Archives For astronomy

europa

We’ve long known that there was an ocean or something very much like it under the icy crust of the Jovian moon Europa, and that this icy wasteland offers one of the best chances to find life in our solar system despite living in a very turbulent and radioactive neighborhood. And now, the same astronomer who stunned Pluto before the IAU’s planetary double-tap, Mike Brown, found strong evidence that Europa’s ocean is leaking to the surface and is salty like ours. Basically, a short summary of the elegant details I encourage you to read from Dr. Brown himself is that the chemical residues on the moon’s surface match up with exactly what we’d expect if it had a thick, salty, liquid ocean which periodically rises through the cracks in the ice and leaves deposits as it recedes with the tides. We could learn even more, but radiation scatters other compounds we could measure from our post right here on the blue marble. So far, though, so good for bacteria and multicellular colonies that could potentially call Europa home.

Now it’s very important to know that organic chemical signatures do not always mean life and a distinct lack of experience with alien organisms on our part means that until we actually see one with our probes and run several hundred tests and a few thousand reviews of the data from all those tests, we won’t know if we found alien organisms. Well, unless an alien fish just wiggles to the camera and waves hello. That would speed up the announcement. But in all seriousness, as far as cases for promising habitats go, everything we find about Europa makes it look better and better for exploration. The only problem is that the ocean where so much life could exist lies so far down, in some cases under several miles of ice. Drilling through it is complicated and really dangerous for robotic probes, so the focus has been on trying to get access to the ocean with a minimum of digging, using something like a rover with a tiny submarine to explore the shallows. If what Brown has found is any indication, we might find even more about Europa’s chemistry this way since some of the more scientifically interesting chemicals could just float up to us.

However, keep in mind that the moon’s surface is bathed by radiation and microorganisms that evolve under several miles of ice and meters of water would be instantly fried to a crisp if they’re exposed to it, leaving promising but ambiguous residue on the surface. For anything more alien and complex than extremophiles that may have even survived the trip from Earth, we will need to be ready to dive deep and look far and wide. It’s actually another reason for human exploration of the outer solar system. Robots can only be made so clever in space, and they’re not good at dealing with the unknown and the uncertain, having no instinct or useful previous experiences from which to make decisions about new environments. Having humans guide them as they look for alien life on an unknown, largely unfamiliar world would be a terrific fusion of our brainpower and machine endurance that could lead to something as big as proof that we’re not alone. That knowledge alone should justify the effort of making the trip.

[ illustration by Guillermo Krieger ]

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insignificance

Since the dawn of modern cosmology there’s been an implicit assumption that no particular spot in the universe was supposed to be any more special than the rest. On the biggest scales of all, scales at which galaxies are treated like tiny particles, the universe is supposed to be isotropic and homogeneous i.e. more or less uniform in composition and its expansion from the Big Bang. For decades, simulations and observations seemed to show that this was really the case, but as a newly published paper argues, this might no longer be the true because lurking at the dawn of the universe was a group of quasars stretching for nearly 4 billion light years and tipping the very large metaphorical scales at 6.1 quintillion solar masses. That’s a big enough cluster to shatter the theorized limit on how big cosmological structures should be able to get by a factor of four. It looks as if the cosmological principle might need some refining unless it turns out that data from the Sloan Digital Sky survey is wrong and this cluster is much, much smaller than it appears.

Here are the basics on the fancifully named Huge Large Quasar Group, or Huge-LQG for short. It’s made up of 73 quasars arranged like a Y chromosome that was been shot right through the center with a high speed projectile. The upper, crescent-shaped branch is 56 quasars and the remaining 17 cluster tightly right underneath it. It’s about eight times the width of the Great Wall, which was once considered such an enormous cluster of galaxies that it too was once billed as a discovery that would challenge the cosmological constant. But simulations showed that it simply wasn’t big enough and that clusters as wide as 1.2 billion light years still leave the cosmos more or less uniform and isotropic. And this is the major issue with Huge-LQG. It’s almost four times wider and there’s no explanation for how a structure this big could exist without being torn apart by gravity and the expansion of space-time long before it gets anywhere near that size. Now, we can’t exactly toss the cosmological principle away yet, but we at least have to refine it.

