Back in 1993, Carl Sagan encountered a puzzle. The Galileo spacecraft spotted flashes coming from Earth, and nobody could figure out what they were. They called them ‘specular reflections’ and they appeared over ocean areas but not over land.
The images were taken by the Galileo space probe during one of its gravitational-assist flybys of Earth. Galileo was on its way to Jupiter, and its cameras were turned back to look at Earth from a distance of about 2 million km. This was all part of an experiment aimed at finding life on other worlds. What would a living world look like from a distance? Why not use Earth as an example?
Fast-forward to 2015, when the National Oceanographic and Atmospheric Administration (NOAA) launched the Deep Space Climate Observatory (DSCOVER) spacecraft. DSCOVER’s job is to orbit Earth a million miles away and to warn us of dangerous space weather. NASA has a powerful instrument on DSCOVER called the Earth Polychromatic Imaging Camera (EPIC.)
Every hour, EPIC takes images of the sunlit side of Earth, and these images can be viewed on the EPIC website. (Check it out, it’s super cool.) People began to notice the same flashes Sagan saw, hundreds of them in one year. Scientists in charge of EPIC started noticing them, too.
One of the scientists is Alexander Marshak, DSCOVR deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. At first, he noticed them only over ocean areas, the same as Sagan did 25 years ago. Only after Marshak began investigating them did he realize that Sagan had seen them too.
Back in 1993, Sagan and his colleagues wrote a paper discussing the results from Galileo’s examination of Earth. This is what they said about the reflections they noticed: “Large expanses of blue ocean and apparent coastlines are present, and close examination of the images shows a region of [mirror-like] reflection in ocean but not on land.”
Marshak surmised that there could be a simple explanation for the flashes. Sunlight hits a smooth part of an ocean or lake, and reflects directly back to the sensor, like taking a flash-picture in a mirror. Was it really that much of a mystery?
When Marshak and his colleagues took another look at the Galileo images showing the flashes, they found something that Sagan missed back in 1993: The flashes appeared over land masses as well. And when they looked at the EPIC images, they found flashes over land masses. So a simple explanation like light reflecting off the oceans was no longer in play.
“We found quite a few very bright flashes over land as well.” – Alexander Marshak, DSCOVR Deputy Project Scientist
“We found quite a few very bright flashes over land as well,” he said. “When I first saw it I thought maybe there was some water there, or a lake the sun reflects off of. But the glint is pretty big, so it wasn’t that.”
But something was causing the flashes, something reflective. Marshak and his colleagues, Tamas Varnai of the University of Maryland, Baltimore County, and Alexander Kostinski of Michigan Technological University, thought of other ways that water could cause the flashes.
The primary candidate was ice particles high in Earth’s atmosphere. High-altitude cirrus clouds contain tiny ice platelets that are horizontally aligned almost perfectly. The trio of scientists did some experiments to find the cause of the flashes, and published their results in a new paper published in Geophysical Research Letters.
“Lightning doesn’t care about the sun and EPIC’s location.” – Alexander Marshak, DSCOVR Deputy Project Scientist
As their study details, they first catalogued all of the reflective glints that EPIC found over land; 866 of them in a 14 month period from June 2015 to August 2016. If these flashes were caused by reflection, then they would only appear on locations on the globe where the angle between the Sun and Earth matched the angle between the DSCOVER spacecraft and Earth. As the catalogued the 866 glints, they found that the angle did match.
This ruled out something like lightning as the cause of the flashes. But as they continued their work plotting the angles, they came to another conclusion: the flashes were sunlight reflecting off of horizontal ice crystals in the atmosphere. Other instruments on DSCOVR confirmed that the reflections were coming from high in the atmosphere, rather than from somewhere on the surface.
“The source of the flashes is definitely not on the ground. It’s definitely ice, and most likely solar reflection off of horizontally oriented particles.” -Alexander Marshak, DSCOVR Deputy Project Scientist
Mystery solved. But as is often the case with science, answering one question leads to a couple other questions. Could detecting these glints be used in the study of exoplanets somehow? But that’s one for the space science community to answer.
As for Marshak, he’s an Earth scientist. He’s investigating how common these horizontal ice particles are, and what effect they have on sunlight. If that impact is measurable, then it could be included in climate modelling to try to understand how Earth retains and sheds heat.
Many people love to ask, why does it always rain on me? There are those who would like to know why it rains so much when they are sad, when they feel like going out, or only when they decide to jog or take their pet for a walk. There are no easy answers for these arguably subjective questions. However, if one to ask “why does it rain”, the answer would be much simpler.
