sodium oxide.
These same studies have shown that lunar rocks contain large amounts of oxygen, predominantly in the form of oxidized minerals. Experiments have been conducted that have shown how this oxygen could be extracted to provide astronauts with breathable air, and could be used to make water and even rocket fuel.
The Moon also has concentrations of Rare Earth Metals (REM), which are attractive for two reasons. On the one hand, REMs are becoming increasingly important to the global economy, since they are used widely in electronic devices. On the other hand, 90% of current reserves of REMs are controlled by China; so having a steady access to an outside source is viewed by some as a national security matter.
Similarly, the Moon has significant amounts of water contained within its lunar regolith and in the permanently shadowed areas in its north and southern polar regions.This water would also be valuable as a source of rocket fuel, not to mention drinking water for astronauts.
Spectra gathered by the NASA Moon Mineralogy Mapper (M3) on India’s Chandrayaan-1 mission, showing the presence of water in Moon’s polar regions. Credit: ISRO/NASA/JPL-Caltech/Brown University/USGS
In addition, lunar rocks have revealed that the Moon’s interior may contain significant sources of water as well. And from samples of lunar soil, it is calculated that adsorbed water could exist at trace concentrations of 10 to 1000 parts per million. Initially, it was though that concentrations of water within the moon rocks was the result of contamination.
But since that time, multiple missions have not only found samples of water on the lunar surface, but revealed evidence of where it came from. The first was India’s Chandrayaan-1 mission, which sent an impactor to the lunar surface on Nov. 18th, 2008. During its 25-minute descent, the impact probe’s Chandra’s Altitudinal Composition Explorer (CHACE) found evidence of water in the Moon’s thin atmosphere.
In November 2009, the NASA LCROSS space probe made similar finds around the southern polar region, as an impactor it sent to the surface kicked up material shown to contain crystalline water. In 2012, surveys conducted by the Lunar Reconnaissance Orbiter (LRO) revealed that ice makes up to 22% of the material on the floor of the Shakleton crater (located in the southern polar region).
Hydrogen detected in the polar regions of the Moon point towards the presence of water. Credit: NASA
It has been theorized that all this water was delivered by a combination of mechanisms. For one, regular bombardment by water-bearing comets, asteroids and meteoroids over geological timescales could have deposited much of it. It has also been argued that it is being produced locally by the hydrogen ions of solar wind combining with oxygen-bearing minerals.
But perhaps the most valuable commodity on the surface of the Moon might be helium-3. Helium-3 is an atom emitted by the Sun in huge amounts, and is a byproduct of the fusion reactions that take place inside. Although there is little demand for helium-3 today, physicists think they’ll serve as the ideal fuel for fusion reactors.
The Sun’s solar wind carries the helium-3 away from the Sun and out into space – eventually out of the Solar System entirely. But the helium-3 particles can crash into objects that get in their way, like the Moon. Scientists haven’t been able to find any sources of helium-3 here on Earth, but it seems to be on the Moon in huge quantities.
Benefits:
From a commercial and scientific point of view, there are several reasons why Moon mining would be beneficial to humanity. For starters, it would be absolutely essential to any plans to build a settlement on the Moon, as in-situ resource utilization (ISRU) would be far more cost effective than transporting materials from Earth.
Artist concept of a base on the Moon. Credit: NASA, via Wikipedia
Also, it is predicted that the proposed space exploration efforts for the 21st century will require large amounts of materiel. That which is mined on the Moon would be launched into space at a fraction of the cost of what is mined here on Earth, due to the Moon’s much lower gravity and escape velocity.
In addition, the Moon has an abundance of raw materials that humanity relies on. Much like Earth, it is composed of silicate rocks and metals that are differentiated between a geochemically distinct layers. These consist of is iron-rich inner core, and iron-rich fluid outer core, a partially molten boundary layer, and a solid mantle and crust.
In addition, it has been recognized for some time that a lunar base – which would include resource operations – would be a boon for missions farther into the Solar System. For missions heading to Mars in the coming decades, the outer Solar System, or even Venus and Mercury, the ability to be resupplied from an lunar outpost would cut the cost of individual missions drastically.
Challenges:
Naturally, the prospect of setting up mining interests on the Moon also presents some serious challenges. For instance, any base on the Moon would need to be protected from surface temperatures, which range from very low to high – 100 K (-173.15 °C;-279.67 °F) to 390 K (116.85 °C; 242.33 °F) – at the equator and average 150 K (-123.15 °C;-189.67 °F) in the polar regions.
Schematic showing the stream of charged hydrogen ions carried from the Sun by the solar wind.Credit: University of Maryland/F. Merlin/McREL]Radiation exposure is also an issue. Due to the extremely thin atmosphere and lack of a magnetic field, the lunar surface experiences half as much radiation as an object in interplanetary space. This means that astronauts and/or lunar workers would at a high risk of exposure to cosmic rays, protons from solar wind, and the radiation caused by solar flares.
