Earth is an Exoplanet to Aliens. This is What They’d See

The study of exoplanets has matured considerably in the last ten years. During this time, the majority of the over 4000 exoplanets that are currently known to us were discovered. It was also during this time that the process has started to shift from the process of discovery to characterization. What’s more, next-generation instruments will allow for studies that will reveal a great deal about the surfaces and atmospheres of exoplanets.

This naturally raises the question: what would a sufficiently-advanced species see if they were studying our planet? Using multi-wavelength data of Earth, a team of Caltech scientists was able to construct a map of what Earth would look like to distant alien observers. Aside from addressing the itch of curiosity, this study could also help astronomers reconstruct the surface features of “Earth-like” exoplanets in the future.

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AI Could Help the Europa Clipper Mission Make New Discoveries!

In 2023, NASA plans to launch the Europa Clipper mission, a robotic explorer that will study Jupiter’s enigmatic moon Europa. The purpose of this mission is to explore Europa’s ice shell and interior to learn more about the moon’s composition, geology, and interactions between the surface and subsurface. Most of all, the purpose of this mission is to shed light on whether or not life could exist within Europa’s interior ocean.

This presents numerous challenges, many of which arise from the fact that the Europa Clipper will be very far from Earth when it conducts its science operations. To address this, a team of researchers from NASA’s Jet Propulsion Laboratory (JPL) and Arizona State University (ASU) designed a series of machine-learning algorithms that will allow the mission to explore Europa with a degree of autonom.

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A Star’s Outburst is Releasing Organic Molecules Trapped in the ice Around it

According to widely-accepted theories, the Solar System formed roughly 4.6 billion years ago from a massive cloud of dust and gas (aka. Nebular Theory). This process began when the nebula experienced a gravitational collapse in the center that became our Sun. The remaining dust and gas formed a protoplanetary disk that (over time) accreted to form the planets.

However, scientists remain unsure about when organic molecules first appeared in our Solar System. Luckily, a new study by an international team of astronomers may be able to help answer that question. Using the Atacama Large Millimeter-submillimeter Array (ALMA), the team detected complex organic molecules around the young star V883 Ori, which could someday lead to the emergence of life in that system.

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Are There Enough Chemicals on Icy Worlds to Support Life?

For decades, scientists have believed that there could be life beneath the icy surface of Jupiter’s moon Europa. Since that time, multiple lines of evidence have emerged that suggest that it is not alone. Indeed, within the Solar System, there are many “ocean worlds” that could potentially host life, including Ceres, Ganymede, Enceladus, Titan, Dione, Triton, and maybe even Pluto.

But what if the elements for life as we know it are not abundant enough on these worlds? In a new study, two researchers from the Harvard Smithsonian Center of Astrophysics (CfA) sought to determine if there could in fact be a scarcity of bioessential elements on ocean worlds. Their conclusions could have wide-ranging implications for the existence of life in the Solar System and beyond, not to mention our ability to study it.

The study, titled “Is extraterrestrial life suppressed on subsurface ocean worlds due to the paucity of bioessential elements?” recently appeared online. The study was led by Manasvi Lingam, a postdoctoral fellow at the Institute for Theory and Computation (ITC) at Harvard University and the CfA, with the support of Abraham Loeb – the director of the ITC and the Frank B. Baird, Jr. Professor of Science at Harvard.

Artist’s depiction of a watery exoplanet orbiting a distant red dwarf star. Credit: CfA

In previous studies, questions on the habitability of moons and other planets have tended to focus on the existence of water. This has been true when it comes to the study of planets and moons within the Solar System, and especially true when it comes the study of extra-solar planets. When they have found new exoplanets, astronomers have paid close attention to whether or not the planet in question orbits within its star’s habitable zone.

This is key to determining whether or not the planet can support liquid water on its surface. In addition, astronomers have attempted to obtain spectra from around rocky exoplanets to determine if water loss is taking place from its atmosphere, as evidenced by the presence of hydrogen gas. Meanwhile, other studies have attempted to determine the presence of energy sources, since this is also essential to life as we know it.

In contrast, Dr. Lingam and Prof. Loeb considered how the existence of life on ocean planets could be dependent on the availability of limiting nutrients (LN). For some time, there has been considerable debate as to which nutrients would be essential to extra-terrestrial life, since these elements could vary from place to place and over timescales. As Lingam told Universe Today via email:

“The mostly commonly accepted list of elements necessary for life as we know it comprises of hydrogen, oxygen, carbon, nitrogen and sulphur. In addition, certain trace metals (e.g. iron and molybdenum) may also be valuable for life as we know it, but the list of bioessential trace metals is subject to a higher degree of uncertainty and variability.”

Artist rendering showing an interior cross-section of the crust of Enceladus, which shows how hydrothermal activity may be causing the plumes of water at the moon’s surface. Credits: NASA-GSFC/SVS, NASA/JPL-Caltech/Southwest Research Institute

For their purposes, Dr. Lingam and Prof. Loeb created a model using Earth’s oceans to determine how the sources and sinks – i.e. the factors that add or deplete LN elements into oceans, respectively – could be similar to those on ocean worlds. On Earth, the sources of these nutrients include fluvial (from rivers), atmospheric and glacial sources, with energy being provided by sunlight.

Of these nutrients, they determined that the most important would be phosphorus, and examined how abundant this and other elements could be on ocean worlds, where conditions as vastly different. As Dr. Lingam explained, it is reasonable to assume that on these worlds, the potential existence of life would also come down to a balance between the net inflow (sources) and net outflow (sinks).

“If the sinks are much more dominant than the sources, it could indicate that the elements would be depleted relatively quickly. In other to estimate the magnitudes of the sources and sinks, we drew upon our knowledge of the Earth and coupled it with other basic parameters of these ocean worlds such as the pH of the ocean, the size of the world, etc. known from observations/theoretical models.”

While atmospheric sources would not be available to interior oceans, Dr. Lingam and Prof. Loeb considered the contribution played by hydrothermal vents. Already, there is abundant evidence that these exist on Europa, Enceladus, and other ocean worlds. They also considered abiotic sources, which consist of minerals leached from rocks by rain on Earth, but would consist of the weathering of rocks by these moons’ interior oceans.

