2 years ago the Kepler probe was dealt a critical blow. Out of 4 reaction wheels, the devices which keep the telescope pointed in the right direction, only 2 remained functioning. This meant that the telescope was no longer able to maintain the level of precision required to continue its planet hunting mission. However there was a bold plan to continue Kepler’s mission, albeit in rather different capacity. Kepler could use the solar pressure exerted by our sun as a third reaction wheel, allowing it to continue imaging the sky and looking for planets. It wouldn’t be able to look at the same piece of sky for the entire time however and would be limited to viewing periods of approximately 80 days each.
Whilst this was a significant downgrade in Kepler’s abilities it was a far better option than just retiring the spacecraft completely. In its previous incarnation Kepler was able to track hundreds of thousands of stars continuously, allowing us to detect numerous planets orbiting their parent stars. In its current incarnation Kepler will only be able to detect planets with shorter orbits which are unlikely to be the Earth-like ones we’re all hoping for. Still even in that reduced capacity Kepler has been able to identify no less than 100 new exoplanets with over 200 additional candidates awaiting confirmation by other methods. For a telescope that may have been written off that’s an amazing accomplishment, but it doesn’t just stop there.
As the above diagram shows Kepler has to reorient itself every so often so that light from the sun doesn’t enter the telescope (this would damage its sensors). Not all of these orientations are good for looking for exoplanets however and so Kepler has been put to other uses. Several of the viewing periods have been dedicated to looking at planets within our own solar system, giving us insights into their behaviour like we didn’t have before. It recently spent 70 days observing the weather on Neptune and the motion of its moons, the longest observation of the planet to date. Additionally another observation period is being dedicated to doing a similar investigation on Uranus.
Like I’ve said before second chances with space missions are rare and it’s incredibly heartening to see Kepler producing these kinds of results 2 years after its reaction wheels failed. Whilst these might not be the exact results we’re after they’re still invaluable pieces of data that will help broaden our understanding of both our universe and galactic backyard. I’m sure that we’ll continue to see great things from Kepler and, hopefully, many more exoplanets.
As far as we know right now we’re alone in the universe. However the staggering size of the universe suggests that life should be prevalent elsewhere and we (or they) have the unenviable task of tracking it (or us) down. We’re also not quite sure to look for as whilst we have solid ideas about our kind of life there’s no guarantees that they hold universally true across the galaxy. So when it comes to observing phenomena the last reason researchers should resort to is “aliens did it” as we simply have no way of verifying that was the case. It does make for some interesting speculation however like with the current wave of media hysteria surrounding KIC 8462852, or Tabby’s star as it’s more informally called.
KIC 8462852 was one of 145,000 stars that was being constantly monitored by the Kepler spacecraft, a space telescope that was designed to directly detect exoplanets. Kepler’s planet detection method relies on a planet transiting (I.E. passing in front of) its parent star during its observation period. When the planet does this it ever so slightly drops the brightness of the star and this can give us insights into the planet’s size, orbit and composition. This method has proven to be wildly successful with the number of identified exoplanets increasing significantly thanks to Kepler’s data. KIC 8462852 has proved particularly interesting however as its variation in brightness is way beyond anything we’ve witnessed elsewhere.
Indeed instead of the tiny dips we’re accustomed to seeing, an Earth-like planet around a main sequence star like ours produces a chance of about 84 parts per million, KIC 8462852 has dipped a whopping 15% and 22% on separate occasions. Typically this isn’t particularly interesting, there are many stars with varying output for numerous reasons, however KIC 8462852 is a F-type main sequence star which is very similar to ours (which is a G-type if you’re wondering). These don’t vary wildly in output and the scientists have ruled out issues with equipment and other potential phenomena so what we’re left with is a star with varying output with no great explanation. Whatever is blocking that light has to be huge, at least half the width of the star itself.
There are a few potential candidates to explain this, most notably a cloud of comets on an elliptical orbit that happens to transit our observation path. How that exactly came to be is anyone’s guess, and indeed it would be a rare phenomenon, but it’s looking to be the best explanation we currently have. A massive debris field has currently been ruled out due to a lack of infrared radiation, something which would be present due to the star heating the debris field. This has led to some speculation as to what could cause something like this to happen and some have looked towards intelligent life as the cause.
How could an alien race make a star’s output dip that significantly you ask? Well the theory goes that any sufficiently advanced civilization will eventually require the entire energy output of their star in order to fuel their activities. The only way to do that is to encase the star in a sphere (called a Dyson Sphere) in order to capture all of the energy that it releases. Such a megastructure couldn’t be built instantly however and so to an outside observer the star’s output would likely look weird as the structure was built around it. Thus KIC 8462852, with its wild fluctuations of output, could be in the process of being encased in one such structure for use by another civilization.