For starters, rain is liquid precipitation, as opposed to non-liquid kinds (such as snow, hail and sleet). It begins with the vaporization of water near the Earth’s surface, in the form of rivers, lakes, oceans or ground water, provided there are atmospheric temperatures above melting point of water (0°C). This is followed by the condensation of atmospheric water vapor into drops of water that are heavy enough to fall, often making it to the surface.
Precipitation is also a major component of the hydrological cycle – aka. “water cycle“. This is the term used to describe the continuous movement of water on, above, and below the Earth, and is responsible for depositing most of the fresh water on the planet. Rain occurs when two basic processes occur: Saturation and Coalescence.
Diagram of the Water Cycle. Credit: NASA Precipitation Education
Saturation:
This process occurs when “invisible” moisture in the air (water vapor) is forced to condense on microscopic particles (i.e. pollen and dust) to form tiny “visible” droplets. The amount of moisture in air is also commonly reported as relative humidity; which is the percentage of the total water vapor air can hold at a particular air temperature.
How much water vapor a parcel of air can contain before it becomes saturated (100% relative humidity) and forms into a cloud (a group of visible and tiny water and ice particles suspended above the Earth’s surface) depends on its temperature. Warmer air can contain more water vapor than cooler air before becoming saturated.
Coalescence:
Condensation occurs when the air is cooled down to its “dew point” temperature – the point at which it becomes saturated. Coalescence occurs when water droplets fuse to create larger water droplets (or when water droplets freeze onto an ice crystal) which is usually the result of air turbulence which forces collisions to occur.
As these larger water droplets descend, coalescence continues, so that drops become heavy enough to overcome air resistance and fall as rain. Rain is the primary source of freshwater for most areas of the world, providing suitable conditions for diverse ecosystems, as well as water for hydroelectric power plants and crop irrigation.
Image obtained by the Earth Observatory of the sun-glinted ocean and clouds. Credit: NASA
Measurement:
Rainfall is measured through the use of rain gauges. These gauges typically consist of two cylinders, one within the other, that fill with water. The inner cylinder fills first, with overflow entering the outer cylinder. Once the inner cylinder is filled, it is emptied and then filled with the remaining rainfall in the outer cylinder, producing a total estimate in millimeters or inches.
Other types of gauges include the popular wedge gauge, the tipping bucket rain gauge, and the weighing rain gauge. The most inexpensive option is a simple cylinder with a measuring stick, provided the cylinder is straight and the measuring stick is accurate. Any of these gauges can be made at home, with the right kind of knowledge.
Precipitation amounts are also estimated actively by weather radar, and passively by weather satellites. Examples of the latter include the Tropical Rainfall Measuring Mission (TRMM) satellite – a joint mission conducted by NASA and the Japanese Space Agency to monitor precipitation in the tropics – and NASA’s Global Precipitation Measurement (GPM).
Both of these mission employ microwave sensors to create precipitation estimates. Annual precipitation data is collected and monitored by NASA’s Earth Observatory (NEO), which creates detailed maps of global weather patterns (as well as heating and other meteorological factors).
A 3D map of the extra-tropical cyclone observed off the coast of Japan on March 10th, 2014, by GPM’s Dual-frequency Precipitation Radar. The colors indicate intensity of rainfall. Credit: JAXA/NASA
Climate Change:
Anthropocentric Climate Change, which includes Global Warming, is also causing changes in global precipitation patterns. This is due to the fact that increases in carbon dioxide emissions have led to increasing annual temperatures around the globe, leading to more evaporation and precipitation and more extreme weather events.
At latitudes north of 30°, precipitation has increased over the past century, while similarly declining over the tropics since the 1970s. And while there has been no consistent change on a global scale, regional variations have been pronounced. For instance, eastern portions of North and South America, northern Europe, and northern and central Asia have become wetter.
Other regions, such as the Sahel (between the Sahara desert and the Sudanian Savanna), the Mediterranean, southern Africa and parts of southern Asia have become drier. There has also been an increase in both the number of heavy rainstorms and droughts over many areas in the past century. In the tropics and subtropics, there has also been an increase in the prevalence of droughts since the 1970s.
Rain on Other Planets:
Despite what you might think, Earth is not the only planet where rain occurs. On other bodies in the Solar System, liquid precipitation takes place, though it rarely involves water. In fact, on Venus, rain regularly occurs, except that it involves sulfuric acid!
This acid rain is formed high in the atmosphere, where the wind speeds get up to 360 kilometers/hour (224 mph). However, once the droplets reach the lower atmosphere, they evaporate due to the extreme heat – over 460 °C or 860 °F. Hence, the rain never reaches the surface, which is extremely dry and molten.
