Archives For exoplanets

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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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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Quite a bit of scientific literature on astrobiology is filled with references to very exacting criteria for exoplanets capable of sustaining alien ecosystems. They have to be just the right distance from their suns, have the right kind of atmosphere, fall in the right temperature range, and hopefully, have a large stabilizing moon to counter their constant orbital wobbles from creating ice ages and migrating ice caps around the poles. But as we see more exoplanets out in the wild and do more accurate simulations, we’re finding that a lot of these constraints are starting to fall away. It seems that life could have a chemical basis in a liquid ethane lake, and might not even need a star to host a habitable ocean. And now, it looks like it might not even need a big moon to keep its axis more or less steady over the eons, allowing complex life to evolve without swift climate changes. It’s a nice to have for a flourishing ecosystem, certainly, kind of like having traction control in your car is a really nice and helpful feature, especially on ice and wet roads. But you can certainly get by without it if you had to, just as potential alien life on exoplanets without a big moon like ours could cope with an occasional climate shift.

It all started with a simulation in 1993 which showed that without the Moon, our planet could wobble as much as 85° on its axis which means that long term climate patterns humans enjoyed for many thousands of years just wouldn’t be possible. On geologic timescales, we’d be looking at mass extinctions on a far more frequent basis than we see in the fossil record as life would struggle to adapt. Planets are not exactly dainty things and all this would happen over tens of millions of years, but if we consider that Earth was home to living things for roughtly 3.5 billion years or so, these are fairly rapid and extreme changes which would test evolution’s ability to produce complex multicellular organisms when the selective pressure is to stay small and very efficient. So if an alien planet wants to be home to a massive, complex, and diverse ecosystem, it better be just as stable as we are, wobbling only by 2.6° at most thanks to our massive Moon, right? Turns out that that’s not the case at all because the range found in the original study is actually exaggerated by more than a factor of two. In fact, if the Moon was never formed, we would’ve wobbled between an axis of 10° and 50° over 4 billion years. Not a bad improvement on the originally predicted arc that could turn our planet sideways, then upright again.

And there’s another surprise. Within those 4 billion years without the Moon’s influence, there are stable cycles lasting for 500 million years. While the planet’s orbital wobble would be far more extreme than we have now, it wouldn’t be anywhere near 85° off axis. A more accurate figure seems to be 15° or so, which would entail the occasional massive ice age followed by rapid warming periods, but on timescales that would span almost all the evolutionary changes that lead from giant sea scorpions, to dinosaurs, to us. How can this kind of stability be possible if we didn’t have a lunar rudder? Well, generally a planet wobbles due to the very slight tugs from other objects in the solar system accumulating over millions and millions of years. But the same tugs that will send a planet wobbling could also be corrective and the occasional comet or asteroid impact could nudge the planet in another direction by countering a tug from a distant world or a passing comet. It all ads up to a slow, almost reluctant wobble rather than uncontrolled tumbling through space. And if the planet happens to be in a retrograde orbit (orbiting in the opposite direction of its siblings), their wobbles are in the same range as our current axial oscillations. That means we can bravely widen our search to include rocky worlds without large, stabilizing moons as a potential home for macroscopic aliens, if not other intelligent life.

See: Lissauer, J., Barnes, J., Chambers, J. (2012) Obliquity variations of a moonless Earth Icarus, 217 (1), 77- 87 DOI: 10.1016/j.icarus.2011.10.013

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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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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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If you think of a solar system as a stellar family, you should probably be aware that this sort of family is highly dysfunctional, especially in its early years. Planetoids viciously slam into each other, and gas giants can and do throw out smaller, rocky worlds when they settle into eccentric orbits. When the solar system finally begins to settle down, it’s made up of survivors and a few of the star’s children may be ejected into interstellar space to wander the cosmos for eons to come, bombarded by sterilizing cosmic rays and with atmospheres frozen solid without the heat of a star. Maybe one day they’ll fly by stars at just the right angle to be captured and orbit their adopted sun until it dies. But odds are that they’re probably going to remain frozen spheroids of ice that haunt the voids between stars. Surely they’re doomed to lead a dark and lifeless existence, illuminated only once in a great while by a passing sun, never hosting so much as a bacterium, right? Well, maybe these odd outcasts aren’t doomed to be icy, lifeless rocks after all. Depending on how their atmospheres will freeze and the compositions of their innards, they may just be home to a stealthy ecosystem fed by their cores’ heat…