Of course such a hypothesis makes numerous leaps that are not supported by any evidence we currently have at our disposal. The research is thankfully focused on finding a more plausible explanation, something which we are capable of finding by engaging in further observations of this particular star. Should all these attempts fail to explain the phenomena, something which I highly doubt will happen, only then should we start toying with the idea that this is the work of some hyper-advanced alien civilization. Whilst the sci-fi nerd me wants to leap at the possibility of a Dyson sphere being built in our backyard I honestly can’t entertain an idea when I know there are so many other plausible options out there.
It is fun to dream, though.
When it comes to exoplanets the question that I often hear asked is: why are they all largely the same? The answer lies in the methods that we use for detecting exoplanets, the most successful of which is observing the gravitational pull that planets have on their host stars. This method requires that planets make a full orbit around their parent start in order for us to detect them which means that many go unnoticed, requiring observation times far beyond what we’re currently capable of. However there are new methods which are beginning to bear fruit with one of the most recent discoveries being a planet called 51-Eridani-b.
Unlike most other exoplanets, whose presence is inferred from the data we gather on their parent star, 51-Eridani-b is the smallest exoplanet that we’ve ever imaged directly. Whilst we didn’t get anything like the artist’s impression above it’s still quite an achievement as planets are usually many orders of magnitude dimmer than their parent stars. This makes directly imaging them incredibly difficult however this new method, which has been built into a device called the Gemini Planet Imager, allows us to directly image a certain type of exoplanet. The main advantage of this method is that it does not require a lengthy observation time to produce results although like other methods it also has some limitations.
The Gemini Planet Imager was built for the Gemini South Telescope in Chile, the sister telescope of the more famous Gemini North Telescope in Hawaii. Essentially it’s an extremely high contrast imager, one that’s able to detect a planet that’s one ten millionth as bright as its parent star. Whilst this kind of sensitivity is impressive even it can’t detect Earth-like planets around a star similar to our sun. Instead the planets that we’re likely to detect are young jupiter planets which are still hot from their formation being far more luminous than a planet typically is. This is exactly what 51-Eridani-b is, a fiery young planet that orbits a star that’s about 5 times as bright as our own.
Equally as impressive is the technology behind the Gemini Planet Imager which enables it to directly image planets like this. The first part is a coronagraph, a specially designed interference device which allows us to block out the majority of a parent star’s light. Behind that is a set of adaptive optics, essentially a set of tiny mirrors that can make micro-adjustments in order to counteract atmospheric distortions. It has to do this since, unlike space based telescopes, there’s a lot of turbulent air between us and the things we want to look at. These mirrors, which are deformable at the micro level using MEMS, are able to do this with incredible precision.
With the successful discovery of 51-Eridani-b I’m sure further discoveries won’t be far off. Whilst the Gemini Planet Imager might only be able to discover a certain type of planet it does prove that the technology platform works. This then means that improvements can be made, expanding its capabilities further. I have no doubt that future versions of this technology will be able to directly image smaller and smaller planets, one day culminating in a direct image of an Earth-like planet around a sun-like star. That, dear read, will be a day for the history books and it all began here with 51-Eridani-b.
Whenever I think of a tidally locked planet, like say Mercury, the only image that comes to mind is one that is barren of all life. You see for tidally locked systems the face of the smaller body is always pointing towards the larger one, like our Moon is towards Earth. For planets and suns this means that the surface of the tidally locked planet would typically turn into an inferno with the other side becoming a frigid wasteland, both devoid of any kind of life. However new research shows that these planets might not be the lifeless rocks we once thought them to be and, in fact, they could be far more Earthlike than we previously thought.
Scientists have long theorized that planets of this nature could potentially harbour a habitable band around their terminator, a tenuous strip that exists between the freezing depths of the cold side and the furnace of the hot side. Such a planet wouldn’t have the day/night cycles that we’re accustomed to however and it would be likely that any life that evolved there would have adapted to the permanent daylight. There’d also be some pretty extreme winds to contend with as well due to the massive differences in temperature although how severe they were would be heavily dependent on the thickness of the atmosphere. Still it’s possible that that little band could harbor all sorts of life, despite the conditions that bookended its environment.