On Saturn’s moon Titan, rain takes the form of methane. As evidence provided by the Cassini-Huygens mission has indicated, the moon has an active hydrological cycle. Except that Titan’s involves liquid hydrocarbons instead of water. As part of this cycle, liquid methane evaporates on the surface, accumulates in the atmosphere, and then returns to the surface as seasonal rains.
But it gets weirder! For instance, in recent years, scientists have obtained experimental evidence that indicates that Jupiter and Saturn may experience liquid helium rain. Due to the extreme pressure conditions that exist within the gas giants interior, these gases are compressed to the point where they take liquid form.
And then there’s what is known as “diamond rain”, which has been speculated to exist on all the gas giants. Essentially, Jupiter, Saturn, Uranus and Neptune all possess methane in their interiors. Due to the extreme pressure conditions, these hydrocarbons are compressed to the point that actual diamonds are believed to form. As such, diamond rain may actually exist in these gas/ice giants.
Last, but not least, there is the curious case of “Coronal Rain“, which takes place on the Sun. This phenomena occurs during a coronal mass ejection, where plasma cools after being ejected and falls back to the surface. Sometimes, these plasma droplets makes ‘splashes’ where they hit. And instead of falling straight down, the plasma rain appears to follow the path of the Sun’s invisible magnetic field lines.
Here on Earth, rain takes the form of water, and is an intrinsic part of our hydrological cycle. On other worlds, rain can take a different form, but still occupies much the same place in the planet’s cycle. Due to changing temperatures, saturation and coalescence, what goes up (in the form of vapor) must eventually come down.
Look up at the night sky, and what do you see? Space, glittering and gleaming in all its glory. Astronomically speaking, space is really quite close, lingering just on the other side of that thin layer we call an atmosphere. And if you think about it, Earth is little more than a tiny island in a sea of space. So it is quite literally all around us.
By definition, space is defined as being the point at which the Earth’s atmosphere ends, and the vacuum of space begins. But exactly how far away is that? How high do you need to travel before you can actually touch space? As you can probably imagine, with such a subjective definition, people tend to disagree on exactly where space begins.
Definition:
The first official definition of space came from the National Advisory Committee for Aeronautics (the predecessor to NASA), who decided on the point where atmospheric pressure was less than one pound per square foot. This was the altitude that airplane control surfaces could no longer be used, and corresponded to roughly 81 kilometers (50 miles) above the Earth’s surface.
The Bell X-1, in which Chuck Yeager “broke” the sound barrier in 1947. Credit: NASA
Any NASA test pilot or astronaut who crosses this altitude is awarded their astronaut wings. Shortly after that definition was passed, the aerospace engineer Theodore von Kármán calculated that above an altitude of 100 km, the atmosphere would be so thin that an aircraft would need to be traveling at orbital velocity to derive any lift.
This altitude was later adopted as the Karman Line by the World Air Sports Federation (Fédération Aéronautique Internationale, FAI). And in 2012, when Felix Baumgartner broke the record for the highest freefall, he jumped from an altitude of 39 kilometers (24.23 mi), less than halfway to space (according to NASA’s definition).
By the same token, space is often defined as beginning at the lowest altitude at which satellites can maintain orbits for a reasonable time – which is approximately 160 kilometers (100 miles) above the surface. These varying definitions are complicated when one takes the definition of the word “atmosphere” into account.
Earth’s Atmosphere:
When we talk about Earth’s atmosphere, we tend to think of the region where air pressure is still high enough to cause air resistance, or where the air is simply thick enough to breath. But in truth, Earth’s atmosphere is made up of five main layers – the Troposphere, the Stratosphere, the Mesosphere, the Thermosphere, and the Exosphere – the latter of which extend pretty far out into space.
Space Shuttle Endeavor silhouetted against Earth’s atmosphere. The orange layer is the troposphere, the white layer is the stratosphere and the blue layer the mesosphere. Credit: NASAThe Thermosphere, the second highest layer of the atmosphere, extends from an altitude of about 80 km (50 mi) up to the thermopause, which is at an altitude of 500–1000 km (310–620 mi). The lower part of the thermosphere, – from 80 to 550 kilometers (50 to 342 mi) – contains the ionosphere, which is so named because it is here in the atmosphere that particles are ionized by solar radiation.
Hence, this is where the phenomena known as Aurora Borealis and Aurara Australis are known to take place. The International Space Station also orbits in this layer, between 320 and 380 km (200 and 240 mi), and needs to be constantly boosted because friction with the atmosphere still occurs.