Then there’s the Moon dust, which is an extremely abrasive glassy substance that has been formed by billions of years of micrometeorite impacts on the surface. Due to the absence of weathering and erosion, Moon dust is unrounded and can play havoc with machinery, and poses a health hazard. Worst of all, its sticks to everything it touches, and was a major nuisance for the Apollo crews!
And while the lower gravity is attractive as far as launches are concerned, it is unclear what the long-term health effects of it will be on humans. As repeated research has shown, exposure to zero-gravity over month-long periods causes muscular degeneration and loss of bone density, as well as diminished organ function and a depressed immune system.
A lunar base, as imagined by NASA in the 1970s. Image Credit: NASA
And while there has been plenty of speculation about a “loophole” which does not expressly forbid private ownership, there is no legal consensus on this. As such, as lunar prospecting and mining become more of a possibility, a legal framework will have to be worked out that ensures everything is on the up and up.
Though it might be a long way off, it is not unreasonable to think that someday, we could be mining the Moon. And with its rich supplies of metals (which includes REMs) becoming part of our economy, we could be looking at a future characterized by post-scarcity!
It was with great fanfare that Elon Musk announced SpaceX’s plans to colonize Mars with the Interplanetary Transport System.
I really wish they’d stuck to their original name, the BFR, the Big Fabulous Rocket, or something like that.
The problem is that Interplanetary Transport System is way too close a name to another really cool idea, the Interplanetary Transport Network, which gives you an almost energy free way to travel across the entire Solar System. Assuming you’re not in any kind of rush.
When you imagine rockets blasting off for distant destinations, you probably envision pointing your rocket at your destination, firing the thrusters until you get there. Maybe turning around and slowing down again to land on the alien world. It’s how you might drive your car, or fly a plane to get from here to there.
But if you’ve played any Kerbal Space Program, you know that’s not how it works in space. Instead, it’s all about orbits and velocity. In order to get off planet Earth, you have be travelling about 8 km/s or 28,000 km/h sideways.
Artist’s concept of a Bimodal Nuclear Thermal Rocket in Low Earth Orbit. Credit: NASA
So now, you’re orbiting the Earth, which is orbiting the Sun. If you want to get to Mars, you have raise your orbit so that it matches Mars. The absolute minimum energy needed to make that transfer is known as the Hohmann transfer orbit. To get to Mars, you need to fire your thrusters until you’re going about 11.3 km/s.
Then you escape the pull of Earth, follow a nice curved trajectory, and intercept the trajectory of Mars. Assuming you timed everything right, that means you intercept Mars and go into orbit, or land on its surface, or discover a portal to hell dug into a research station on Phobos.
If you want to expend more energy, go ahead, you’ll get there faster.
But it turns out there’s another way you can travel from planet to planet in the Solar System, using a fraction of the energy you would use with the traditional Hohmann transfer, and that’s using Lagrange points.
We did a whole article on Lagrange points, but here’s a quick refresher. The Lagrange points are places in the Solar System where the gravity between two objects balances out in five places. There are five Lagrange points relating to the Earth and the Sun, and there are five Lagrange points relating to the Earth and the Moon. And there are points between the Sun and Jupiter, etc.
Illustration of the Sun-Earth Lagrange Points. Credit: NASA
Three of these points are unstable. Imagine a boulder at the top of a mountain. It doesn’t take much energy to keep it in place, but it’s easy to knock it out of balance so it comes rolling down.
Now, imagine the whole Solar System with all these Lagrange points for all the objects gravitationally interacting with each other. As planets go around the Sun, these Lagrange points get close to each other and even overlap.
And if you time things right, you can ride along in one gravitationally balanced point, and the roll down the gravity hill into the grasp of a different planet. Hang out there for a little bit and then jump orbits to another planet.
In fact, you can use this technique to traverse the entire Solar System, from Mercury to Pluto and beyond, relying only on the interacting gravity of all these worlds to provide you with the velocity you need to make the journey.
Welcome to the Interplanetary Transport Network, or Interplanetary Superhighway.
Unlike a normal highway, though, the actual shape and direction these pathways take changes all the time, depending on the current configuration of the Solar System.
A stylized example of one of the many, ever-changing routes along the ITN. Credit: NASA
If you think this sounds like science fiction, you’ll be glad to hear that space agencies have already used a version of this network to get some serious science done.
NASA greatly extended the mission of the International Sun/Earth Explorer 3, using these low energy transfers, it was able to perform its primary mission and then investigate a couple of comets.
The Japanese Hiten spacecraft was supposed to travel to the Moon, but its rocket failed to get enough velocity to put it into the right orbit. Researchers at NASA’s Jet Propulsion Laboratory calculated a trajectory that used the Lagrange points to help it move slowly and get to the Moon any way.
NASA’s Genesis Mission used the technique to capture particles from the solar wind and bring them back to the Earth.
There have been other missions to use the technique, and missions have been proposed that might exploit this technique to fully explore all the moons of Jupiter or Saturn, for example. Traveling from moon to moon when the gravity points line up.
It all sounds too good to be true, so here’s the downside. It’s slow. Really, painfully slow.