Obviously, something is missing and if we were to simply adjust and say that 4 billion light years should now be the new limit on quasar groups, we would be missing why that’s the case. Letting go of the cosmological principle opens us to new models of galactic and cosmic evolution and exciting new ideas. However, it’s not really that simple because we’d also have to explain how an anisotropic early universe became the mostly isotropic, homogeneous mature one we see today while working in the confined space of a finite cosmos. One easy way to stick with homogeneity could be to declare that the known universe must be much bigger than we think because if your scale is big enough, anything can become small enough to be homogenized into your structure, but without being able to see beyond 13 billion light years or so, super-sizing the universe is an extremely questionable proposition. Either way, Huge-LQG leaves us with a dilemma that really gives the status quo a run for its money, and that’s how the really exciting breakthroughs can be made, fascinating new science gets done, and Nobel Prizes are eventually earned…

See: Clowes, R., et al. (2013). A structure in the early Universe at that exceeds the homogeneity scale of the R-W concordance cosmology MNRAS DOI: 10.1093/mnras/sts497

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pandora

Another day, another study identifying more potentially habitable worlds in the Kepler data, this time by professional astronomers and volunteers called the Planet Hunters who discussed their planet detections on a specialized message board system called Talk. What they found was that more gas giants orbited stars in their habitable zones than initially thought, giving real evidence for the hypothesis that while alien Earths could be somewhat rare, moons orbiting alien Jupiters and Saturns may be a fairly common habitat for extraterrestrial life. Trouble is that we can’t see these moons or detect the wobble of the planets they orbit, so we don’t know how many of them there are, how big they are on average, and their likely composition. However, we do have very good reasons to assume that they could be there since gas giants in our own solar system are swarmed by moons of all shapes and sizes, and some are very possible hosts to life.

So one would think that a moon big enough to hold on to an atmosphere that’s not too dense or composed mainly of greenhouse gases in an alien star’s habitable zone would have liquid water in significant quantities. Even better, it would feel the gravitational tides of a gas giant that would in effect knead its interior, promoting volcanism, circulating rich organic matter that could either kick start living things or fuel them. Think of Io but more subdued and covered with oceans and small continents, or Titan without the mind-numbing cold. It could be a perfect habitat, and given billions of years, maybe even evolve intelligent life. But there’s a potential problem here. Typical solar system formation models dictate that rocky worlds form closer to a star than gas giants, so to be in the habitable zone of the vast majority of stars out there, alien Jupiters had to drift into these orbits, pushing out rocky worlds and reshuffling their siblings. What would that do to their moons? Would they be collateral damage in the upheaval of the solar system?

Ideally, the immense gravity of these gas giants would push planets aside as they spiral into the habitable zone and their clutches of icy rocks would slowly thaw to host oceans and fertile land for life to start taking hold. But again, the only way we’ll know this is if we build bigger and more powerful telescopes to detect their presence and hopefully one day resolve them as pixels for a quick spectrographic sniff of their atmospheres. Maybe, just maybe, decades from now, a future astronomer and a crew of enthusiastic volunteers will be looking through a data set collected by the latest planet hunting telescope and find a little bluish pixel next to a gas giant, or readings of a gas pointing to a stable biosphere, like oxygen from a recently discovered alien moon. It won’t be Earth 2.0, but it will be just as important, and we’ll be able to look up at the night sky knowing that we’re not alone because somewhere, a weird world with a killer view of a turbulent gas giant is home to something that can look back at Earth, even if it won’t wonder about us…

See: Wang, J., et al. (2013). Planet Hunters. V. A Confirmed Jupiter-Size Planet in the Habitable Zone and 42 Planet Candidates from the Kepler Archive Data arXiv: 1301.0644v1

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primordial black hole

Usually a new discovery in deep space tends to further complicate our picture of the universe, almost as if the cosmos says "oh yeah, you think you have a good idea of how this works?" and throws a monkey wrench into the works, or sometimes, the whole screaming, angry monkey. So when it comes to phenomena as complex and exciting as black holes, surely there can’t be any data that makes them easier to understand. But this time, when physicists wanted to figure out if jets from black holes followed the same patterns as the mass of the objects went up, nature was willing to cooperate. As it turns out, the powerful jets of material shot from the accretion disks of black holes of 20 solar masses and 20 million solar masses follow the same mechanism. How do we know that? By plotting their strength against the mass of the black hole. If the data follows a linear trend, we know that the physics don’t require a new process to explain the numbers.