The outermost layer, known as the exosphere, extends out to an altitude of 10,000 km (6214 mi) above the planet. This layer is mainly composed of extremely low densities of hydrogen, helium and several heavier molecules (nitrogen, oxygen, CO²). The atoms and molecules are so far apart that the exosphere no longer behaves like a gas and the particles constantly escape into space.
It is here that Earth’s atmosphere truly merges with the emptiness of outer space, where there is no atmosphere. Hence why the majority of Earth’s satellites orbit within this region. Sometimes, the Aurora Borealis and Aurora Australis occur in the lower part of the exosphere, where they overlap into the thermosphere. But beyond that, there is no meteorological phenomena in this region.
Interplanetary vs. Interstellar:
Another important distinction when discussing space is the difference between that which lies between planets (interplanetary space) and that which lies between star systems (interstellar space) in our galaxy. But of course, that’s just the tip of the iceberg when it comes to space.
If one were to cast the net wider, there is also the space which lies between galaxies in the Universe (intergalactic space). In all cases, the definition involves regions where the concentration of matter is significantly lower than in other places – i.e. a region occupied centrally by a planet, star or galaxy.
In addition, in all three definitions, the measurements involved are beyond anything that we humans are accustomed to dealing with on a regular basis. Some scientists believe that space extends infinitely in all directions, while others believe that space is finite, but is unbounded and continuous (i.e. has no beginning and end).
In other words, there’s a reason they call it space – there’s just so much of it!
Exploration:
The exploration of space (that is to say, that which lies immediately beyond Earth’s atmosphere) began in earnest with what is known as the “Space Age“, This newfound age of exploration began with the United States and Soviet Union setting their sights on placing satellites and crewed modules into orbit.
The first major event of the Space Age took place on October 4th, 1957, with the launch ofSputnik 1 by the Soviet Union – the first artificial satellite to be launched into orbit. In response, then-President Dwight D. Eisenhower signed the National Aeronautics and Space Act on July 29th, 1958, officially establishing NASA.
Photograph of a Russian technician putting the finishing touches on Sputnik 1, humanity’s first artificial satellite. Credit: NASA/Asif A.
Immediately, NASA and the Soviet space program began taking the necessary steps towards creating manned spacecraft. By 1959, this competition resulted in the creation of the Soviet Vostok program and NASA’s Project Mercury. In the case of Vostok, this consisted of developing a space capsule that could be launched aboard an expendable carrier rocket.
Along with numerous unmanned tests, and a few using dogs, six Soviet pilots were selected by 1960 to be the first men to go into space. On April 12th, 1961, Soviet cosmonaut Yuri Gagarin was launched aboard the Vostok 1spacecraft from the Baikonur Cosmodrome, and thus became the fist man to go into space (beating American Alan Shepard by just a few weeks).
On June 16th, 1963, Valentina Tereshkova was sent into orbit aboard the Vostok 6 craft (which was the final Vostok mission), and thus became the first woman to go into space. Meanwhile, NASA took over Project Mercury from the US Air Force and began developing their own crewed mission concept.
Yury Gagarin before a space flight aboard the Vostok spacecraft. April 12, 1961 Credit: RIA Novosti
Designed to send a man into space using existing rockets, the program quickly adopted the concept of launching ballistic capsules into orbit. The first seven astronauts, nicknamed the “Mercury Seven“, were selected from from the Navy, Air Force and Marine test pilot programs.
On May 5th, 1961, astronaut Alan Shepard became the first American in space aboard the Freedom 7 mission. Then, on February 20th, 1962, astronaut John Glenn became the first American to be launched into orbit by an Atlas launch vehicle as part of Friendship 7. Glenn completed three orbits of planet Earth, and three more orbital flights were made, culminating in L. Gordon Cooper’s 22-orbit flight aboard Faith 7, which flew on May 15th and 16th, 1963.
In the ensuing decades, both NASA and Soviets began to develop more complex, long-range crewed spacecraft. Once the “Race to the Moon” ended with the successful landing of Apollo 11 (followed by several more Apollo missions), the focus began to shift to establishing a permanent presence in space.
For the Russians, this led to the continued development of space station technology as part of the Salyut program. Between 1972 and 1991, they attempted to orbit seven separate stations. However, technical failures and a failure in one rocket’s second stage boosters caused the first three attempts after Salyut 1 to fail or result in the station’s orbits decaying after a short period.
Skylab, America’s First manned Space Station. Photo taken by departing Skylab 4 crew in Feb. 1974. Credit: NASA
However, by 1974, the Russians managed to successfully deploy Salyut 4, followed by three more stations that would remain in orbit for periods of between one and nine years. While all of the Salyuts were presented to the public as non-military scientific laboratories, some of them were actually covers for the military Almaz reconnaissance stations.