Like it can take years and even decades to move from world to world.
Imagine in the far future, there are space stations positioned at the major Lagrange points around the planets in the Solar System. Maybe they’re giant rotating space stations, like in 2001, or maybe they’re hollowed out asteroids or comets which have been maneuvered into place.
Exterior view of a Stanford torus. Bottom center is the non-rotating primary solar mirror, which reflects sunlight onto the angled ring of secondary mirrors around the hub. Painting by Donald E. Davis
They hang out at the Lagrange points using minimal fuel for station keeping. If you want to travel from one planet to another, you dock your spacecraft at the space station, refuel, and then wait for one of these low-energy trajectories to open up.
Then you just kick away from the Lagrange point, fall into the gravity well of your destination, and you’re on your way.
In the far future, we could have space stations at all the Lagrange points, and slow ferries that move from world to world along low energy trajectories, bringing cargo from world to world. Or taking passengers who can’t afford the high velocity Hohmann transfer technique.
You could imagine the space stations equipped with powerful lasers that fill your ship’s solar sails with the photons it needs to take you to the next destination. But then, I’m a sailor, so maybe I’m overly romanticizing it.
Here’s another, even more mind-bending concept. Astronomers have observed these networks open up between interacting galaxies. Want to transfer from the Milky Way to Andromeda? Just get your spacecraft to the galactic Lagrange point in a few billion years as they pass through each other. With very little energy, you’ll be able to join the cool kids in Andromeda.
I love this idea that colonizing and traveling across the Solar System doesn’t actually need to take enormous amounts of energy. If you’re patient, you can just ride the gravitational currents from world to world. This might be one of the greatest gifts the Solar System has made available to us.
Scientists, futurists, and science fiction writers have been talking about it for over a century, and fans of science fiction and futurists have fantasized about it for just as long. The portable directed-energy weapon that zaps your enemies, rendering them incapacitated or reducing them to a pile of ashes!
The concept has gone through many iterations over the decades, ranging from laser pistols and cannons to phasers. And yet, this staple of science fiction is largely based in science fact. Since the early 20th century, scientists have sought to develop a working directed-energy weapon, based on ideas put forward by many inventors and scientists.
Definition:
A”death ray” is a theoretical particle beam or electromagnetic weapon that was originally proposed independently during the 1920s and 30s by multiple scientists. From these initial proposals, research into energy-based weapons has been ongoing. While most examples come predominantly from science fiction, several applications and proposals have been produced during the latter half of the 20th century.
Directed-energy weapons, like the Death Star’s superlaser, are a common feature in science fiction. Credit: Wookieepedia / Lucasfilm
History:
During the early 20th century, many scientists claimed that they had created a working death ray. For instance, in September of 1924, British inventor Harry Grindell-Matthews attempted to sell what he reported to be a death ray that could destroy human life and bring down planes at a distance to the British Air Ministry.
While he was never able to produce a functioning model or demonstrate it to the military, news of this prompted American inventor Edwin R. Scott to claim that he was the first to develop a death ray. According to Scott, he had done so in 1923, which was the result of the nine years he spent as a student and protege of Charles P. Steinmetz – a German-American professor at Union College, New York.
In 1934, Spanish inventor Antonion Longoria claimed to have invented a death ray machine which he had tested on pigeons at a distance of about 6.5 km (4 miles). He also claimed to have killed mice that were enclosed in a thick-walled metal chamber.
However, it was famed inventor and electrical engineer Nikola Tesla who provided the most detailed framework for such a device. In a 1934 interview with Time Magazine, Tesla explained the concept of a “teleforce” (or directed energy) weapon which would be capable of destroying entire squadrons of airplanes or an entire army at a distance of 400 km (250 miles).
Photograph of Tesla sitting in his Colorado Springs laboratory with his “magnifying transmitter” generating millions of volts. Credit: Wikipedia Commons/Century Magazine/Dickenson V. AlleyTesla tried to interest the US War Department and several European countries in the device at the time, though none contracted with Tesla to build it. As Tesla described his invention in an article titled “A Machine to End War“, which appeared in Liberty Magazine in 1935:
“this invention of mine does not contemplate the use of any so-called ‘death rays’. Rays are not applicable because they cannot be produced in requisite quantities and diminish rapidly in intensity with distance. All the energy of New York City (approximately two million horsepower) transformed into rays and projected twenty miles, could not kill a human being, because, according to a well known law of physics, it would disperse to such an extent as to be ineffectual. My apparatus projects particles which may be relatively large or of microscopic dimensions, enabling us to convey to a small area at a great distance trillions of times more energy than is possible with rays of any kind. Many thousands of horsepower can thus be transmitted by a stream thinner than a hair, so that nothing can resist.”
Based on his descriptions, the device would constitute a large tower that could be mounted on top of a building, positioned either next to shores or near crucial infrastructure. This weapon, he claimed, would be defensive in nature, in that it would make any nation employing it impregnable to attack from air, land or sea, and up to a distance of 322 km (200 miles).