Of course there are some significant catches for that to happen. An interstellar alien biosphere would have to start on a planet already somewhat hospitable to life and rich with water and carbon dioxide. Ideally, a planet ejected from its solar system would already have given rise to primitive bacteria and as it drifts outward, it will get colder and colder at what we would consider an alarming rate, but to which bacteria could well adapt. As the atmosphere and several kilometers of ocean freeze into a thick, radiation resistant shell, the bacteria still have places to live, especially if they travel deeper towards the ocean floor, where the thermal vents will keep ejecting plenty of energy and nutrients to sustain vast colonies, and maybe even multi-cellular life, much like we see on our very own planet around deep sea volcanic smokers. As long as the planet itself is volcanically active, it could use the heat generated by the decay of naturally occurring radioactive isotopes of elements like potassium, uranium, and thorium in its core to warm deep oceans covered by thick layers of ice, which would act a insulators and create some convection, helping to stir up life-sustaining nutrients floating in the ocean’s layers. Depending on the size of the planet, the radioactive decay could keep the oceans hospitable for one to five billion years, putting it in the same league with many planets still orbiting their stars.

So how big should a planet be to stay warm even after it’s been sent out of its solar system? If it has a similar composition to Earth, it should ideally be about 3.5 times as massive. That extra heft means more rock to act as an insulator for the decay of potassium-40, uranium-238 and thorium-232, a thicker blanket of ice on top, and more water to contain an active biosphere. But if a planet’s atmosphere is rich with carbon dioxide, it can reach its steady state easier and could theoretically be as small as 0.3 Earth masses while still holding on to a warm and hospitable ocean. Of course warm is somewhat relative in this case because the steady state in question is 260 K, or -13.5 °C at the point between the end of the ice sheet and the top layer of the ocean. For a balmy world like ours that’s pretty cold, but it’s certainly not bad at all for a sun-less planet barreling through interstellar space, keeping its water liquid by pressure and bottom-up convection. And considering that it will also spew countless tons of nutrients and emit plenty of heat from its volcanic vents, we might even go as far as trying to guess whether life could evolve on a rogue planet after it’s been ejected. Since all the basics for a biosphere would already be there, right at the warm and nutrient-rich bottom of its oceans, couldn’t life stand a decent chance of appearing and thriving like it has in similar conditions here on Earth? Creatures like worms and nematodes, along with alien equivalents to arthropods could certainly call a place like that home.

However, there’s a little twist to consider. Imagine a super-Earth with an extremely deep ocean, much deeper than anything we will see in our solar system, and suspect may be on the ocean floor of planet GJ 1214b if it is an ocean world like we think. The immense pressures at the sea bed could exceed 80,000 atmospheres, or about 1.1 million psi, forming an exotic form of matter known as Ice VII. With deep enough oceans, water can be compressed to a near-solid state and make it extremely difficult, if not virtually impossible, for life to evolve around nutrient rich vents, or restrict it to liquid layers which would have access to volcanic vents at a far lower depth, where water could still be warmed and convection can occur. It would be an unusual scenario since it means that a frozen world up to 7 Earth masses wandered close enough to its parent sun to melt more than hundred miles of ice and create an extremely thick, water vapor rich atmosphere which would cause a strong greenhouse effect, then somehow get ejected from the system and have that thick atmosphere freeze over its surface. But it is a plausible scenario, and in a universe where we might find alien life on a rogue interstellar snowball of a world, it probably wouldn’t be the weirdest thing that might’ve happened…

See: Dorian S. Abbot, Eric R. Switzer (2011). The Steppenwolf: A proposal for a habitable planet in interstellar space submitted to Astrophysical Journal Letters arXiv: 1102.1108v1

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After looking at a tiny fraction of the stars in our sky, Kepler found over a thousand candidate planets around alien suns and is starting to give us a more accurate census of worlds beyond our solar system. And keep in mind that those 1,235 exoplanet candidates, detected over four months from a survey of 156,000 stars, will be just the tip of the iceberg. Since the telescope looks for transiting planets, worlds that pass in front of the star they orbit and cause a slight dip in the light Kepler sees, a few months only give us a quick peek. If there’s an alien counterpart to this mission, it would have to monitor the Sun for an entire year to see us since that’s our orbital period, so to get a true survey of exoplanets, Kepler would need to stare at the same patches of sky for years on end, and even then, we would know that planets may be orbiting their stars at angles which make a transit detection from our vantage point impossible, and that our data will always be incomplete. But despite the fact that we’ll probably never get a precise tally of exoplanets, what Kepler found so far is encouraging.