NASA also pursued the development of space station technology, which culminated in May of 1973 with the launch of Skylab, which would remain America’s first and only independently-built space station. During deployment, Skylab suffered severe damage, losing its thermal protection and one of its solar panels.
This required the first crew to rendezvous with the station and conduct repairs. Two more crews followed, and the station was occupied for a total of 171 days during its history of service. This ended in 1979 with the downing of the station over the Indian Ocean and parts of southern Australia.
By 1986, the Soviets once again took the lead in the creation of space stations with the deployment of Mir. Authorized in February 1976 by a government decree, the station was originally intended to be an improved model of the Salyut space stations. In time, it evolved into a station consisting of multiple modules and several ports for crewed Soyuz spacecraft and Progress cargo spaceships.
The Mir Space Station and Earth limb observed from the Orbiter Endeavour during NASA’s STS-89 mission in 1998. Credit: NASA
The core module was launched into orbit on February 19th, 1986; and between 1987 and 1996, all of the other modules would be deployed and attached. During its 15-years of service, Mir was visited by a total of 28 long-duration crews. Through a series of collaborative programs with other nations, the station would also be visited by crews from other Eastern Bloc nations, the European Space Agency (ESA), and NASA.
After a series of technical and structural problems caught up with the station, the Russian government announced in 2000 that it would decommission the space station. This began on Jan. 24th, 2001, when a Russian Progress cargo ship docked with the station and pushed it out of orbit. The station then entered the atmosphere and crashed into the South Pacific.
By 1993, NASA began collaborating with the Russians, the ESA and the Japan Aerospace Exploration Agency (JAXA) to create the International Space Station (ISS). Combining NASA’s Space Station Freedom project with the Soviet/Russian Mir-2 station, the European Columbus station, and the Japanese Kibo laboratory module, the project also built on the Russian-American Shuttle-Mir missions (1995-1998).
With the retirement of the Space Shuttle Program in 2011, crew members have been delivered exclusively by Soyuz spacecraft in recent years. Since 2014, cooperation between NASA and Roscosmos has been suspended for most non-ISS activities due to tensions caused by the situation in the Ukraine.
However, in the past few years, indigenous launch capability has been restored to the US thanks to companies like SpaceX, United Launch Alliance, and Blue Origin stepping in to fill the void with their private fleet of rockets.
The ISS has been continuously occupied for the past 15 years, having exceeded the previous record held by Mir; and has been visited by astronauts and cosmonauts from 15 different nations. The ISS program is expected to continue until at least 2020, but may be extended until 2028 or possibly longer, depending on the budget environment.
As you can clearly see, where our atmosphere ends and space begins is the subject of some debate. But thanks to decades of space exploration and launches, we have managed to come up with a working definition. But whatever the exact definition is, if you can get above 100 kilometers, you have definitely earned your astronaut wings!
Continuing with our “Definitive Guide to Terraforming“, Universe Today is happy to present to our guide to terraforming Jupiter’s Moons. Much like terraforming the inner Solar System, it might be feasible someday. But should we?
Fans of Arthur C. Clarke may recall how in his novel, 2010: Odyssey Two (or the movie adaptation called 2010: The Year We Make Contact), an alien species turned Jupiter into a new star. In so doing, Jupiter’s moon Europa was permanently terraformed, as its icy surface melted, an atmosphere formed, and all the life living in the moon’s oceans began to emerge and thrive on the surface.
As we explained in a previous video (“Could Jupiter Become a Star“) turning Jupiter into a star is not exactly doable (not yet, anyway). However, there are several proposals on how we could go about transforming some of Jupiter’s moons in order to make them habitable by human beings. In short, it is possible that humans could terraform one of more of the Jovians to make it suitable for full-scale human settlement someday.
As a gas giant (or ice giant), Neptune has no solid surface. In fact, the blue-green disc we have all seen in photographs over the years is actually a bit of an illusion. What we see is actually the tops of some very deep gas clouds, which in turn give way to water and other melted ices that lie over an approximately Earth-size core made of silicate rock and a nickel-iron mix. If a person were to attempt to stand on Neptune, they would sink through the gaseous layers.
As they descended, they would experience increased temperatures and pressures until they finally touched down on the solid core itself. That being said, Neptune does have a surface of sorts, (as with the other gas and ice giants) which is defined by astronomers as being the point in the atmosphere where the pressure reaches one bar. Because of this, Neptune’s surface is one of the most active and dynamic places in entire the Solar System.