Artist’s rendering of possible hydrothermal activity that may be taking place on and under the seafloor of Enceladus. Credit: NASA/JPL

Ultimately, what they found was that, unlike water and energy, limiting nutrients might be in limited supply when it comes to ocean worlds in our Solar System:

“We found that, as per the assumptions in our model, phosphorus, which is one of the bioessential elements, is depleted over fast timescales (by geological standards) on ocean worlds whose oceans are neutral or alkaline in nature, and which possess hydrothermal activity (i.e. hydrothermal vent systems at the ocean floor). Hence, our work suggests that life may exist in low concentrations globally in these ocean worlds (or be present only in local patches), and may therefore not be easily detectable.”

This naturally has implications for missions destined for Europa and other moons in the outer Solar System. These include the NASA Europa Clipper mission, which is currently scheduled to launch between 2022 and 2025. Through a series of flybys of Europa, this probe will attempt to measure biomarkers in the plume activity coming from the moon’s surface.

Similar missions have been proposed for Enceladus, and NASA is also considering a “Dragonfly” mission to explore Titan’s atmosphere, surface and methane lakes. However, if Dr. Lingam and Prof. Loeb’s study is correct, then the chances of these missions finding any signs of life on an ocean world in the Solar System are rather slim. Nevertheless, as Lingam indicated, they still believe that such missions should be mounted.

Artist’s concept of a Europa Clipper mission. Credit: NASA/JPL

“Although our model predicts that future space missions to these worlds might have low chances of success in terms of detecting extraterrestrial life, we believe that such missions are still worthy of being pursued,” he said. “This is because they will offer an excellent opportunity to: (i) test and/or falsify the key predictions of our model, and (ii) collect more data and improve our understanding of ocean worlds and their biogeochemical cycles.”

In addition, as Prof. Loeb indicated via email, this study was focused on “life as we know it”. If a mission to these worlds did find sources of extra-terrestrial life, then it would indicate that life can arise from conditions and elements that we are not familiar with. As such, the exploration of Europa and other ocean worlds is not only advisable, but necessary.

“Our paper shows that elements that are essential for the ‘chemistry-of-life-as-we-know-it’, such as phosphorous, are depleted in subsurface oceans,” he said. “As a result, life would be challenging in the oceans suspected to exist under the surface ice of Europa or Enceladus. If future missions confirm the depleted level of phosphorous but nevertheless find life in these oceans, then we would know of a new chemical path for life other than the one on Earth.”

In the end, scientists are forced to take the “low-hanging fruit” approach when it comes to searching for life in the Universe . Until such time that we find life beyond Earth, all of our educated guesses will be based on life as it exists here. I can’t imagine a better reason to get out there and explore the Universe than this!

Further Reading: arXiv

How Badly Will Humanity Freak Out if We Discover Alien Life?

The discovery of alien life is one of those things that everyone thinks about at some point. Hollywood has made their version of first contact very clear: huge alien vessels appear over Earth’s cities, panic ensues, and Will Smith saves the day with a Windows 3.1 virus. It’s lots of fun—and who knows?—it may end up being accurate. (Not the Windows 3.1 part.) But sci-fi books and movies aside, what do we really know about our attitude to the discovery of alien life?

We have an organization (SETI) dedicated to detecting the presence of alien civilizations, and we have a prominent scientist (Stephen Hawking) warning against advertising our own presence. Those represent the extremes—actively seeking out alien life vs. hiding from it—but what is the collective attitude towards the discovery of alien life? Scientists at Arizona State University (ASU) have studied that issue and detailed their results in a new study published in the journal Frontiers of Psychology.

The team of scientists tried to gauge people’s reactions to the discovery of alien life in three separate parts of their study. In the first case, they examined media reports of past announcements about the discovery of alien life, for example the announcement in 1996 that evidence of microbial life had been found in a Martian metorite.

Secondly, they asked a sample of over 500 people what their own reactions, and the reactions of the rest of humanity, would be to the hypothetical announcement of alien life.

Thirdly, the 500 people were split into two groups. Half were asked to read and respond to a real newspaper story announcing the discovery of fossilized Martian microbial life. The other half were asked to read and respond to a newspaper article announcing the creation of synthetic life by Craig Venter.

Martian meteorite ALH84001 was found in Antarctica in 1984 by a group of meteorite hunters from the US. Scientists who studied it suggested that it contained evidence of ancient Martian microbial life. Image: By Jstuby at English Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=47556214

In all three cases the life was microbial in nature. Microbial life is the simplest life form, so it should be what we expect to find. This is certainly true in our own Solar System, since the existence of any other intelligent life has been ruled out here, while microbial life has not.

Also, in all three cases, the language of the respondents and the language in the media reports was analyzed for positive and negative words. A specialized piece of software called Linguistic Inquiry and Word Count (LIWC) was used. It’s text-analysis software that scans written language and identifies instances of words that reflect positive affect, negative affect, reward, or risk. (You can try LIWC here for fun, if you like.)

Electron microscope images of the Martian meteorite ALH84001 showed chain-like structures that resembled living structures. Image: NASA

Analyzing Media Reports

The media reports used in the study were all from what the team considers reputable journalism outlets like The New York Times and Science Magazine. The reports were about things like unidentified signals from space that could have been alien in nature, fossilized microbial remains in meteorites, and the discovery of exoplanets in the habitable zones of other solar systems. There were 15 articles in total.

The authors of the study wanted to find out how people would react to the discovery of alien life, and to the discovery of potentially habitable exoplanets which might harbor life. In this artist’s illustration, exoplanets orbit a young, red dwarf star. Credit: NASA/JPL-Caltec

Overall, the study showed that language in media reports about alien life was more positive than negative, and emphasized reward rather than risk. So people generally find the potential of alien life to be a positive thing and something to be looked forward to. However, this part of the study showed something else: People were more positively disposed towards news of alien life that was microbial than they were towards alien life that could be present on exoplanets, where, presumably, it might be more than merely microbial. So, microbes we can handle, but something more advanced and a little doubt starts to creep in.