However there’s another theory that states that these kinds of planets might not be the one sided hotbeds that we initially thought them to be. Instead of being fully tidally locked with their parent star planets like this might actually still rotate thanks to the heavy winds that would whip across their surface. These winds would push against the planets surface, giving it enough rotation to overcome the tidal locking caused by the parent star’s gravity. There’s actually an example of this within our own solar system: Venus which by all rights should be tidally locked to our Sun. However it’s not although it’s extremely long days and retrograde rotation (it spins the opposite way to every other planet) hints at the fact that its rotation is caused by forces that a different to that from every other planet.
Counterintuitively it seems that Venus’ extremely thick atmosphere might be working against it in this regard as the modelling done shows that planets with thinner atmospheres would actually experience a higher rotational rate. This means that an Earthlike planet that should be tidally locked would likely not be and the resulting motion would be enough to make the majority of the planet habitable. In turn this would mean that many of the supposedly tidally locked planets we’ve discovered could actually turn out to be habitable candidates.
Whilst these are just beautiful models for now they can hopefully drive the requirements for future craft and observatories here on Earth that will be able to look for the signatures of these kinds of planets. Considering that our detection methods are currently skewed towards detecting planets that are close to their parent stars this will mean a much greater hit rate for habitable candidates, providing a wealth of data to validate against. Whether we’ll be able to get some direct observations of such planets within the next century or more is a question we won’t likely have an answer to soon, but hopefully one day we will.
In the short time that I’ve been enamoured with all things space our understanding of the universe has changed significantly. Just a few years ago we had no idea how common multi-planet systems like our own were but today we know that a star is far more likely to have several planets than just a few. At the same time we’ve discovered so many more exoplanets that their discovery is now just routine and the count has tripled from the couple hundred to well over 600 confirmed discoveries (not including the multitude of current candidates). At the same time our understanding of how planets form has also been called into question and today brings news that may just turn our understanding on its head yet again.
Astronomers at the Kavli Institute for Particle Astrophysics and Cosmology released a paper back in February that detailed a very interesting idea. Using the observable effects of gravity in our galaxy combined with the observable mass (detected via microlensing events) they’ve deduced that there needs to be many more planets than what can be accounted for. What’s really curious about these planets is that they would have formed without a parent star:
But how can this be? Every star can’t have tens of thousands of planets ranging from Pluto-sized to Jupiter-sized. This planetary “excess” actually suggests the existence of planets that were born without a star – nomad planets. These planetary vagabonds somehow went through the planet-forming process in interstellar space, not in the dusty proto-planetary disk surrounding a young star.
This astonishing number was calculated by extrapolating a dozen “microlensing” events of nomad worlds passing in front of distant stars. When these nomad planets drifted in front of distant stars, they briefly focused the starlight with their gravity, causing the star to brighten. This brightening was captured by astronomers and the microlensing events could be analysed to reveal the characteristics of the nomad planets.
The idea of planets forming sans a parent star is an interesting one as it turns our current ideas of planet formation on their head. The generally accepted idea of planet formation is that a large accretion disk forms a star first, sweeping away a lot of matter away from it. After that the left over accretion belt begins coalescing into planets, asteroids and other heavenly bodies. Nomad planets then would have formed in smaller accretion disks without the required matter to form a star. If the paper is anything to go by this happens extremely often, to the tune of 100,000 times more often than there are stars in our galaxy.
Such planets are incredibly difficult to detect as we have no beacon to observe for wobbles (the radial velocity method). The only way we have to detect them currently is via microlensing and that means that the planet has to pass between us and another star for us to be able to see it. Even with so many planets and stars out there the chances of them all lining up are pretty slim which explains why we haven’t detected any to date. What we have found though are Brown Dwarfs and they’re quite interesting yet again.
Brown Dwarfs are what you’d call failed stars (or over-achieving planets, take your pick) as whilst they’re quite massive, on the order of 13 times the size of Jupiter at minimum, they still don’t have enough mass to ignite and become a fully fledged star. They do however generate quite a bit of heat which they give off as infra-red light. We can detect this quite readily and have identified many of them in the past. What’s intriguing though is that these Brown Dwarfs (or other nomad planets) could be used as stepping stones to the rest of the galaxy.
There’s a couple things that such planets could be used for. We already know that such planets could be used as a gravity slingshot to give current interstellar craft a speed boost en route to their destination. Another highly theoretical use would be to use these planets as refuelling stops if you were using some kind of hydrogen/helium powered craft. Such planets would also make excellent observation posts as they’d be far away from strong sources of light and radio waves, allowing them an extremely clear view of the universe. Indeed nomad planets could be quite the boon for an interstellar civilization, all we need is the technology to access them.