New Horizons’ historic journey to Pluto and beyond continues to provide surprises. As data from the spacecraft’s close encounter with Pluto and its moons arrives at Earth, scientists are piecing together an increasingly intriguing picture of the dwarf planet. The latest discovery is centred around Pluto’s atmosphere, and what are called ‘atmospheric gravity waves.’
Atmospheric gravity waves are a different phenomenon than the gravity waves that were detected for the first time in February, 2016. Those gravity waves are ripples in the fabric of space time, first predicted by Albert Einstein back in 1916. After years of searching, the LIGO instrument detected gravity waves that resulted from two black holes colliding. The discovery of what you might call ‘Einsteinian Gravity Waves’ may end up revolutionizing astronomy.
New Horizons has revealed surprise after surprise in its study of Pluto. Its atmosphere has turned out to be much more complex than anybody expected. It’s composed of 90% nitrogen, with extensive haze layers. Scientists have discovered that Pluto’s atmosphere can vary in brightness depending on viewpoint and illumination, while the vertical structure of the layered haze remains unchanged.
Scientists studying the New Horizons’ data think that atmospheric gravity waves, also called buoyancy waves, are responsible. Atmospheric gravity waves are known to exist on only two other planets; Earth and Mars. They are typically caused by wind flowing over obstructions like mountain ranges.
The layers in Pluto’s atmosphere, and their varying brightness, are most easily seen when they are backlit by the Sun. This was the viewpoint New Horizons had when it captured these images on its departure from Pluto on July 14, 2015. The spacecraft’s Long Range Reconnaissance Imager (LORRI) captured them, using time intervals of 2 to 5 hours. What they show is the brightness of the layers changing by 30% without any change in their height above the surface of the planet.
LORRI, as its name suggests, is a long range image capture instrument. It also captures high resolution geologic data, and was used to map Pluto’s far side. The principal investigator for LORRI is Andy Cheng, from the Applied Physics Laboratory at Johns Hopkins University, in Maryland. “Pluto is simply amazing,” said Andy Cheng. “When I first saw these images and the haze structures that they reveal, I knew we had a new clue to the nature of Pluto’s hazes. The fact that we don’t see the haze layers moving up or down will be important to future modelling efforts.”
Overall, Pluto and its system of moons has turned out to be a much more dynamic place than previously thought. A geologically active landscape, possible ice volcanoes, eroding cliffs made of methane ice, and more, have woken us up to Pluto’s complexity. But its atmosphere has turned out to be just as complex and puzzling.
New Horizons has departed the Pluto system now, and is headed for the Kuiper Belt. The Kuiper Belt is considered a relic of the early Solar System. New Horizons will visit another icy world there, and hopefully continue on to the edge of the heliosphere, the same way the Voyage probes have. New Horizons has enough energy to last until approximately the mid-2030’s, if all goes well.
Here on Earth, we’re always concerned with the weather.
“OK Google, am I going to need an umbrella tomorrow?”
[Google] No, rain is not expected tomorrow in Curtney. The forecast is 20 degrees and partly cloudy.
Uh, it’s pronounced “Courtenay”.
Fine, what if I lived on the Moon? OK Google, am I going to need an umbrella tomorrow on the Moon?
[Google] …
Let’s take Google’s silence for uncertainty.
The names of geological features on the Moon sure evoke mental images of weather. There’s the Ocean of Storms, also known as Oceanus Procellarum, or the Ocean of Clouds – aka Mare Nubium. In fact, most of the regions of the Moon are named after oceans. That’s got to count for something, right?
Many of the features of the moon were thought to be oceans. Credit: NASA
They got these names because the early astronomers thought they were seeing actual oceans on the Moon. They imagined vast seas, where heroic 6-legged creepy bug people plied the icy waves seeking fame, fortune and lunar plunder. I don’t know, like gold cheese or something. Seriously, they were making a lot of this stuff up until telescopes were invented.
But when the NASA astronauts finally set foot on the Moon, they knew they wouldn’t need to pack their snorkeling gear because there weren’t any oceans on the Moon, or really any atmosphere. The Moon is almost as dead and lifeless as space itself.
The storms we see battering the astronauts on every Mars science fiction story just can’t happen on the Moon because there’s no air there.
There’s an ongoing lethal radiation solar wind blowing from the Sun and deep space, but nothing that you’d be able to windsurf too.
So why isn’t there an atmosphere on the Moon? It all comes down to gravity. The Moon has about 1% of the mass of the Earth, which means that it doesn’t have enough gravity to hold onto any gas atmosphere. Anything that it did have would have been blown away by the solar wind billions of years ago.
We did a whole episode on what it would take to terraform the Moon, and it turns out you’d need to constantly replenish the atmosphere.