So what exactly is happening around black holes? As you may already know, black holes aren’t the cosmic vacuum cleaners far too many sci-fi movies made them out to be. They simply stay where they were very violently born and their immense tidal forces accelerate anything straying nearby into their maws. But black holes are tiny on an astronomical scale and only eat so much at a time. Whatever doesn’t fall directly into their event horizons is whipped around them until it heats up into a glowing accretion disk we can detect. And some of this material gets trapped in the powerful magnetic fields around the black hole and is launched into deep space at 99.9% of the speed of light in the form of highly energetic jets which produce powerful gamma rays. This process seemed to be the same for every black hole observed, but there’s no way to be sure if the black holes affected the jets beyond kinetic energy unless you start comparing gamma ray bursts to one another and plotting them along a trend line.

If the trend is exponential, that means new physics are needed to explain the sudden surges in power as we go up in the jet’s energy and vice versa. But the observed trend between kinetic energy of the jets and the power of the gamma ray bursts is linear, which means that it’s rather likely that the process behind forming the jets is the same across the entire spectrum of known black holes. The black hole’s mass affects how much is can swallow at a time and how powerful the jets it emits could be. The power of the jets affects the observed gamma ray bursts when a new black hole is formed and when it’s in the middle of a large meal consisting of stars and gas floating through interstellar space. So if we know that when we up the jets’ power, we also make the GRB stronger in a predictable way, that tells us that we can more or less confidently scale up what we learn about smaller black holes to their immense siblings, and estimate black holes sizes based on the GRBs’ strength. And that’s very useful for learning more about these prolific and extremely influential gravitational ghosts of giant stars.

See: Nemmen, R., et al. (2012). A universal scaling for the energetics of relativistic jets from black hole systems Science, 338 (6113), 1445-1448 DOI: 10.1126/science.1227416

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alpha centauri bb

After decades of trying to find out whether our closest stellar neighbors have planets we could one day explore, we finally have a confirmation that there appears to be an Earth-sized planet floating around Alpha Centauri B. If we wanted to get really nitpicky and technical, this is not the closest star to us because Proxima Centauri is slightly closer, but for practical purposes, this is a world which could well be within our reach in the next 50 to 75 years. Now for the bad news. We probably wouldn’t want to go there because its orbital period is about three and a half days, so its basically a planet like Venus but even more hellish, with a surface of molten rock and little to no atmosphere to speak of, likely stripped away by the stellar winds. Still, this is very good news because there is the potential for more planets in the Alpha Centauri system. We’ve seen plenty of planets orbiting binary star systems, and recently, even a world orbiting a quadruple one. We just need to keep looking for gravitational tugs on the stars in longer orbital periods.

Hold on a second, how come we can find planets orbiting hundreds of light years away but our nearest neighbors’ planet count was and still is an open question? Well, in this case being really close is a big problem because the starlight is so bright that it effectively obscures the planets in transit, making it extremely difficult to detect them with our current fleet of telescopes. Alpha Cen Bb was found by measuring the drag the planet has on its parent star, something easier to see at closer orbital periods since the drag is greater, and thus more noticeable, closer in. For more detail on how this method worked in this case, see the Bad Astronomer’s explanation. His major takeaway from this detection is that we’re getting closer and closer to finding a second Earth if we’re able to find planets close to our mass in more and more places as we keep on looking, so it’s only a matter of time before we spy Terra Nova. And I can certainly agree with that, but it’s a more exciting idea for me to consider more planets around the Alpha Centauri system, ones on which we could land a probe or even a habitat capable of supporting astronauts.

This would give us a good target for the first interstellar journey and help move really ambitious designs to make such a trip possible off the drawing board and into a lab. Of course I realize it’s very unlikely that as soon as a cooler world is found around our nearest stellar neighbors we will be seeing NASA and the ESA start planning missions to it. And I’m pretty sure that we won’t just take astronauts and launch them on a multi-generational trip there. We’re going to be trying the most radical propulsion methods we can conceive of and the humans who will land on exoworlds are going to be extensively modified, both genetically and mechanically. But despite all this, just having a closer target to explore would be a terrific incentive to get the projects started. If we’re only able to land on planets tens or hundreds of light years away, the mission time and its basic requirements go up by orders of magnitude over a trip to our nearest neighbors for a relatively quick look-see. Well, relatively quick on a time scale of a civilization that is..