Reactions to Hypothetical Announcements of Alien Life

This part of the study aimed to assess people’s beliefs regarding how both they as individuals—and humanity as a whole—might react to the discovery of alien microbial life. The same LIWC software was used to analyze the written responses of the 500 people in the sample group.

The results were similar to the first part of the study, at least for the individuals themselves. Positive affect was more predominant than negative aspect, and words reflecting reward were more predominant than words reflecting risk. This probably isn’t surprising, but the study did show something more interesting.

When participants were asked about how the rest of humanity would respond to the announcement of alien life, the response was different. While positive language still outweighed negative language, and reward still outweighed risk, the differences weren’t as pronounced as they were for individuals. So people seem to think that others won’t be looking forward to the discovery of alien life as much as they themselves do.

Actual Reactions to the Discovery of Extraterrestrial Life

This is hard to measure since we haven’t actually discovered any yet. But there have been times when we thought we might have.

In this part of the study, the group of 500 respondents was split into two groups of 250. The first was asked to read an actual 1996 New York Times article announcing the discovery of fossilized microbes in the Martian meteorite. The second group was asked to read a New York Times article from 2010 announcing the creation of life by Craig Venter. The goal was to find out if the positive bias towards the discovery of microbial life was specific to microbial life, or to scientific advancements overall.

Saturn’s moon Enceladus could harbor microbial life in the warm salty water thought to exist under its frozen surface. Respondents in the study seemed to like that possibility. Credits: NASA/JPL-Caltech/Space Science Institute

This part of the study found the same emphasis on positive affect over negative affect, and reward over risk. This held true in both cases: the Martian microbial life article, and the artificially created life article. The type of article played a minor role in people’s responses. Results were slightly more positive towards the Martian life story than the artificial life story.

Overall, this study shows that people seem positively disposed towards the discovery of alien life. This is reflected in media coverage, people’s personal responses, and people’s expectations of how others would react.

This is really just the tip of the iceberg, though. As the authors say in their study, this is the first empirical attempt to understand any of this. And the study was only 500 people, all Americans.

How different the results might be in other countries and cultures is still an open question. Would populations whose attitudes are more strongly shaped by religion respond differently? Would the populations of countries that have been invaded and dominated by other countries be more nervous about alien life or habitable exoplanets? There’s only conjecture at this point.

Maybe we’re novelty-seekers and we thrive on new discoveries. Or maybe we’re truth-seekers, and that’s reflected in the study. Maybe some of the positivity reflects our fear of being alone. If Earth is the only life-supporting world, that’s a very lonely proposition. Not only that, but it’s an awesome responsibility: we better not screw it up!

Still, the results are encouraging for humanity. We seem, at least according to this first study, open to the discovery of alien life.

But that might change when the first alien ship casts its shadow over Los Angeles.

The Mars Project! Von Braun’s Ideas for a Mars Mission. Collaboration with Vintage Space

Humans to Mars!

Did you know that it’s been almost 45 years since humans walked on the surface of the Moon? Of course you do. Anyone who loves space exploration obsesses about the last Apollo landings, and counts the passing years of sadness.

Sure, SpaceX, Blue Origins and the new NASA Space Launch Systems rocket offer a tantalizing future in space. But 45 years. Ouch, so much lost time.

What would happen if we could go back in time? What amazing and insane plans did NASA have to continue exploring the Solar System? What alternative future could we have now, 45 years later?

In order to answer this question, I’ve teamed up with my space historian friend, Amy Shira Teitel, who runs the Vintage Space blog and YouTube Channel. We’ve decided to look at two groups of missions that never happened.

In her part, Amy talks about the Apollo Applications Program; NASA’s original plans before the human exploration of the Moon was shut down. More Apollo missions, the beginnings of a lunar base, and even a human flyby of Venus.

In my half of the series, I look at Werner Von Braun’s insanely ambitious plans to send a human mission to Mars. Put it together with Amy’s episode and you can imagine a space exploration future with all the ambition of the Kerbal Space Program.

Keep mind here that we’re not going to constrain ourselves with the pesky laws of physics, and the reality of finances. These ideas were cool, and considered by NASA engineers, but they weren’t necessarily the best ideas, or even feasible.

So, 2 parts, tackle them in any order you like. My part begins right now.

Werner Von Braun, of course, was the architect for NASA’s human spaceflight efforts during the space race. It was under Von Braun’s guidance that NASA developed the various flight hardware for the Mercury, Gemini and Apollo missions including the massive Saturn V rocket, which eventually put a human crew of astronauts on the Moon and safely returned them back to Earth.

Wernher von Braun. Credit: NASA/Marshall Space Flight Center

Von Braun was originally a German rocket scientist, pivotal to the Nazi “rocket team”, which developed the ballistic V-2 rockets. These unmanned rockets could carry a 1-tonne payload 800 kilometers away. They were developed in 1942, and by 1944 they were being used in war against Allied targets.

By the end of the war, Von Braun coordinated his surrender to the Allies as well as 500 of his engineers, including their equipment and plans for future rockets. In “Operation Paperclip”, the German scientists were captured and transferred to the White Sands Proving Ground in New Mexico, where they would begin working on the US rocket efforts.

Von Braun and others standing in front a V-2 rocket engine at White Sands. Credit: U.S. Army/ Ordway Collection/Space Rocket Center

Before the work really took off, though, Von Braun had a couple of years of relative downtime, and in 1947 and 1948, he wrote a science fiction novel about the human exploration of Mars.

The novel itself was never published, because it was terrible, but it also contained a detailed appendix containing all the calculations, mission parameters, hardware designs to carry out this mission to Mars.

The Mars Project

In 1952, this appendix was published in Germany as “Das Marsproject”, or “The Mars Project”. And an English version was published a few years later. Collier’s Weekly Magazine did an 8-part special on the Mars Project in 1952, captivating the world’s imagination.

Here’s the plan: In the Mars Project, Von Braun envisioned a vast armada of spaceships that would make the journey from Earth to Mars. They would send a total of 10 giant spaceships, each of which would weigh about 4,000 tonnes.

Just for comparison, a fully loaded Saturn V rocket could carry about 140 tonnes of payload into Low Earth Orbit. In other words, they’d need a LOT of rockets. Von Braun estimated that 950 three-stage rockets should be enough to get everything into orbit.