First off, rocky planets either as big as ours or super-Earths make up 29% of the sample. So much for all the popular science shows’ concerns that we can’t seem to find worlds more like ours in the night sky. Of course most of the exoplanets found before this announcement were gas giants; they were the only worlds massive enough to accurately detect by measuring the gravitational tug on alien suns. Small, rocky worlds lack the heft they’d need to exert enough of a tidal pull on their stars to clearly and consistently register on our instruments, and that means watching for them to transit between the target star and a telescope’s mirror is the only good way to detect them. So if terrestrial planets make up close to a third of our first quick survey, that means there are plenty of planets like Earth, Mars, and Venus out there, along with their much larger versions, which could be up to seven times the mass of our world; any more than that and it’s thought that gravity would cause such a huge and heavy planet to crack under its own bulk. I also think it’s worth pointing out that a bigger planet will be easier to see since it would block a lot more starlight and would be easier to confirm, so the survey’s bias towards larger and heavier worlds may be more of an instrument issue than just the way things are.

Speaking of bias towards larger and heavier worlds, it was surprising to see Neptune-sized planets making up slightly more than half of all detected candidates. Again, I would like to chalk this up to the relative ease of detecting for a large world, but the sheer amount of planets in this size category makes me wonder. Going up to the heavyweight planetary division, even with all the odds of being easily found on their side, alien Jupiters made up just 13% of the tally, which makes perfect sense since massive worlds need to collect plenty of gas and dust during formation, and with the turbulent environment of a young solar system, only a few will make it to the upper echelon of gas giant-hood. Now, mind you, this distribution doesn’t necessarily provide accurate models of planetary populations across the cosmos, but does give us a few hints and confirms several basic ideas we’ve had all along. There are plenty of rocky worlds, huge gas giants like Jupiter would be the minority in most solar systems, and there are lots of smaller gas planets. And there are also some 54 candidates in the habitable zones of their stars, four of them Earth-sized and the rest going up in size from there. We might have four second Earths on our hands if the data holds, and when we consider that super-Earths and moons of gas giants with a thick enough atmosphere could also host life, the potential of this survey is just amazing to say the least. We can’t say we found extraterrestrials, but we may have found 54 places where they live.

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All right ladies and gentlemen, here’s some real scientific content to discuss. Astronomers at the ESO’s huge observatory in Chile managed to find a planet born in another galaxy and confirm that indeed, other galaxies should also have planets orbiting their parent stars just like we have in our stellar neighborhood. It seems to be a pretty safe if not obvious assumption, but in astronomy, and in all of science, nothing could be assumed to be certain without detailed observations to back it up. But hold on, you might say, how could any telescope have enough resolution to focus on an individual star in a galaxy and make out a planet orbiting it? We have a whole lot of problems doing that in our own galaxy. And you’d be right. The planet from another galaxy is really a part of our very own Milky Way. It’s just that this planet is in a stream of stars left over from a dwarf galaxy that was torn apart by the Milky Way’s gravity. Today, it’s just 2,000 light year from Earth, putting it close enough to detect by measuring its tug on its parent star, HIP 13044. Oh and by the way, this planet it about to be eaten.

You see, HIP 13044 is an old star and it has already expanded into a red giant in its recent past before quickly contracting and fusing helium in its core. It’s due to re-expand again, this time swallowing the closely orbiting planet which most likely fell into its current 16 day orbital period at some point during the star’s first expansion into a red giant. The planet itself is already pretty scorched, but as its star grows closer and closer, it will start vaporizing away, the incoming solar winds stripping off countless tons of gas. Depending on how long it will take HIP 13044 to re-expand, the planet may be stripped to its core before it’s swallowed up. Alternatively, the star’s outer layers could reach it so quickly, it will be engulfed whole. If there were any other planets orbiting a little closer to HIP 13044, they were already incinerated during the star’s first swell into a red giant, cooked by radiation and smelted down into a stream of metallic vapor. Just like most of our inner solar system will be in the next five billion years when the Sun goes through the same exact process and quite possibly devours us and the Moon unless the combination of gravitational tugs and lower surface gravity of the Sun as a red giant manage to push us into a much higher orbit in which we’ll barely survive.

Not only is HIP 13044 and its planet showing us that the same things we know happen in this galaxy happen in others, they’re also giving us a peek into our own distant future, a future when to imagine the Earth, you will have to picture a world that no longer has identifiable continents and on which the bizarre landscapes hidden from us under miles of water today, become the planet’s biggest and most volcanically active deserts. A future when the sun fills up most of the sky at noon. A future in which rivers and oceans of glowing lava flow across the planet’s surface as the crust is being melted and reshaped by the raw heat of our parent star. This future has already come and gone for any other world that may have been floating around HIP 13044, and it’s about to play out for its Jupiter-sized planet. And when it does, we’ll know that we’ve really accomplished something very important with astronomy. We’ve learned where we’ve come from, where we are, where we’re going, and how it will all end for the place we call home. And we also now know that the same thing is happening in other galaxies around us on a daily basis, a cycle of birth and death that will continue for trillions of years, until the very last star finally goes out and the universe enters its second dark age…

[ illustration by Paul CZ ]

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