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habitable world

According to results from Kepler, there’s another habitable planet just 49 light years away. Well, mostly habitable by something. Gliese 163c is on the higher end of the super-earth label, coming in at between 1.8 and 2.4 times the size of Earth and almost 7 times its mass, and orbiting a red dwarf star once every 26 days. It’s hot, about 60° C hot according to a baseline estimate, but it’s not too hot for a lot of living things. All sorts of extremophiles live in much hotter temperatures on our own world, considering boiling hot caves and toxic vents a cozy home. This is why the press releases from the discoverers of the solar system focused on the potential for microbial or rather simple animal life on Gliese 163c, pointing out that on Earth, no plants or animals can survive for extended periods of time when temperatures soar past 50° C, which would be a cool day on the alien world in question. However, with all due caution, we should consider that what seems to be extreme to us isn’t all that extreme to many other lifeforms and complex life that had billions and billions of years to evolve in very hot conditions could certainly find a way to thrive.

Even more importantly, we don’t know the composition of Gliese 163c’s air, and that could be a critical factor in deciding how habitable we deem it. If its atmosphere is primarily filled with water vapor or has huge concentrations of greenhouse gases, it may as well be another Venus and a hellish place for even the most primitive life. But on the other hand, only small quantities of any greenhouse gases would mean that the planet doesn’t retain very much heat. Water would be a great heat sink as well, and considering that it’s almost certainly tidally locked, the movement of air between the day side and the night side could bring down the overall global temperature and open up some very cool and cozy environments for complex, multicellular life. And as always, if you go deep enough into an ocean, there are bound to be places for life to find a niche, even if the planet is drifting though interstellar space with no sun to warm it. A few hundred meters under the seas of Gliese 163c it could be nice and cool for large aquatic animals to roam in search of food and a mate, though they might have to avoid choppy seas around any equatorial storms fueled by constant evaporation on the day side.

Ideally, the center of the planet’s day side would be a bone dry, perpetual desert constantly in the blinding gaze of its parent star. With no water to evaporate, no cycles of cooling and heating because there would be no night, and nothing but barren rocks, the worst its sun can do is kick up massive dust storms around the equator. That would leave seas, lakes, or even oceans free of constant monsoons. Of course this is pure speculation, but the possibilities are there and we now have a nearby target to better investigate for signs of biology. Next, we can sample its air to better figure out its real average temperature, and try to take a snapshot of what it actually looks like. Its doubtful that we could make out seas or continents with what would most likely be a tiny fraction of a pixel on the screen, but the reflectivity of its clouds or lack thereof could tell us a bit about Gliese 163c’s composition. And that’s the exciting part of astronomy. Every peek we take, every survey we conduct has the potential to show us something new or overturn our notions of what can happen in the cosmos. After all, the world’s top experts thought that the universe was static and infinite until one of them took another look and made a few measurements…

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dark planet

Depending on who you talk to, planets around alien suns are either somewhat rare due to the chaotic nature of planetary formation around infant stars, or even more plentiful than the stars themselves. Since exoplanets are rather small and dim, lost in the glare of their host suns, spotting them takes a lot of time and effort. Direct observation means catching a momentary dip in starlight from an object of indeterminate size at a time that’s random to the observer. If a currently unknown planet orbits its sun every 237 days, how will you know to point your telescope at the right star every 237 days? There just has to be a better way of taking the galactic census so we can figure out what the average solar system looks like, and ultimately, what are the chances one may have the right conditions to host life. And there may be according to a group of astronomers who used a very familiar manifestation of general relativity to escape the normal fuss and bother of exoplanet detection, trying to find planets that orbit a little bit farther from their suns to get a rough measure of solar system sizes.

When we last talked about the physics of wormholes, we looked at microlensing, essentially the distortions in the appearance of an astronomical object caused by the gravity of something relatively small in front of this object in our line of sight bending the fabric of space. Usually we deal with gravitational lensing on the scales of galaxy and galaxy clusters and it’s partially how we know that dark matter exists. At either end of the light distorting spectrum it’s the same mechanism at work. Traveling photons are skewed by the uneven fabric of space and time. So, the researchers posited, if galaxies can distort the appearance of other galaxies and we see stars doing the same thing, what about planets orbiting stars? We know they also bend light in the wake of their gravitational wells, so a planet orbiting at some distance around a star should distort its halo. And so, after watching 100 million stars, they found evidence of exoplanets in orbit around their parent suns exactly as general relativity predicted would happen if they were there. Of course this is all easier said than done.