Ships being assembled in orbit. Credit: Collier’s

All the ships would be assembled in orbit, and 70 crewmembers would take to their stations for an epic journey. They’d blast their rockets and carry out a Mars Hohmann transfer, which would take them 8 months to make the journey from Earth to Mars.

The flotilla consisted of 7 orbiters, huge spheres that would travel to Mars, go into orbit and then return back to Earth. It also consisted of 3 glider landers, which would enter the Martian atmosphere and stay on Mars.

Once they reached the Red Planet, they would use powerful telescopes to scan the Martian landscape and search for safe and scientifically interesting landing spots. The first landing would happen at one of the planet’s polar caps, which Von Braun figured was the only guaranteed flat surface for a landing.

A rocket-powered glider descending towards Mars. Credit: Collier’s

At this point, it’s important to note that Von Braun assumed that the Martian atmosphere was about as thick as Earth’s. He figured you could use huge winged gliders to aerobrake into the atmosphere and land safely on the surface.

He was wrong. The atmosphere on Mars is actually only 1% as thick as Earth’s, and these gliders would never work. Newer missions, like SpaceX’s Red Dragon and Interplanetary Transport Ship will use rockets to make a powered landing.

I think if Von Braun knew this, he could have modified his plans to still make the whole thing work.

Landed at the polar cap. Credit: Collier’s

Once the first expedition landed at one of the polar caps, they’d make a 6,400 kilometer journey across the harsh Martian landscape to the first base camp location, and build a landing strip. Then two more gliders would detach from the flotilla and bring the majority of the explorers to the base camp. A skeleton crew would remain in orbit.

Once again, I think it’s important to note that Von Braun didn’t truly understand how awful the surface of Mars really is. The almost non-existent atmosphere and extreme cold would require much more sophisticated gear than he had planned for. But still, you’ve got to admire his ambition.

Preparing the gliders for rocket-powered ascent. Credit: Collier’s

With the Mars explorer team on the ground, their first task was to turn their glider-landers into rockets again. They would stand them up and get them prepped to blast off from the surface of Mars when their mission was over.

The Martian explorers would set up an inflatable habitat, and then spend the next 400 days surveying the area. Geologists would investigate the landscape, studying the composition of the rocks. Botanists would study the hardy Martian plant life, and seeing what kinds of Earth plants would grow.

Zoologists would study the local animals, and help figure out what was dangerous and what was safe to eat. Archeologists would search the region for evidence of ancient Martian civilizations, and study the vast canal network seen from Earth by astronomers. Perhaps they’d even meet the hardy Martians that built those canals, struggling to survive to this day.

Once again, in the 1940s, we thought Mars would be like the Earth, just more of a desert. There’d be plants and animals, and maybe even people adapted to the hardy environment. With our modern knowledge, this sounds quaint today. The most brutal desert on Earth is a paradise compared to the nicest place on Mars. Von Braun did the best he could with the best science of the time.

Finally, at the end of their 400 days on Mars, the astronauts would blast off from the surface of Mars, meet up with the orbiting crew, and the entire flotilla would make the return journey to Earth using the minimum-fuel Mars-Earth transfer trajectory.

The planned trajectories to and from Mars. Credit: Collier’s

Although Von Braun got a lot of things wrong about his Martian mission plan, such as the thickness of the atmosphere and habitability of Mars, he got a lot of things right.

He anticipated a mission plan that required the least amount of fuel, by assembling pieces in orbit, using the Hohmann transfer trajectory, exploring Mars for 400 days to match up Earth and Mars orbits. He developed the concept of using orbiters, detachable landing craft and ascent vehicles, used by the Apollo Moon missions.

The missions never happened, obviously, but Von Braun’s ideas served as the backbone for all future human Mars mission plans.

I’d like to give a massive thanks to the space historian David S.F. Portree. He wrote an amazing book called Humans to Mars, which details 50 years of NASA plans to send humans to the Red Planet, including a fantastic synopsis of the Mars Project.

I asked David about how Von Braun’s ideas influenced human spaceflight, he said it was his…

“… reliance on a conjunction-class long-stay mission lasting 400 days. That was gutsy – in the 1960s, NASA and contractor planners generally stuck with opposition-class short-stay missions. In recent years we’ve seen more emphasis on the conjunction-class mission mode, sometimes with a relatively short period on Mars but lots of time in orbit, other times with almost the whole mission spent on the surface.”

Do Stars Move? Tracking Their Movements Across the Sky

How Fast Are Stars Moving?


The night sky, is the night sky, is the night sky. The constellations you learned as a child are the same constellations that you see today. Ancient people recognized these same constellations. Oh sure, they might not have had the same name for it, but essentially, we see what they saw.

But when you see animations of galaxies, especially as they come together and collide, you see the stars buzzing around like angry bees. We know that the stars can have motions, and yet, we don’t see them moving?

How fast are they moving, and will we ever be able to tell?

Stars, of course, do move. It’s just that the distances are so great that it’s very difficult to tell. But astronomers have been studying their position for thousands of years. Tracking the position and movements of the stars is known as astrometry.

We trace the history of astrometry back to 190 BC, when the ancient Greek astronomer Hipparchus first created a catalog of the 850 brightest stars in the sky and their position. His student Ptolemy followed up with his own observations of the night sky, creating his important document: the Almagest.

Printed rendition of a geocentric cosmological model from Cosmographia, Antwerp, 1539. Credit: Wikipedia Commons/Fastfission

In the Almagest, Ptolemy laid out his theory for an Earth-centric Universe, with the Moon, Sun, planets and stars in concentric crystal spheres that rotated around the planet. He was wrong about the Universe, of course, but his charts and tables were incredibly accurate, measuring the brightness and location of more than 1,000 stars.

A thousand years later, the Arabic astronomer Abd al-Rahman al-Sufi completed an even more detailed measurement of the sky using an astrolabe.

One of the most famous astronomers in history was the Danish Tycho Brahe. He was renowned for his ability to measure the position of stars, and built incredibly precise instruments for the time to do the job. He measured the positions of stars to within 15 to 35 arcseconds of accuracy. Just for comparison, a human hair, held 10 meters away is an arcsecond wide.