In fact, this is one of the reasons why the Martian atmosphere is so thin. It was probably thicker in the past, but the solar winds stripped off all the lighter atmosphere long ago. Now it’s just 1% the thickness of the Earth’s atmosphere.
Now, I’ve said that the Moon has almost no atmosphere. But almost no means partly yes. There is in fact an incredibly thin atmosphere surrounding the Moon which measures about a hundred trillionth the thickness of the Earth’s atmosphere.
There are a few sources of this atmosphere. First there’s volcanic outgassing that comes from the Moon. this contributes a little helium and radon. Then there’s the constant micrometeorite bombardment that kicks up pulverized lunar regolith.
Lunar sunrise sketches drawn by Commander E. A. Cernan during the Apollo 17 mission. Credit: NASA
But perhaps the strangest atmospheric feature is a storm that does rage across the surface of the Moon right at the terminator, the exact line between the Moon’s day side and its night side. It turns out the day side of the Moon is positively charged, and the night side is negatively charged.
As the terminator moves, the polarity of the dust flips and it drives it sideways. In fact, the astronauts who walked on the Moon actually reported seeing this. They saw bands or twilight rays in the sky around lunar sunrise/sunset.
Without a thick atmosphere, the surface of the Moon just doesn’t have any appreciable weather and definitely doesn’t have storms like we have on Earth. Mark Watney will need some other reason than weather to be stuck behind on the Moon.
Welcome back to our ongoing series, “The Definitive Guide To Terraforming”! We continue with a look at the Moon, discussing how it could one day be made suitable for human habitation.
Ever since the beginning of the Space Age, scientists and futurists have explored the idea of transforming other worlds to meet human needs. Known as terraforming, this process calls for the use of environmental engineering techniques to alter a planet or moon’s temperature, atmosphere, topography or ecology (or all of the above) in order to make it more “Earth-like”. As Earth’s closest celestial body, the Moon has long been considered a potential site.
All told, colonizing and/or terraforming the Moon would be comparatively easy compared to other bodies. Due to its proximity, the time it would take to transport people and equipment to and from the surface would be significantly reduced, as would the costs of doing so. In addition, it’s proximity means that extracted resources and products manufactured on the Moon could be shuttled to Earth in much less time, and a tourist industry would also be feasible.
Astronomers using the Hubble Space Telescope have measured the rotation rate of an extreme exoplanet 2M1207b by observing the varied brightness in its atmosphere. This is the first measurement of the rotation of a massive exoplanet using direct imaging.
This is a composite image of the brown dwarf object 2M1207 (blue-white) and the planet 2M1207b, seen in red, located 170 light years from Earth in the constellation Centaurus. The photo is based on three near-infrared exposures with the taken with the 8.2-m VLT Yepun telescope at the ESO Paranal Observatory. Credit: ESO
Little by little we’re coming to know at least some of the 2,085 exoplanets discovered to date more intimately despite their great distances and proximity to the blinding light of their host stars. 2M1207b is about four times more massive than Jupiter and dubbed a “super-Jupiter”. Super-Jupiters fill the gap between Jupiter-mass planets and brown dwarf stars. They can be up to 80 times more massive than Jupiter yet remain nearly the same size as that planet because gravity compresses the material into an ever denser, more compact sphere.
2M1207b lies 170 light years from Earth and orbits a brown dwarfat a distance of 5 billion miles. By contrast, Jupiter is approximately 500 million miles from the sun. You’ll often hear brown dwarfs described as “failed stars” because they’re not massive enough for hydrogen fusion to fire up in their cores the way it does in our sun and all the rest of the main sequence stars.
Researchers used Hubble’s exquisite resolution to precisely measure the planet’s brightness changes as it spins and nailed the rotation rate at 10 hours, virtually identical to Jupiter’s. While it’s fascinating to know a planet’s spin, there’s more to this extraordinary exoplanet. Hubble data confirmed the rotation but also showed the presence of patchy, “colorless” (white presumably) cloud layers. While perhaps ordinary in appearance, the composition of the clouds is anything but.
Exoplanet 2M1207 b with the Solar System planet Jupiter for comparison. Although four times more massive than the Jovian planet, gravity compresses its matter to keep it relatively small. Credit: Wikipedia / Aldaron
The planet appears bright in infrared light because it’s young (about 10 million years old) and still contracting, releasing gravitational potential energy that heats it from the inside out. All that extra heat makes 2M1207b’s atmosphere hot enough to form “rain” clouds made of vaporized rock. The rock cools down to form tiny particles with sizes similar to those in cigarette smoke. Deeper into the atmosphere, iron droplets are forming and falling like rain, eventually evaporating as they enter the lower levels of the atmosphere.