During World War II, multiple efforts were mounted by the Axis powers to create so-called “death rays”. For instance, Imperial Japan developed a concept they called “Ku-Go”, which sought to use microwaves created in a large magnetron as a weapon.
Dresden, 1945, view from the city hall (Rathaus) over the destroyed city. Credit: Wikipedia Commons/ Deutsche Fotothek?
Meanwhile, the Nazis mounted two projects, one which was led by the researcher known as Schiebold that involved a particle accelerator and beryllium rods. The second, led by Dr. Rolf Wideroe, was developed at the Dresden Plasma Physics Laboratory until it was bombed in Feb. 1945. In April of that year, as the war was coming to close, the device was taken into custody by the US Army.
On January 7th, 1943, engineer and inventor Nikola Tesla died in his room at the Hotel New Yorker in Manhattan. A story quickly developed that within his room, Tesla had scientific paper in his possession that provided the most detailed description yet for a death ray. These documents, it was claimed, had been seized by the US military, who wanted them for the sake of the war effort.
Examples in Science Fiction:
Ray guns, and other examples of directed-energy weapons have been a common feature in science fiction for over a century. One of the first known examples comes from H.G. Wells seminal book, War of the Worlds, which featured Martian war machines that used “heat rays”. However, the first use of the term was in The Messiah of the Cylinder (1917), by Victor Rousseau Emanuel.
Ray guns were also a regular feature in comic books like Buck Rogers (first published in 1928) and Flash Gordon, published in 1934. In Alfred Noyes’ 1940 novel The Last Man (released as No Other Man in the US), a death ray developed by a German scientist named Mardok is unleashed in a global war and almost wipes out the human race.
H.G. Wells’ 1898 novel about a Martian invasion, War of the Worlds, featured alien machines using heat rays to spread havoc. Credit: Henrique Alvim Correa (1906)
The concept of the blaster was introduced by Isaac Asimov’s The Foundation Series, which were described as nuclear-powered handheld weapons that fired energetic particles. In Frank Herbert’s Dune series, energy weapons take the form of continuous-wave laser projectors (lasguns), which are rendered obsolete by the invention of “Holtzman shields”.
According to Herbert, the interaction of a lasgun blast and this force field results in a nuclear explosion which typically kills both the gunner and the target. Further examples of death rays can be found in just about any science fiction franchise, ranging from phasers (Star Trek) and laser blasters (Star Wars) to spaceship-mounted beam cannons.
Modern Development:
In terms of real-world applications, many attempts have been made to create directed-energy weapons for offensive and defensive purposes. For instance, the development of radar before World War II was the result of attempts to find applications for directed electromagnetic energy (in this case, radio waves).
In the 1980s, U.S. President Ronald Reagan proposed the Strategic Defense Initiative (SDI) program (nicknamed “Star Wars”). It suggested that lasers, perhaps space-based X-ray lasers, could destroy ICBMs in flight. During the Iraq War, electromagnetic weapons, including high power microwaves were used by the U.S. military to disrupt and destroy the Iraqi electronic systems.
An artist’s concept of a Space Laser Satellite Defense System. Credit: USAF
On March 18th, 2009 Northrop Grumman announced that its engineers in Redondo Beach had successfully built and tested an electric laser capable of producing a 100-kilowatt ray of light, powerful enough to destroy cruise missiles, artillery, rockets and mortar rounds. And on July 19th, 2010, an anti-aircraft laser was unveiled at the Farnborough Airshow, described as the “Laser Close-In Weapon System”.
In 2014, the US Navy made headlines when they unveiled their AN/SEQ-3 Laser Weapon System (or XN-1 LaWS), a directed-energy weapon designed for use on military vessels. Ostensibly, the purpose of the weapon is defensive, designed to either blind enemy sensors (when set to low-intensity) or shoot down unmanned aerial vehicles (UAVs) when set to high-intensity.
Then is what is known as “Active Denial Systems”, which use a microwave source to heat up the water in the target’s skin, thus causing physical pain. Currently, this concept is being developed by the US Air Force Research Laboratory and Raytheon – a US defense contractor – as a means of riot-control.
A Dazzler is another type of directed-energy weapon, one which uses infrared or visible light to temporarily blind an enemy. Targets can include human beings, or their sensors (particularly in the infrared band). The emitters are usually lasers (hence the term “laser dazzler”)and can be portable or mounted on the outside of vehicles (as with the Russian T-80 and T-90 tank).
The personnel halting and stimulation response rifle (PHASR) is a prototype non-lethal laser dazzler developed by the Air Force Research Laboratory’s Directed Energy Directorate, U.S. Department of Defense. Credit: USAF
An example of the former is the Personnel Halting And Stimulation Response rifle (PHASR), a prototype non-lethal laser dazzler being developed by the US Air Force Research Laboratory’s Directed Energy Directorate. Its purpose is give infantry or other military personnel the ability to temporarily disorient and blind a target without causing permanent damage.
Blinding laser weapons were banned by treated under the UN Protocol on Blinding Laser Weapons, which was passed in 1995. However, the terms of this protocol do not apply to directed-energy weapons that inflict only temporary blindness.