Also, I’m required to inform you that Brahe had a fake nose. He lost his in a duel, but had a brass replacement made.

In 1807, Friedrich Bessel was the first astronomer to measure the distance to a nearby star 61 Cygni. He used the technique of parallax, by measuring the angle to the star when the Earth was on one side of the Sun, and then measuring it again 6 months later when the Earth was on the other side.

With parallax technique, astronomers observe object at opposite ends of Earth’s orbit around the Sun to precisely measure its distance. Credit: Alexandra Angelich, NRAO/AUI/NSF.

Over the course of this period, this relatively closer star moves slightly back and forth against the more distant background of the galaxy.

And over the next two centuries, other astronomers further refined this technique, getting better and better at figuring out the distance and motions of stars.

But to really track the positions and motions of stars, we needed to go to space. In 1989, the European Space Agency launched their Hipparcos mission, named after the Greek astronomer we talked about earlier. Its job was to measure the position and motion of the nearby stars in the Milky Way. Over the course of its mission, Hipparcos accurately measured 118,000 stars, and provided rough calculations for another 2 million stars.

That was useful, and astronomers have relied on it ever since, but something better has arrived, and its name is Gaia.

Credit: ESA/ATG medialab; Background Credit: ESO/S. Brunier

Launched in December 2013, the European Space Agency’s Gaia in is in the process of mapping out a billion stars in the Milky Way. That’s billion, with a B, and accounts for about 1% of the stars in the galaxy. The spacecraft will track the motion of 150 million stars, telling us where everything is going over time. It will be a mind bending accomplishment. Hipparchus would be proud.

With the most precise measurements, taken year after year, the motions of the stars can indeed be calculated. Although they’re not enough to see with the unaided eye, over thousands and tens of thousands of years, the positions of the stars change dramatically in the sky.

The familiar stars in the Big Dipper, for example, look how they do today. But if you go forward or backward in time, the positions of the stars look very different, and eventually completely unrecognizable.

When a star is moving sideways across the sky, astronomers call this “proper motion”. The speed a star moves is typically about 0.1 arc second per year. This is almost imperceptible, but over the course of 2000 years, for example, a typical star would have moved across the sky by about half a degree, or the width of the Moon in the sky.

A 20 year animation showing the proper motion of Barnard’s Star. Credit: Steve Quirk, images in the Public Domain.

The star with the fastest proper motion that we know of is Barnard’s star, zipping through the sky at 10.25 arcseconds a year. In that same 2000 year period, it would have moved 5.5 degrees, or about 11 times the width of your hand. Very fast.

When a star is moving toward or away from us, astronomers call that radial velocity. They measure this by calculating the doppler shift. The light from stars moving towards us is shifted towards the blue side of the spectrum, while stars moving away from us are red-shifted.

Between the proper motion and redshift, you can get a precise calculation for the exact path a star is moving in the sky.

Credit: ESA/ATG medialab

We know, for example, that the dwarf star Hipparcos 85605 is moving rapidly towards us. It’s 16 light-years away right now, but in the next few hundred thousand years, it’s going to get as close as .13 light-years away, or about 8,200 times the distance from the Earth to the Sun. This won’t cause us any direct effect, but the gravitational interaction from the star could kick a bunch of comets out of the Oort cloud and send them down towards the inner Solar System.

The motions of the stars is fairly gentle, jostling through gravitational interactions as they orbit around the center of the Milky Way. But there are other, more catastrophic events that can make stars move much more quickly through space.

When a binary pair of stars gets too close to the supermassive black hole at the center of the Milky Way, one can be consumed by the black hole. The other now has the velocity, without the added mass of its companion. This gives it a high-velocity kick. About once every 100,000 years, a star is kicked right out of the Milky Way from the galactic center.

A rogue star being kicked out of a galaxy. Credit: NASA, ESA, and G. Bacon (STScI)

Another situation can happen where a smaller star is orbiting around a supermassive companion. Over time, the massive star bloats up as supergiant and then detonates as a supernova. Like a stone released from a sling, the smaller star is no longer held in place by gravity, and it hurtles out into space at incredible speeds.

Astronomers have detected these hypervelocity stars moving at 1.1 million kilometers per hour relative to the center of the Milky Way.

All of the methods of stellar motion that I talked about so far are natural. But can you imagine a future civilization that becomes so powerful it could move the stars themselves?

In 1987, the Russian astrophysicist Leonid Shkadov presented a technique that could move a star over vast lengths of time. By building a huge mirror and positioning it on one side of a star, the star itself could act like a thruster.

An example of a stellar engine using a mirror and a Dyson Swarm. Credit: Vedexent at English Wikipedia (CC BY-SA 3.0)

Photons from the star would reflect off the mirror, imparting momentum like a solar sail. The mirror itself would be massive enough that its gravity would attract the star, but the light pressure from the star would keep it from falling in. This would create a slow but steady pressure on the other side of the star, accelerating it in whatever direction the civilization wanted.

Over the course of a few billion years, a star could be relocated pretty much anywhere a civilization wanted within its host galaxy.

This would be a true Type III Civilization. A vast empire with such power and capability that they can rearrange the stars in their entire galaxy into a configuration that they find more useful. Maybe they arrange all the stars into a vast sphere, or some kind of geometric object, to minimize transit and communication times. Or maybe it makes more sense to push them all into a clean flat disk.

Amazingly, astronomers have actually gone looking for galaxies like this. In theory, a galaxy under control by a Type III Civilization should be obvious by the wavelength of light they give off. But so far, none have turned up. It’s all normal, natural galaxies as far as we can see in all directions.

For our short lifetimes, it appears as if the sky is frozen. The stars remain in their exact positions forever, but if you could speed up time, you’d see that everything is in motion, all the time, with stars moving back and forth, like airplanes across the sky. You just need to be patient to see it.

Now, Witness The Power Of This Fully Operational Radio Telescope!

Relax, its not a space station! And according to the Chinese government, it’s for entirely peaceful purposes. It’s known as the Five-hundred-meter Aperture Spherical Telescope (FAST), a massive array that just finished construction in the southerwestern province of Guizhou, China. Equivalent in size to over 20 football fields joined end to end, it is the world’s largest radio telescope – thus ending the Arecibo Observatory’s 53 year reign.