I’m very interested to see where this theory takes us and hopefully we’ll star seeing some nomad candidates popping up in the exoplanet catalogues in the next couple years. We might not yet be able to make use of them but their mere existence would tell us so much about the formation of heavenly bodies in our universe. At the same time it also raises a lot of questions that we haven’t considered before, but that’s the beauty of science.
Ever since we first discovered a planet outside our solar system way back in 1988 the hunt has been on to find another planet like our own. That’s not a particularly easy quest however as the methods that we currently have at our disposal, namely the radial velocity method (looking for little wiggles in the parent star) and the transit method (dimming of the parent star from our point of view) are heavily skewed towards finding large planets close to their parent stars. Finding a planet like ours by these methods not only requires precision tools but also great lengths of time, on the order of 2 years or so to ensure that what we saw wasn’t a fluke. Thus a planet like our own has escaped our detection because we’re simply unable to detect it.
The start of this year saw some major progress with the data from NASA’s Kepler mission. Back in January I blogged about Kepler-10b which is the smallest exoplanet that had been discovered to date. Unfortunately for planet hopefuls (and the planet as well) Kepler-10b was found no where near the habitable zone of its parent start. In fact the planet orbits its star in just under a day, putting its orbital distance at around 1/20th of the distance between mercury and our sun. The surface temperature there is enough to melt iron, eliminating the possibility for any kind of life as we know it to arise there.
However the astronomers working on the Kepler data didn’t just stop there as there. Within the wealth of Kepler data are some 48 other earth-like candidates, planets with orbital periods that places them squarely in the habitable zone of their parent stars. One of those potential candidates was Kepler-22b, a planet who’s orbit is much closer in than earth to its parent star which is a lot dimmer than our own. This mean that it was just on the edge of the habitable zone and the last piece of the puzzle was how big it was compared to earth. That last piece of the puzzle was just revealed today and Kepler-22b’s radius is 2.4 times the size of earth.
Whilst that makes Kepler-22b sound like some kind of giant it’s still within the boundaries of what we currently believe to be hospitable to life. The real kicker for Kepler-22b will be finding out its mass as currently, whilst we suspect that it’s rocky like our planet due to its position, we have no idea what its actually comprised of. Right now it could be anything from a planet covered entirely in oceans to a giant rock ball with little to no atmosphere. We can find out the mass by using the radial velocity method and I’m sure that’s the next step that NASA is taking in attempting to figure out just what kind of planet Kepler-22b is.
This might be the first exoplanet to be confirmed as being within the habitable zone but what’s more exciting is the prospect that we have another 48 candidates just waiting for their confirmations to come through. What we can infer from this is that our solar system’s composition isn’t unique and that the formation of terrestrial planets like our own is quite common. That means the conditions that brought about life on our planet are also common in other solar systems which leads to the tantalizing prospect that there’s other life out there just waiting for us to discover it. Of course it will be a long time before we manage to get there and see it for ourselves but it’s still incredibly exciting and I can’t wait to see what other kinds of planets we dredge up from the next 48 potentials.
Humanity, for the longest time, has been aware of planets outside the one that we reside on. Ask anyone today about the planets in our solar system and they’re sure to be able to name at least one other planet but ask them about any outside our solar system and you’re sure to draw a blank look. That’s not their fault however as the discovery of planets outside our solar system (which is by definition, not a planet but an exoplanet) is only recent, dating just over 20 years when the first was discovered in 1988. Since then we’ve discovered well over 500 more planets that exist outside our immediate vicinity and whilst their discovery is great none of them have yet been much like the one we currently call home.
In fact the vast majority of the exoplanets that have been discovered have been massive gas giants orbiting their parent stars at the same distance as Mercury orbits from our sun. This threw scientists initially as back then our current theories on solar system formation didn’t support the notion of large planets forming that close to their parent star. However as time we found more and more examples of such planets, these hot gas giants orbiting at velocities the likes we’d never seen before. The reason behind this is simple, the methods we use to find exoplanets are quite adept at finding these planets and not so much those which we’d consider potential homes.
The method by which the vast majority of exoplanets have been discovered is called the Radial Velocity method. As a planet orbits around its parent star the parent star also moves in tandem, tracing out an elliptical path that’s pinned around the common centre of mass between the two heavenly bodies. As the star does this we can observe changes in the star’s radial velocity, the speed at which the star is moving towards or away from this. Using this data we can then infer the minimum mass, distance and speed required to induce such changes in the planet’s radial velocity which will be the exoplanet itself. This method is prone to finding large planets orbiting close to their parent stars because they will cause larger perturbations in the star’s radial orbit more frequently, allowing us to detect them far more easily.