Since a star pumps out so much light and the planets have to orbit at just the right inclination to be spotted in the act of disturbing the halo, the 100 million stars had to be narrowed down to just 500 promising ones, and those 500 had to be watched for five long years until ten cases of direct microlensing were finally seen. But all that effort didn’t seem to bring consistent data since the results seem all over the place. According to the tally, between 6% and 23% of stars seem to host a Jupiter-like world, between 23% and 74% have a Neptune-like body, and between 25% and as many as 97% might have a terrestrial planet around them. As the planet size gets smaller, the uncertainty increases wildly, so much so as to be almost meaningless for terrestrial worlds which are the ultimate goal of all planet hunters. The exoworlds are just too dim, too far away, and too small to register prominently on our existing instruments, and although the study does imply that pretty much all stars have a solar system of some sort, it can’t actually tell us anything definitive about what sort of planet we could usually expect. Going by this survey, it could be anything from a turbulent gas giant to Earth 2.0.

Don’t get me wrong, trying to use microlensing to find the statistical distribution of planets is a terrific idea. It’s just that the universe keeps on placing interesting things too far away for us to spot with out current tools. We could even try this trick again with better equipment and hyper-sensitive telescopes to see if we can get more predictive and accurate tallies. However, it seems that until then, the candidate worlds seen by Kepler, and in the future, the Terrestrial Planet Finder, will provide us with the most accurate and predictive sampling of our galactic neighborhood since they can point to actual planets with an accuracy I doubt we could get from even the most precise measurements of planet-created microlensing manifesting around distant alien suns. This sort of survey would give us a more accurate picture of planetary distribution across the galaxy and allow us to build an accurate picture of a typical alien solar system. With such a model, we could look at any random star and have a decent idea of what we should expect to see orbiting it and at approximately what distances from it so we can better time our telescopes’ observations in the hunt for another planet that hosts intelligent life.

See: Cassan, A., et al. (2012). One or more bound planets per Milky Way star from microlensing observations Nature, 481 (7380), 167-169 DOI: 10.1038/nature10684

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Bizarre things are lurking out there in our universe. Titanic beasts born as space and time shatter under more than enough energy to be felt across thousands of light years, beasts with the power to devour stars whole as they whip the very fabric of reality around their gaping maws like their plaything and dictate the speed at which stars more than 4,000 light years away move. This is not an exaggeration or some sort of horror story. This is very real, and in fact, refers to two objects roughly 330 million light years away, supermassive black holes that weigh in at nearly 10 billion solar masses, and whose event horizons span the diameter of our solar system seven times over. Billions of years ago, they formed from giant maelstroms and have now comfortably settled to rule domains with a trillion stars each, the elliptical galaxies of NGC 3842 in the Leo Cluster and NGC 4889 in the Coma Cluster. Just think about this for a second. Space and time were torn open and now contain tens of billions of solar masses of superheated energy chaotically whipping around itself as it mocks physics.

Considering the the last heaviest confirmed supermassive back hole was 6.4 billion solar masses, this pair easily shatters the previous record thanks to a perfect storm of collisions and implosions. It’s not a very likely scenario for them to have come from hypernovae, since even the most massive stars we could see existing could not give them a close enough head start to expand to their gargantuan heft. Far more likely was a giant implosion of immense, dense clouds of hydrogen and helium gas in what would end up as the cores of new galaxies. As they swallowed countless nebulae and stars around them and those which strayed too close to them during collisions with other galaxies during their quasar days, they would grow quickly, and being at the centers of elliptical galaxies, the type which tends to house the most stars, feed the biggest black holes, and undergo the largest and most protracted collisions, helped add even more to their gargantuan bulk. We could only imagine the sheer size and power of the jets that must’ve emanated from them during these galactic pile- ups, spiraling along twisted, hyper-charged magnetic lines for more than 100,000 light years.

So how big are the results of all this galactic turmoil really? How can we put them in perspective? If we could imagine a ladder where each rung represented a solar mass, or nearly 330,000 times the mass of our world and everything on it, it would stretch halfway to the Moon. If you were to count each solar mass aloud, it would take you over 300 years to finish counting nonstop. Well, actually it would take your great-great-grandchild his or her entire life to finish what you started. And let’s not even start going down to Earth masses because then, the numbers become absolutely meaningless to even try to imagine. It absolutely blows my mind that bizarre things like this can even exist, much less be actually detected hundreds of millions of light years away. If we were to run the numbers on how long they’ll last until they finally evaporate from Hawking radiation, we will get an absolutely mind-boggling number, placing their lifespans as stretching to the darkest, coldest phases of our universe, a time when nothing will be left but the remnants of supermassive black holes and things like stars, planets and galaxies are a thing of the nearly unthinkably deep past.