As part of China’s growing commitment to space exploration, the FAST telescope will spend the coming decades exploring space and assisting in the hunt for extraterrestrial life. And once it commences operations this coming September, the Chinese expect it will remain the global leader in radio astronomy for the next ten or twenty years.

In addition to being larger than the Arecibo Observatory (which measures 305 meters in diameter), the telescope is reportedly 10 times more sensitive than its closest competitor – the steerable 100-meter telescope near Bonn, Germany. What’s more, unlike Arecibo (which has a fixed spherical curvature), FAST is capable of forming a parabolic mirror. That will allow researchers a greater degree of flexibility.

The Chinese Academy of Sciences (CAS) has spent the past five years building the telesccope, to the tune of 1.2-billion-yuan (180 million U.S. dollars). As the deputy head of the National Astronomical Observation, which is overseen by the CAS, Zheng Xiaonian was present at the celebrations marking the completion of the massive telescope.

As he was paraphrased as saying by the Xinhua News Agency: “The project has the potential to search for more strange objects to better understand the origin of the universe and boost the global hunt for extraterrestrial life.” Zheng was also quoted as saying that he expects FAST to be the global leader in radio astronomy for the next 10 to 20 years.

The construction of this array has also been a source of controversy. To protect the telescope from radio interference, Chinese authorities built FAST in Guizhou province’s isolated Dawodang depression, directly into the mountainside. However, to ensure that no magnetic disruptions are nearby, roughly 9,000 people are being removed from their homes and rehoused in the neighboring counties of Pingtang and Luodian.

FAST_overheadLi Yuecheng is the secretary-general of the Guizhou Provincial Committee, which is part of the Chinese People’s Political Consultative Conference (CPPCC). As he was quoted as saying by the Xinhua News Agency, the move comes with compensation:

“The proposal asked the government to relocate residents within 5 kilometers of the Five-hundred-meter Aperture Spherical Telescope, or FAST, to create a sound electromagnetic wave environment… Each of the involved residents will get 12,000 yuan (1,838 U.S. dollars) subsidy from the provincial reservoir and eco-migration bureau, and each involved ethnic minority household with housing difficulties will get 10,000 yuan subsidy from the provincial ethnic and religious committee.”

Mosaic of the Chang'e-3 moon lander and the lunar surface taken by the camera on China’s Yutu moon rover from a position south of the lander during Lunar Day 3. Note the landing ramp and rover tracks at left. Credit: CNSA/SASTIND/Xinhua/Marco Di Lorenzo/Ken Kremer
China’s recent forays into space include the Chang’e-3 moon lander, seen here by the Yutu moon rover. Credit: CNSA/SASTIND/Xinhua/Marco Di Lorenzo/Ken Kremer

In addition, the construction of this telescope is seen by some as part of a growing desire on behalf of China to press its interests in the geopolitical realm. For instance, in their 2016 Annual Report to Congress, the Department of Defense indicated that China is looking to develop its space capabilities to prevent adversaries from being able to use space-based assets in a crisis. As the report states:

“In parallel with its space program, China continues to develop a variety of counterspace capabilities designed to limit or to prevent the use of space-based assets by the [Peoples’ Liberation Army’s] adversaries during a crisis or conflict… Although China continues to advocate the peaceful use of outer space, the report also noted China would ‘secure its space assets to serve its national economic and social development, and maintain outer space security.'”

However, for others, FAST is merely the latest step in China’s effort to become a superpower in the all-important domain of space exploration and research. Their other ambitions include mounting a crewed mission to the Moon by 2036 and building a space station (for which work has already begun). In addition, FAST will enable China to take part in another major area of space research, which is the search for extra-terrestrial life.

For decades, countries like the United States have leading this search through efforts like the SETI Institute and the Nexus for Exoplanet System Science (NExSS). But with the completion of this array, China now has the opportunity to make significant contributions in the hunt for alien intelligence.

In the meantime, the CAS’ scientists will be debugging the telescope and conducting trials in preparation for its activation, come September. Once it is operational, it will assist in other areas of research as well, which will include conducting surveys of neutral hydrogen in the Milky Way and other galaxies, as well as detecting pulsars and gravitational waves.

Further Reading: Xinhuanet

Is There a Kraken in Kraken Mare? What Kind of Life Would We Find on Titan?

The left image shows a mosaic of images of Titan taken by the Cassini spacecraft in near infrared light. Titan’s polar seas are visible as sunlight glints off of them. The right image is a radar image of Kraken Mare. Credit: NASA Jet Propulsion Laboratory.

Could there be life on Saturn’s large moon Titan? Asking the question forces astrobiologists and chemists to think carefully and creatively about the chemistry of life, and how it might be different on other worlds than it is on Earth. In February, a team of researchers from Cornell University, including chemical engineering graduate student James Stevenson, planetary scientist Jonathan Lunine, and chemical engineer Paulette Clancy, published a pioneering study arguing that cell membranes could form under the exotic chemical conditions present on this remarkable moon.

In many ways, Titan is Earth’s twin. It’s the second largest moon in the solar system and bigger than the planet Mercury. Like Earth, it has a substantial atmosphere, with a surface atmospheric pressure a bit higher than Earth’s. Besides Earth, Titan is the only object in our solar system known to have accumulations of liquid on its surface. NASA’s Cassini space probe discovered abundant lakes and even rivers in Titan’s polar regions. The largest lake, or sea, called Kraken Mare, is larger than Earth’s Caspian Sea. Researchers know from both spacecraft observations and laboratory experiments that Titan’s atmosphere is rich in complex organic molecules, which are the building blocks of life.

All these features might make it seem as though Titan is tantalizingly suitable for life. The name ‘Kraken’, which refers to a legendary sea monster, fancifully reflects the eager hopes of astrobiologists. But, Titan is Earth’s alien twin. Being almost ten times further from the sun than Earth is, its surface temperature is a frigid -180 degrees Celsius. Liquid water is vital to life as we know it, but on Titan’s surface all water is frozen solid. Water ice takes on the role that silicon-containing rock does on Earth, making up the outer layers of the crust.