We’ve come a long way since the term “raygun” became a household name. At this rate, who knows what the future will hold? Will Tesla’s dream of a Death Ray ever come true? Will we see directed-energy satellites put in orbit, or handheld lasers becoming the mainstay of armed forces and space explorers? Hard to say. All we can be sure of is that the truth will likely be stranger than the fiction!
An artist's impression of the accretion disc around the supermassive black hole that powers an active galaxy. Astronomers want to know if the energy radiated from a black hole is caused by jets of material shooting away from the hole, or by the accretion disk of swirling material near the hole. Credit: NASA/Dana Berry, SkyWorks Digital
In the 1970s, astronomers became aware of a compact radio source at the center of the Milky Way Galaxy – which they named Sagittarius A. After many decades of observation and mounting evidence, it was theorized that the source of these radio emissions was in fact a supermassive black hole (SMBH). Since that time, astronomers have come to theorize that SMBHs at the heart of every large galaxy in the Universe.
Most of the time, these black holes are quiet and invisible, thus being impossible to observe directly. But during the times when material is falling into their massive maws, they blaze with radiation, putting out more light than the rest of the galaxy combined. These bright centers are what is known as Active Galactic Nuclei, and are the strongest proof for the existence of SMBHs.
Description:
It should be noted that the enormous bursts in luminosity observed from Active Galactic Nuclei (AGNs) are not coming from the supermassive black holes themselves. For some time, scientists have understood that nothing, not even light, can escape the Event Horizon of a black hole.
Instead, the massive burst of radiations – which includes emissions in the radio, microwave, infrared, optical, ultra-violet (UV), X-ray and gamma ray wavebands – are coming from cold matter (gas and dust) that surround the black holes. These form accretion disks that orbit the supermassive black holes, and gradually feeding them matter.
The incredible force of gravity in this region compresses the disk’s material until it reaches millions of degrees kelvin. This generates bright radiation, producing electromagnetic energy that peaks in the optical-UV waveband. A corona of hot material forms above the accretion disc as well, and can scatter photons up to X-ray energies.
A large fraction of the AGN’s radiation may be obscured by interstellar gas and dust close to the accretion disc, but this will likely be re-radiated at the infrared waveband. As such, most (if not all) of the electromagnetic spectrum is produced through the interaction of cold matter with SMBHs.
The interaction between the supermassive black hole’s rotating magnetic field and the accretion disk also creates powerful magnetic jets that fire material above and below the black hole at relativistic speeds (i.e. a significant fraction of the speed of light). These jets can extend for hundreds of thousands of light-years, and are a second potential source of observed radiation.
Types of AGN:
Typically, scientists divide AGN into two categories, which are referred to as “radio-quiet” and “radio-loud” nuclei. The radio-loud category corresponds to AGNs that have radio emissions produced by both the accretion disk and the jets. Radio-quiet AGNs are simpler, in that any jet or jet-related emission are negligible.
Carl Seyfert discovered the first class of AGN in 1943, which is why they now bear his name. “Seyfert galaxies” are a type of radio-quiet AGN that are known for their emission lines, and are subdivided into two categories based on them. Type 1 Seyfert galaxies have both narrow and broadened optical emissions lines, which imply the existence of clouds of high density gas, as well as gas velocities of between 1000 – 5000 km/s near the nucleus.
Type 2 Seyferts, in contrast, have narrow emissions lines only. These narrow lines are caused by low density gas clouds that are at greater distances from the nucleus, and gas velocities of about 500 to 1000 km/s. As well as Seyferts, other sub classes of radio-quiet galaxies include radio-quiet quasars and LINERs.
Low Ionisation Nuclear Emission-line Region galaxies (LINERs) are very similar to Seyfert 2 galaxies, except for their low ionization lines (as the name suggests), which are quite strong. They are the lowest-luminosity AGN in existence, and it is often wondered if they are in fact powered by accretion on to a supermassive black hole.
Artist’s representation of an active galactic nucleus (AGN) at the center of a galaxy. Credit: NASA/CXC/M.Weiss
Radio-loud galaxies can also be subdivded into categories like radio galaxies, quasars, and blazars. As the name suggests, radio galaxies are elliptical galaxies that are strong emitters of radiowaves. Quasars are the most luminous type of AGN, which have spectra similar to Seyferts.
However, they are different in that their stellar absorption features are weak or absent (meaning they are likely less dense in terms of gas) and the narrow emission lines are weaker than the broad lines seen in Seyferts. Blazars are a highly variable class of AGN that are radio sources, but do not display emission lines in their spectra.
Detection:
Historically speaking, a number of features have been observed within the centers of galaxies that have allowed for them to be identified as AGNs. For instance, whenever the accretion disk can be seen directly, nuclear-optical emissions can be seen. Whenever the accretion disk is obscured by gas and dust close to the nucleus, an AGN can be detected by its infra-red emissions.