“So at higher altitudes it rains glass, and at lower altitudes it rains iron,” said Yifan Zhou of the University of Arizona, lead author on the research paper in a recent Astrophysical Journal. “The atmospheric temperatures are between about 2,200 to 2,600 degrees Fahrenheit.” Every day’s a scorcher on 2M1207b.
Both Jupiter and Saturn also emit more heat than they receive from the sun because they too are still contracting despite being 450 times older. The bigger you are, the slower you chill.
Illustration of the extrasolar planet 2M1207b (foreground) orbiting a brown dwarf. Both shine brightly in infrared light. Credits: NASA, ESA, and G. Bacon/STScI
All the planets in our Solar System possess only a fraction of the mass of the Sun. Even mighty Jove is a thousand times less massive. But Mr. Super-Jupiter’s a heavyweight compared to its brown dwarf host, being just 5-7 times less massive. While Jupiter and the rest of the planets formed by the accretion of dust and rocks within a clumpy disk of material surrounding the early Sun, it’s thought 2M1207b and its companion may have formed throughout the gravitational collapse of a pair of separate disks.
This super-Jupiter will an ideal target for the James Webb Space Telescope, a space observatory optimized for the infrared scheduled to launch in 2018. With its much larger mirror — 21-feet (6.5-meters) — Webb will help astronomers better determine the exoplanet’s atmospheric composition and created more detailed maps from brightness changes.
Teasing out the details of 2M1207b’s atmosphere and rotation introduces us to a most alien world the likes of which never evolved in our own Solar System. I feel like I’m aboard the Starship Enterprise visiting far-flung worlds. Only this is better. It’s real.
Have you ever looked up on a clear night and noticed there’s a complete ring around the Moon? In fact, if you look closely, the ring can have a rainbow appearance, with bright spots on either side, or above and below. What’s going on with the Moon and the atmosphere to cause this effect?
This ring surrounding the Moon is caused by the refraction of Moonlight (which is really reflected sunlight, of course) through ice crystals suspended in the upper atmosphere between 5-10 km in altitude. It doesn’t have to be winter, since the cold temperatures at high altitudes are below freezing any time of the year. Generally they’re seen with cirrus clouds; the thin, wispy clouds at high altitude.
The ice crystals themselves have a very consistent hexagonal shape, which means that any light passing through them will always refract light – or bend – at the same angle.
Path of rays in a hexagonal prism” by donalbein – Own work. Licensed under CC BY-SA 2.5 via Commons.Moonlight passes through one facet of the ice crystal, and is then refracted back out at exactly the angle of 22-degrees.
Of course, the atmosphere is filled with an incomprehensible number of crystals, all refracting moonlight off in different directions. But at any moment, a huge number happen to be in just the right position to be refracting light towards your eyes. You just aren’t in a position to see all the other refracted light. In fact, everyone sees their own private halo, because you’re only seeing the crystals that happen to be aligning the light for your specific location. Someone a few meters beside you is seeing their own private version of the halo – just like a rainbow.
A halo rings the bright moon and planet Jupiter (left of moon) Credit: Bob King
The size of the ring is most commonly 22-degrees. This is about the same size as your open hand on your outstretched arm. The Moon itself, for comparison, is the size of your smallest nail when you hold out your hand.
The 22-degree size corresponds to the refraction angle of moonlight.
We see a rainbow because the different colors are refracted at slightly different angles. This is exactly what happens with a rainbow. The moonlight is broken up into its separate colors because they all refract at different angles, and so you see the colors split up like a rainbow.
Lunar halo with rainbow. Photo credit: Gustav Sanchez.Moon dogs (or “mock moons”) are seen as bright spots that can appear on either side of the Moon, when the Moon is closer to the horizon, and at its fullest. These are located on either side of the lunar ring, parallel to the horizon.
In certain conditions, especially in the Arctic, where the ice crystals can be close to the surface, you can get a moon pillar. The light from the Moon reflects off the ice crystals near the surface, creating a glow near the horizon. This is a Sun pillar (not a moon pillar), but it’s the same general idea. Photo credit: Mary Spicer.
Want to see more? Here’s a great lunar halo photo from NASA’s APOD. And here’s more info from Earth and Sky.
![Space Shuttle Endeavour sillouetted against the atmosphere. The orange layer is the troposphere, the white layer is the stratosphere and the blue layer the mesosphere.[1] (The shuttle is actually orbiting at an altitude of more than 320 km (200 mi), far above all three layers.) Credit: NASA](https://www.universetoday.com/wp-content/uploads/2012/03/Endeavour_silhouette_STS-130.jpg)