But wait, if those horrifying monsters are some 330 million light years away, how can we know if they actually exist? We look at the light of the stars in a galaxy and calculate their orbital velocities. The faster the stars at or near the core of the galaxy being watched orbit around a target region, the more likely it is that they’re circling a black hole. In NGC 3842 and NGC 4889, stars spun so quickly around such a small area that the only way to explain their motion were enormous black holes. This is the same method which found the last record holder and the astronomers who used it to find these titans aren’t done yet. If they pick their targets wisely, they could find even larger supermassive black holes out there. Again, it’s simply mind-blowing with what nature comes up when left to its own devices. When they were first proposed as a result of Albert Einstein’s equations, they were dismissed as far too outlandish to possibly exist. Today we know that not only do they exist, but that they come in all masses, live at the heart of virtually every galaxy, and that one day they may inherit the universe as we understand it. And we can also see that their weirdness and longevity truly demand our respect…

See: McConnell, N., et. al. (2011). Ten-billion-solar-mass black holes at the centres of giant elliptical galaxies Nature, 480 (7376), 215-218 DOI: 10.1038/nature10636

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Whenever you tell someone that you have trouble believing in an omniscient, omnipresent, invisible deity who created the universe by its sheer will, but you’re certain that there is alien life elsewhere in the cosmos, oddly, you will get surprised stares. How can you believe that aliens are out there? No one has seen them so what evidence do you have that they might exist? Well, besides the fact that for an alien to exist would take far fewer leaps of logic and far fewer assumptions, it’s because we keep finding the chemistry of life floating in deep space in nebulae and asteroids, and the recent set of observations from our telescopes keep turning up the signals of potential places for alien life to exist. While the discovery of Gliese 581g might have turned out to be less than meets the eye at first, we now have a confirmed detection of a seemingly hospitable place for a biosphere, the terrestrial world of Kepler-22b. It orbits a Sun-like star every 290 days, placing it firmly into the habitable zone where temperatures should be ideal for liquid water given an atmosphere of the right density, and it’s only some 2.4 times bigger than Earth, firmly in the realm of the kind of planets we want to find.

Of course we still don’t know a lot of things about Kepler-22b. Without a good idea of its composition, we can’t say what its gravity is like or what gases float in its atmosphere. Plenty of oxygen would immediately signal an abundance of life there. but even if we don’t detect oxygen, it doesn’t mean that its lifeless. After all, oxygen is a toxic and corrosive gas which quickly breaks down without being steadily added into an atmosphere by biota, and we now know that life can thrive on other gases, including methane and carbon dioxide. Just as long as a liquid is present as a solvent, some form of self-perpetuating chemistry can arise and sustain itself. Because the planet is about 600 light years away, even if it has a glowing alien city covering half of its hemisphere, we wouldn’t be able to see it since all of Kepler-22b would be only a tiny smidgeon of a single pixel in our highest resolution images, and without an obvious flag like a significant amount of atmospheric oxygen or other hard to sustain gas, we’d never really know whether Kepler-22b hosts life or not without actually going there to find out firsthand. However, even knowing that such a planet actually exists and shows so much promise is quite thrilling in and of itself, especially knowing that it’s been detected directly three times, unlike Gliese 581g.

True, we shouldn’t imagine it as an alien Eden yet, but it’s hard not to get excited given what we know about it so far, especially given the fact that it’s not the only planet we know of close to or in its parent star’s habitable zone. In fact, SETI is now calibrating its telescopes to include Kepler data and trying to listen for any trace of artificial activity leaking into space from the most promising worlds in this growing planetary catalog. We have been dillgently trying to see if we’re not alone for the last century or so, and we’re now gaining the tools to take a much deeper and more thorough look at our stellar neighborhood to see if there’s anyone out there. It’s not an area of research we should take lightly and we should continue to look for alien life within our solar system as well, with Europa being one of the best candidates for an extraterrestrial biosphere. Knowing that we’re not a lonely spark of life in the cosmos for a fact may not change life as we know it nowadays, but maybe one day, it may help us to see ourselves not as citizens of countries competing for dominance, but as a single species living on a fragile little world, Sagan’s pale blue dot, a species which needs to look aim skyward and refuse to stay content with having a short lifespan and its feet planted firmly on the ground. Our distant ancestors were explorers and inventors, and we owe it to them to continue their legacy, not wallow in the mundane minutia of post-industrial life, trapped under the heel of bureaucrats bereft of any vision or sense of wonder.