Then there are the broad and narrow optical emission lines that are associated with different types of AGN. In the former case, they are produced whenever cold material is close to the black hole, and are the result of the emitting material revolving around the black hole with high speeds (causing a range of Doppler shifts of the emitted photons). In the former case, more distant cold material is the culprit, resulting in narrower emission lines.
Image taken by the Hubble Space Telescope of a 5000-light-year-long jet ejected from the active galaxy M87. Credit: NASA/The Hubble Heritage Team (STScI/AURA)
Next up, there are radio continuum and x-ray continuum emissions. Whereas radio emissions are always the result of the jet, x-ray emissions can arise from either the jet or the hot corona, where electromagnetic radiation is scattered. Last, there are x-ray line emissions, which occur when x-ray emissions illuminate the cold heavy material that lies between it and the nucleus.
These signs, alone or in combination, have led astronomers to make numerous detections at the center of galaxies, as well as to discern the different types of active nuclei out there.
The Milky Way Galaxy:
In the case of the Milky Way, ongoing observation has revealed that the amount of material accreted onto Sagitarrius A is consistent with an inactive galactic nucleus. It has been theorized that it had an active nucleus in the past, but has since transitioned into a radio-quiet phase. However, it has also been theorized that it might become active again in a few million (or billion) years.
When the Andromeda Galaxy merges with our own in a few billion years, the supermassive black hole that is at its center will merge with our own, producing a much more massive and powerful one. At this point, the nucleus of the resulting galaxy – the Milkdromeda (Andrilky) Galaxy, perhaps? – will certainly have enough material for it to be active.
The discovery of active galactic nuclei has allowed astronomers to group together several different classes of galaxies. It’s also allowed astronomers to understand how a galaxy’s size can be discerned by the behavior at its core. And last, it has also helped astronomers to understand which galaxies have undergone mergers in the past, and what could be coming for our own someday.
The night sky above the Danish 1.54-metre telescope at ESO's La Silla Observatory. The Magellanic Clouds are visible to the right of the central bar of the Milky Way. Credit: ESO/Z. Bardon
Since ancient times, human beings have been staring at the night sky and been amazed by the celestial objects looking back at them. Whereas these objects were once thought to be divine in nature, and later mistaken for comets or other astrological phenomena, ongoing observation and improvements in instrumentation have led to these objects being identified for what they are.
For example, there are the Small and Large Magellanic Clouds, two large clouds of stars and gas that can be seen with the naked eye in the southern hemisphere. Located at a distance of 200,000 and 160,000 light years from the Milky Way Galaxy (respectively), the true nature of these objects has only been understand for about a century. And yet, these objects still have some mysteries that have yet to be solved.
Characteristics:
The Large Magellanic Cloud (LMC) and the neighboring the Small Magellanic Cloud (SMC) are starry regions that orbit our galaxy, and look conspicuously like detached pieces of the Milky Way. Though they are separated by 21 degrees in the night sky – about 42 times the width of the full moon – their true distance is about 75,000 light-years from each other.
Ultraviolet view of the Large Magellanic Cloud from Swift’s Ultraviolet/Optical Telescope. Credit: NASA/Swift/S. Immler (Goddard) and M. Siegel (Penn State)
The Large Magellanic Cloud is located about 160,000 light-years from the Milky Way, in the constellation Dorado. This makes it the 3rd closest galaxy to us, behind the Sagittarius Dwarf and Canis Major Dwarf galaxies. Meanwhile, the Small Magellanic Cloud is located in the constellation of Tucana, about 200,000 light-years away.
The LMC is roughly twice the diameter of the SMC, measuring some 14,000 light-years across vs. 7,000 light years (compared to 100,000 light years for the Milky Way). This makes it the 4th largest galaxy in our Local Group of galaxies, after the Milky Way, Andromeda and the Triangulum Galaxy. The LMC is about 10 billion times as massive as our Sun (about a tenth the mass of the Milky Way), while the SMC is equivalent to about 7 billion Solar Masses.
In terms of structure, astronomers have classified the LMC as an irregular type galaxy, but it does have a very prominent bar in its center. Ergo, it’s possible that it was a barred spiral before its gravitational interactions with the Milky Way. The SMC also contains a central bar structure and it is speculated that it too was once a barred spiral galaxy that was disrupted by the Milky Way to become somewhat irregular.
Aside from their different structure and lower mass, they differ from our galaxy in two major ways. First, they are gas-rich – meaning that a higher fraction of their mass is hydrogen and helium – and they have poor metallicity, (meaning their stars are less metal-rich than the Milky Way’s). Both possess nebulae and young stellar populations, but are made up of stars that range from very young to the very old.
The Small Magellanic Cloud as seen by Swift’s Ultraviolet/Optical Telescope. This composite of 656 separate pictures has a cumulative exposure time of 1.8 days. Credit: NASA/Swift/S. Immler (Goddard) and M. Siegel (Penn State)
In fact, this abundance in gas is what ensures that the Magellanic Clouds are able to create new stars, with some being only a few hundred million years in age. This is especially true of the LMC, which produces new stars in large quantities. A good example of this is it’s glowing-red Tarantula Nebula, a gigantic star-forming region that lies 160,000 light-years from Earth.