The liquid that fills Titan’s lakes and rivers is not water, but liquid methane, probably mixed with other substances like liquid ethane, all of which are gases here on Earth. If there is life in Titan’s seas, it is not life as we know it. It must be an alien form of life, with organic molecules dissolved in liquid methane instead of liquid water. Is such a thing even possible?

The Cornell team took up one key part of this challenging question by investigating whether cell membranes can exist in liquid methane. Every living cell is, essentially, a self-sustaining network of chemical reactions, contained within bounding membranes. Scientists think that cell membranes emerged very early in the history of life on Earth, and their formation might even have been the first step in the origin of life.

Here on Earth, cell membranes are as familiar as high school biology class. They are made of large molecules called phospholipids. Each phospholipid molecule has a ‘head’ and a ‘tail’. The head contains a phosphate group, with a phosphorus atom linked to several oxygen atoms. The tail consists of one or more strings of carbon atoms, typically 15 to 20 atoms long, with hydrogen atoms linked on each side. The head, due to the negative charge of its phosphate group, has an unequal distribution of electrical charge, and we say that it is polar. The tail, on the other hand, is electrically neutral.

phospholipid membrane
Here on Earth, cell membranes are composed of phospholipid molecules dissolved in liquid water. A phospholipid has a backbone of carbon atoms (gray), and also contains hydrogen (sky blue), phosphorus (yellow), oxygen (red), and nitrogen (blue). Due to the positive charge associated with the nitrogen containing choline group, and the negative charge associated with the phosphate group, the head is polar, and attracts water. It is therefore hydrophilic. The hydrocarbon tail is electrically neutral and hydrophobic. The structure of a cell membrane is due these electrical properties of phospholipids and water. The molecules form a double layer, with the hydrophilic heads facing outward, towards water, and the hydrophobic tails facing inward, towards one another. Credit: Ties van Brussel

These electrical properties determine how phospholipid molecules will behave when they are dissolved in water. Electrically speaking, water is a polar molecule. The electrons in the water molecule are more strongly attracted to its oxygen atom than to its two hydrogen atoms. So, the side of the molecule where the two hydrogen atoms are has a slight positive charge, and the oxygen side has a small negative charge. These polar properties of water cause it to attract the polar head of the phospholipid molecule, which is said to be hydrophilic, and repel its nonpolar tail, which is said to be hydrophobic.

When phospholipid molecules are dissolved in water, the electrical properties of the two substances work together to cause the phospholipid molecules to organize themselves into a membrane. The membrane closes onto itself into a little sphere called a liposome. The phospholipid molecules form a bilayer two molecules thick. The polar hydrophilic heads face outward towards the water on both the inner and outer surface of the membrane. The hydrophobic tails are sandwiched between, facing each other. While the phospholipid molecules remain fixed in their layer, with their heads facing out and their tails facing in, they can still move around with respect to each other, giving the membrane the fluid flexibility needed for life.

Phospholipid bilayer membranes are the basis of all terrestrial cell membranes. Even on its own, a liposome can grow, reproduce and aid certain chemical reactions important to life, which is why some biochemists think that the formation of liposomes might have been the first step towards life. At any rate, the formation of cell membranes must surely been an early step in life’s emergence on Earth.

water and methane
At the left, water, consisting of hydrogen (H) and oxygen (O), is a polar solvent. Oxygen attracts electrons more strongly than hydrogen does, giving the hydrogen side of the molecule a net positive charge and the oxygen side a net negative charge. The delta symbol ( ) indicates that the charge is partial, that is less than a full unit of positive or negative charge. At right, methane is a non-polar solvent, due to the symmetrical distribution of hydrogen atoms (H) around a central carbon atom (C). Credit: Jynto as modified by Paul Patton.

If some form of life exists on Titan, whether sea monster or (more likely) microbe, it would almost certainly need to have a cell membrane, just like every living thing on Earth does. Could phospholipid bilayer membranes form in liquid methane on Titan? The answer is no. Unlike water, the methane molecule has an even distribution of electrical charges. It lacks water’s polar qualities, and so couldn’t attract the polar heads of phospholipid molecule. This attraction is needed for the phospholipids to form an Earth-style cell membrane.

Experiments have been conducted where phospholipids are dissolved in non-polar liquids at Earthly room temperature. Under these conditions, the phospholipids form an ‘inside-out’ two layer membrane. The polar heads of the phospholipid molecules are at the center, attracted to one another by their electrical charges. The non-polar tails face outward on each side of the inside-out membrane, facing the non-polar solvent.

membranes in polar and non-polar solvents
At left, phospholipids are dissolved in water, a polar solvent. They form a bilayer membrane, with their polar, hydrophilic heads facing outward towards water, and their hydrophobic tails facing each other. At right, when phospholipids are dissolved in a non-polar solvent at Earthly room temperature, they form an inside-out membrane, with the polar heads attracting one another, and the non-polar tails facing outwards towards the non-polar solvent. Based on figure 2 from Stevenson, Lunine, and Clancy (2015). Credit: Paul Patton

Could Titanian life have an inside out phospholipid membrane? The Cornell team concluded that this wouldn’t work, for two reasons. The first is that at the cryogenic temperatures of liquid methane, the tails of phospholipids become rigid, depriving any inside-out membrane that might form of the fluid flexibility needed for life. The second is that two key ingredients of phospholipids; phosphorus and oxygen, are probably unavailable in the methane lakes of Titan. In their search for Titanian cell membranes, the Cornell team needed to probe beyond the familiar realm of high school biology.

Although not composed of phospholipids, the scientists reasoned that any Titanian cell membrane would nevertheless be like the inside-out phospholipid membranes created in the lab. It would consist of polar molecules clinging together electrically in a solution of non-polar liquid methane. What molecules might those be? For answers the researchers looked to data from the Cassini spacecraft and from laboratory experiments that reproduced the chemistry of Titan’s atmosphere.