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At the rate we’re going, it seems that the first target for one of our future interstellar spacecraft will just have to be the Gliese 581 system. Beyond the initial hype generated by the announcement of planet 581g and a very deflating set of calculations showing that it may have just been a mirage, there were still planets with a little potential for life as we can understand it. This is why when discussing the practicality of colonizing the solar system in question, I brought up two worlds which seem to have faded from our collective memories. Now, it seems that one of these worlds, 581d, may actually be the terrestrial, habitable planet for which astronomers have been searching. Originally thought too cold for liquid water, the planet was put on the back shelf until an advanced climate model ran by French scientists showed that such a world could actually have oceans, rain, and stay warm enough to avoid having its night side frozen solid if it were tidally locked in its orbit. How? Well, as it turns out, it all comes down to sunlight, or rather to the right wavelength of sunlight. For a big planet with an atmosphere rich in carbon dioxide, a red star may actually be an enabler of a dynamic, warm climate…

When astronomers first considered Gliese 581d as a candidate for habitability, they thought that much of the light from its parent star would be reflected back into space as happens on our world. However, the light we get from the Sun has a shorter wavelength and gets scattered when it meets air molecules and other small, fine particles in our atmosphere. This phenomenon called Rayleigh scattering and it’s what gives our skies a bluish tint. When dealing with longer wavelengths, like you’d find coming from oh say a red dwarf star, the red light scatters less and more of it reaches deeper into the kind of thick carbon dioxide atmospheres that seem common for large, rocky planets. As a result, the skies of Gliese 581d would have a murky reddish glow and the conditions would support a water cycle, which we know to be a key for enabling life. If this model is right, it would not only mean that a planet just over 20 light years away is habitable, but that it’s probably inhabited by something since it’s difficult to imagine a watery world without life. After all, once upon a time Earth’s air had a lot of carbon dioxide and other gases we consider noxious and deadly today while its oceans were home to a countless variety of bacterial colonies thriving for billions of years, reproducing and growing away while much of the planet was erupting away with vast lava flows and toxic plumes that made the surface unlivable.

Whether 581d is tidally locked or not could determine what could live there and where we could find traces of those living things. Having a perpetual day side could allow for constant photosynthesis for organisms which would form the base of food chains in which the lit hemisphere is the central hub of all activity. Life could exist on the night side as well, but if photosynthesis didn’t evolve on 581d, the base of the food chains would be an assortment of bacteria feeding off thermal vents on ocean floors. Were the planet to rotate around its axis and have an actual night and day cycle, we could expect living things to be more widespread as more habitats will be available to them. Either way, the entire planet would be warmed thanks to wind circulation, but with direct sunlight across 581d a greater variety of organisms may have chances to establish new footholds to escape predation or to take full advantage of abundant resources. This is after all how we think all our forests started out, as primitive plants which grew with no competition, feeding on sunlight and carbon dioxide. If 581d were to repeat this evolutionary step, we could find traces of some sort of biological activity in its atmosphere. This is all conjecture, of course, and further observations will need to be made to figure out more about this world, but since we now know its potential, we should devote some time and resources to study it.

Again, it should be noted that as far as interstellar objects go, Gliese 581 is very close by, close enough to be of interest to some sort of mission at some point in the future. Should our hunches turn out to be right, there’s a very strong case to be made for at least trying to send a probe there. It may take a very long time to come up with the required technology to make the trip quickly enough, but with a very reasonable target in sight, it may just motivate enough space agencies, scientists, and engineers to rise to the challenge and create the brand new generations of computers, engines, reactors, and materials required for the journey. Maybe discovering and confirming that 581d can support life is exactly what we need to motivate future space explorers. Though we also need to be very cautious not to get too attached to the idea that 581d must be habitable because the models may be wrong and we don’t want to let confirmation bias take over the astronomers’ observations. It’s fun to speculate and the models seem very promising thus far, but at the end of the day, real data will need to have the last word on whether Gliese 581d is really habitable or not.

Wordsworth, R., et al. (2011). Gliese 581d is the first discovered terrestrial-mass exoplanet in the habitable zone The Astrophysical Journal, 733 (2) DOI: 10.1088/2041-8205/733/2/L48

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