Astronomers estimate that the Magellanic Clouds were formed approximately 13 billion years ago, around the same time as the Milky Way Galaxy. It has also been believed for some time that the Magellanic Clouds have been orbiting the Milky Way at close to their current distances. However, observational and theoretical evidence suggests that the clouds have been greatly distorted by tidal interactions with the Milky Way as they travel close to it.
This indicates that they are not likely to have frequently got as close to the Milky Way as they are now. For instance, measurements conducted with the Hubble Space Telescope in 2006 suggested that the Magellanic Clouds may be moving too fast to be long terms companions of the Milky Way. In fact, their eccentric orbits around the Milky Way would seem to indicate that they came close to our galaxy only once since the universe began.
The Small and Large Magellanic Clouds visible over the Paranal Observatory in Chile. Credit: ESO/J. Colosimo
This was followed in 2010 by a study that indicated that the Magellanic Clouds may be passing clouds that were likely expelled from the Andromeda Galaxy in the past. The interactions between the Magellanic Clouds and the Milky Way is evidenced by their structure and the streams of neutral hydrogen that connects them. Their gravity has affected the Milky Way as well, distorting the outer parts of the galactic disk.
History of Observation:
In the southern hemisphere, the Magellanic clouds were a part of the lore and mythology of the native inhabitants, including the Australian Aborigines, the Maori of New Zealand, and the Polynesian people of the South Pacific. For the latter, they served as important navigational markers, while the Maori used them as predictors of the winds.
While the study Magellanic Clouds dates back to the 1st millennium BCE, the earliest surviving record comes from the 10th century Persian astronomer Al Sufi. In his 964 treatise, Book of Fixed Stars, he called the LMC al-Bakr (“the Sheep”) “of the southern Arabs”. He also noted that the Cloud is not visible from northern Arabia or Baghdad, but could be seen at the southernmost tip of Arabian Peninsula.
By the late 15th century, Europeans are believed to have become acquainted with the Magellanic Clouds thanks to exploration and trade missions that took them south of the equator. For instance, Portuguese and Dutch sailors came to know them as the Cape Clouds, since they could only be viewed when sailing around Cape Horn (South America) and the Cape of Good Hope (South Africa).
Panoramic view of the Large and Small Magellanic Clouds above the ESO’s VLT observation site in Chile. Credit: ESO/Y. Beletsky
During the circumnavigation of the Earth by Ferdinand Magellan (1519–22), the Magellanic Clouds were described by Venetian Antonio Pigafetta (Magellan’s chronicler) as dim clusters of stars. In 1603, German celestial cartographer Johann Bayer published his celestial atlas Uranometria, where he named the smaller cloud “Nebecula Minor” (Latin for “Little Cloud”).
Between 1834 and 1838, English astronomer John Herschel conducted surveys of the southern skies from the Royal Observatory at the Cape of Good Hope. While observing the SMC, he described it as a cloudy mass of light with an oval shape and a bright center, and catalogued a concentration of 37 nebulae and clusters within it.
In 1891, the Harvard College Observatory opened an observing station in southern Peru. From 1893-1906, astronomers used the observatory’s 61 cm (24 inch) telescope to survey and photograph the LMC and SMC. One such astronomers was Henriette Swan Leavitt, who used the observatory to discover Cephied Variable stars in the SMC.
Her findings were published in 1908 a study titled “1777 variables in the Magellanic Clouds“, in which she showed the relationship between these star’s variability period and luminosity – which became a very reliable means of determining distance. This allowed the SMCs distance to be determined, and became the standard method of measuring the distance to other galaxies in the coming decades.
Hubble image of variable star RS Puppis, a Cepheid Variable located in the Milky Way Galaxy. Credit: NASA/ESA/Hubble Heritage Team
As noted already, in 2006, measurements made suing the Hubble Space Telescope were announced that suggested the Large and Small Magellanic Clouds may be moving too fast to be orbiting the Milky Way. This has given rise to the theory that they originated in another galaxy, most likely Andromeda, and were kicked out during a galactic merger.
Given their composition, these clouds – especially the LMC – will continue making new stars for some time to come. And eventually, millions of years from now, these clouds may merge with our own Milky Way Galaxy. Or, they could keep orbiting us, passing close enough to suck up hydrogen and keep their star-forming process going.
But in a few billion years, when the Andromeda Galaxy collides with our own, they may find themselves having no choice but to merge with the giant galaxy that results. One might say Andromeda regrets spitting them out, and is coming to collect them!
Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at Messier 26 open star cluster. Enjoy!
Back in the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of these objects so that others wouldn’t make the same mistake. Consisting of 100 objects, the Messier Catalog would come to be viewed by posterity as a major milestone in the study of Deep Space Objects.
One of these objects is Messier 26, an open star cluster located about 5,000 light years from the Earth in the direction of the Scutum Constellation. While somewhat faint compared to other objects that share its section of the sky, this star field remains a source of mystery to astronomers, thanks to what appears to be a low-density star field at its nucleus.