Titan’s atmosphere is known to have a very complex chemistry. It is made mostly of nitrogen and methane gas. When the Cassini spacecraft analyzed its composition using spectroscopy it found traces of a variety of compounds of carbon, nitrogen, and hydrogen, called nitriles and amines. Researchers have simulated the chemistry of Titan’s atmosphere in the lab by exposing mixtures of nitrogen and methane to sources of energy simulating sunlight on Titan. A stew of organic molecules called ‘tholins’ is formed. It consists of compounds of hydrogen and carbon, called hydrocarbons, as well as nitriles and amines.

The Cornell investigators saw nitriles and amines as potential candidates for their Titanian cell membranes. Both are polar molecules that might stick together to form a membrane in non-polar liquid methane due to the polarity of nitrogen containing groups found in both of them. They reasoned that candidate molecules must be much smaller than phospholipids, so that they could form fluid membranes at liquid methane temperatures. They considered nitriles and amines containing strings of between three and six carbon atoms. Nitrogen containing groups are called ‘azoto’ –groups, so the team named their hypothetical Titanian counterpart to the liposome the ‘azotosome’.

Synthesizing azotosomes for experimental study would have been difficult and expensive, because the experiments would need to be conducted at the cryogenic temperatures of liquid methane. But since the candidate molecules have been studied extensively for other reasons, the Cornell researchers felt justified in turning to the tools of computational chemistry to determine whether their candidate molecules could cohere as a flexible membrane in liquid methane. Computational models have been used successfully to study conventional phospholipid cell membranes.

acrylonitrile
Acrylonitrile has been identified as a possible basis for cell membranes in liquid methane on Titan. It is known to be present in Titan’s atmosphere at a concentration of 10 parts per million and has been produced in laboratory simulations of the effects of energy sources on Titan’s nitrogen-methane atmosphere. As a small polar molecule capable of dissolving in liquid methane, it is a candidate substance for the formation of cell membranes in an alternative biochemistry on Titan. Light blue: carbon atoms, dark blue: nitrogen atom, white: hydrogen atoms. Credit: Ben Mills as modified by Paul Patton.

acrylonitrile membrane
Polar acrylonitrile molecules align ‘head’ to ‘tail’ to form a membrane in non-polar liquid methane. Light blue: carbon atoms, dark blue: nitrogen atoms, white: hydrogen atoms. Credit: James Stevenson.

The group’s computational simulations showed that some candidate substances could be ruled out because they would not cohere as a membrane, would be too rigid, or would form a solid. Nevertheless, the simulations also showed that a number of substances would form membranes with suitable properties. One suitable substance is acrylonitrile, which Cassini showed is present in Titan’s atmosphere at 10 parts per million concentration. Despite the huge difference in temperature between cryogenic azotozomes and room temperature liposomes, the simulations showed them to exhibit strikingly similar properties of stability and response to mechanical stress. Cell membranes, then, are possible for life in liquid methane.

azotosome
Computational chemistry simulations show that acrylonitrile and some other small polar nitrogen containing organic molecules are capable of forming ‘azotosomes’ when they are dissolved on liquid methane. Azotosomes are small membrane bounded spherules like the liposomes formed by phospholipids when they are dissolved in water. The simulations show that acrylonitrile azotosomes would be both stable and flexible in cryogenically cold liquid methane, giving them the properties they need to function as cell membranes for hypothetical Titanian life, or for life on any world with liquid methane on its surface. The azotosome shown is 9 nanometers in size, about the size of a virus. Light blue: carbon atoms, dark blue: nitrogen atoms, white: hydrogen atoms. Credit: James Stevenson.

The scientists from Cornell view their findings as nothing more than a first step towards showing that life in liquid methane is possible, and towards developing the methods that future spacecraft will need to search for it on Titan. If life is possible in liquid methane, the implications ultimately extend far beyond Titan.

When seeking conditions suitable for life in the galaxy, astronomers typically search for exoplanets within a star’s habitable zone, defined as the narrow range of distances over which a planet with an Earth-like atmosphere would have a surface temperature suitable for liquid water. If methane life is possible, then stars would also have a methane habitable zone, a region where methane could exist as a liquid on a planet or moon, making methane life possible. The number of habitable worlds in the galaxy would be greatly increased. Perhaps, on some worlds, methane life evolves into complex forms that we can scarcely imagine. Maybe some of them are even a bit like sea monsters.

References and Further Reading:

N. Atkinson (2010) Alien Life on Titan? Hang on Just a Minute, Universe Today.

N. Atkinson (2010) Life on Titan Could be Smelly and Explosive, Universe Today.

M. L. Cable, S. M. Horst, R. Hodyss, P. M. Beauchamp, M. A. Smith, P. A. Willis, (2012) Titan tholins: Simulating Titan organic chemistry in the Cassini-Huygens era, Chemical Reviews, 112:1882-1909.

E. Howell (2014) Titan’s Majestic Mirror-Like Lakes Will Come Under Cassini’s Scrutiny This Week, Universe Today.

J. Major (2013) Titan’s North Pole is Loaded With Lakes, Universe Today.

C. P. McKay, H. D. Smith, (2005) Possibilities for methanogenic life in liquid methane on the surface of Titan, Icarus 178: 274-276.

J. Stevenson, J. Lunine, P. Clancy, (2015) Membrane alternatives in worlds without oxygen: Creation of an azotosome, Science Advances 1(1):e1400067.

S. Oleson (2014) Titan submarine: Exploring the depths of Kraken, NASA Glenn Research Center, Press release.

Cassini Solstice Mission, NASA Jet Propulsion Laboratory

NASA and ESA celebrate 10 years since Titan landing, NASA 2015

What are the Galilean Moons?

It’s no accident that Jupiter shares its name with the king of the gods. In addition to being the largest planet in our Solar System – with two and a half times the mass of all the other planets combined – it is also home to some of the largest moons of any Solar planet. Jupiter’s largest moons are known as the Galileans, all of which were discovered by Galileo Galilei and named in his honor.

They include Io, Europa, Ganymede, and Callisto, and are the Solar System’s fourth, sixth, first and third largest satellites, respectively. Together, they contain almost 99.999% of the total mass in orbit around Jupiter, and range from being 400,000 and 2,000,000 km from the planet. Outside of the Sun and eight planets, they are also among the most massive objects in the Solar System, with radii larger than any of the dwarf planets.

Continue reading “What are the Galilean Moons?”