Description:
When this cloud of stars formed some 89 million years ago, it was probably far more compact than today’s size of a 22 light year span. At a happy distance of about 5,000 light years from our solar system, we can’t quite see into the nucleus to determine just how dense it may actually be because of an obscuring cloud of interstellar matter.
Image of the Messier 26 Open Star Cluster. Credit: Wikisky
However, we do know a little bit about the stars contained within it. As astronomer James Cuffey suggested in a paper titled “The Galactic Clusters NGC 6649 and NGC 6694“, which appeared in July 1940 issue of The Astrophysical Journal:
“The relations between color and apparent magnitude show that NGC 6694 contains a well-defined main sequence and a slight indication of a giant branch. A zone of low star density 3′ from the center of NGC 6694 is noted. The ratio between general and selective absorption is estimated from the available data on red color indices in obscured clusters. Although uncertain in many cases, the results tend to confirm the ratio predicted by the law of scattering.”
However boring a field of stars may look upon first encounter, studies are important to our understanding how our galaxy evolved and the timeline incurred. As Kayla Young of the Manhasset Science Research team said:
“Star Clusters are unique because all of the stars in the cluster essentially have the same age and are roughly the same distance from Earth. Therefore, the purpose was to determine if a correlation exists between mean absolute magnitude and age of a star cluster. The absolute magnitude for star cluster NGC 6694 was calculated to be about 1.34 + .9. Using the B-V (Photometric Analysis) data ages were also calculated. After a scatter plot was created, the line of best fit demonstrated an exponential relation between the age and absolute magnitude.”
The M26 Open Star Cluster. Credit: NOAO/AURA/NSF
History of Observation:
Messier 26 was first observed by Charles Messier himself on June 20th, 1764. As he wrote of the discovery at the time:
“I discovered another cluster of stars near Eta and Omicron in Antinous [now Alpha and Delta Scuti] among which there is one which is brighter than the others: with a refractor of three feet, it is not possible to distinguish them, it requires to employ a strong instrument: I saw them very well with a Gregorian telescope which magnified 104 times: among them one doesn’t see any nebulosity, but with a refractor of 3 feet and a half, these stars don’t appear individually, but in the form of a nebula; the diameter of that cluster may be 2 minutes of arc. I have determined its position with regard to the star o of Antinous, its right ascension is 278d 5′ 25″, and its declination 9d 38′ 14″ south.”
Later, Bode would report a few stars with nebulosity – a field that simply wouldn’t resolve to his telescope. William Herschel would spare it but only a brief glance, saying: “A cluster of scattered stars, not rich.” While John Herschel would later go on to class it with its NGC designation, it was Admiral Smyth who would most aptly describe M26 for the true galactic cluster we know it to be. As he wrote upon viewing it in April of 1835:
“A small and coarse, but bright, cluster of stars, preceding the left foot of Antinous, in a fine condensed part of the Milky Way; and it follows 2 Aquilae by only a half degree. The principle members of this group lie nearly in a vertical position with the equatorial line, and the place is that of a small pair in the south, or upper portion of the field [in telescope]. This neat double star is of the 9th and 10th magnitudes, with an angle [PA] = 48 deg, and is followed by an 8th [mag star], the largest [brightest] in the assemblage, by 4s. Altogether the object is pretty, and must, from all analogy, possess affinity among its various components; but the collocation and adjustment of these wondrous firmamental clusters, and their probable distances, almost stun our present faculties. There are many astral splashes in this crowded district of the Galaxy, among which fine specimens of what may be termed luminiferous ether, are met with.”
The location of Messier 26 within the Scutum Constellation. Credit: IAU/Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)
Locating Messier 26:
Finding Messier 26 in binoculars is easy as far as location goes – but not so easy distinguishing it from the starfield. Begin with the constellation of Aquila and its brightest star – Alpha. As you move southwest, count the stars down the Eagle’s back. When you reach three you are at the boundary of the constellation of Scutum. While maps make Scutum’s stars appear easy to find, they really aren’t.
The next most easily distinguished star in the line in Alpha Scutii. Aim your binoculars or finderscope there and you’ll see northern Epsilon and southern Delta to the east. Messier 26 is slightly southeast of Delta and will appear as a slight compression in the starfield, and you will be able to resolve a few individual stars to larger ones. Using a finderscope, it will appear as a very vague brightening – perhaps not seen at all depending on your finder’s aperture.
In even a small telescope, however, you’ll be pleased with what you see! Medium magnification will light up this 8th magnitude galactic star cluster and mid-sized instruments will fully resolve it. Power up! See how many stars you can – and can’t – resolve in this dusty, curtained, distant beauty!
And here are the quick facts to help you on your way!
Object Name: Messier 26 Alternative Designations: M26, NGC 6694 Object Type: Open Galactic Star Cluster Constellation: Scutum Right Ascension: 18 : 45.2 (h:m) Declination: -09 : 24 (deg:m) Distance: 5.0 (kly) Visual Brightness: 8.0 (mag) Apparent Dimension: 15.0 (arc min)
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