More recently one of the most productive methods of detecting an exoplanet is the Transit method. This method works by continuously measuring a star’s brightness over a long period of time. When an exoplanet crosses in front of its parent relative to us the star’s apparent brightness drops for the time it is in transit. This of course means that this method is limited to detecting planets and stars whose orbits line up in such a way to cause a transit like this. For earth like exoplanets there’s only a 0.47% chance that such planets will line up just right so we can observe them but thankfully this method can be done on tens of thousands of stars at once, ensuring that we discover at least a few in our search. Exoplanets discovered this way usually require verification by another method before they’re confirmed since there are many things that can cause a dip in a star’s apparent brightness.
There are of course numerous other methods to discover planets outside our solar system but for the most part the vast majority of them have been discovered by one of the two methods mentioned above. For both of them they are heavily skewed towards discovering big planets with short transit times as these produce the most observable effects on their parent stars. Still this does not preclude them from finding exoplanets like earth as shown with the recent discovery of Kepler10-b, a small rocky world in torturous conditions:
The planet, called Kepler-10b, is also the first rocky alien planet to be confirmed by NASA’s Kepler mission using data collected between May 2009 and early January 2010. But, while Kepler-10b is a rocky world, it is not located in the so-called habitable zone – a region in a planetary system where liquid water can potentially exist on the planet’s surface.
“Kepler-10b is the smallest exoplanet discovered to date, and the first unquestionably rocky planet orbiting a star outside our solar system,” said Natalie Batalha, Kepler’s deputy science team leader at NASA’s Ames Research Center in Moffett Field, Calif., at a press conference here at the 217th American Astronomy Society meeting.
Kepler-10b is the smallest transitioning planet to be confirmed to date and shows that it’s possible to discover worlds like our own using current technology. As time goes on and the amount of data increases I’m certain that we’ll eventually find more planets like these, hopefully a bit further out so they’ll be in the habitable zone. The Kepler mission is just a few months shy of its 2 year anniversary with at least another 1.5 years to go and if all goes well it should be returning swaths of data for us for the entire time to come.
I’m always fascinated by the latest discoveries in space even when they’re something like a molten mercury 564 light years away. Our technology is becoming more advanced with every passing day and I know that future missions will end up discovering millions of planets at a time with thousands of potentially life supporting worlds. It’s amazing to think that just 3 decades ago we couldn’t be sure that planets existed outside our solar system and today we know for sure there are more than 500 of them out there.
Ain’t science grand?
Staring up at the night sky is one of the most humbling experiences I’ve ever felt. Each of those tiny points of light is a sun burning furiously in a runaway fusion reaction. By comparison I, a mere human, am no more than a tiny fleck in comparison to one of those stars and barely even an atom when compared to the teaming masses of stars that make up that beautiful nightscape. Even more daunting then is the possibility that each of those twinkling stars plays host to a solar system like our own with dozens of planets just waiting for discovery. Our hunt for these planets has brought us hundreds of large gas giants who by the nature have been very easy to detect. Direct imaging of these planets has been nigh on impossible with the precious few we’ve managed to glimpse being extraordinary examples, rather than the rule. That is set to change, however.
Light, you see, is a funny thing. For centuries scientists pondered over the modelling of it, with the two dominant theories describing it as either as a particle or a wave phenomena. Problem is that light didn’t fit neatly into either of the models, requiring complex modelling in order to fit its behaviour into either the particle or wave category. Today many of the properties of light are now explained thanks to Einstein’s theory of wave-particle duality but for a long time one of the most confounding properties of light was that light can interfere with itself. You’ve probably seen this demonstrated to you back in college via the double slit experiment where you get a pattern of light and dark from a single source of light. At the time I didn’t think much of it past the initial intrigue but my discovery of my passion for space many years later had me thinking about how this might be used.
I had been reading about the hundreds of exoplanet discoveries for a while when I heard of 2M1207b which is thought to be the first directly imaged planet outside our solar system. It’s an exceptional planet being an extremely hot gas giant orbiting a very dim companion star. For systems like our own there would be no chance of seeing any planets from the outside thanks to our extremely bright sun and our relative proximity to it. Still knowing that light had the novel ability to cancel itself out I had wondered if we could say build an apparatus that forced light from a parent star to cancel itself out, letting us peer behind the blazing might to see what lie beneath.
It wasn’t until a few years later when I stumbled across the idea of a StarShade which had been proposed many years previously. In essence it would function as an augmentation to any space based telescope positioning itself perfectly in front of the parent star and reducing its brightness by a whopping 10 billion times. In comparison then the tiny planets which were once outshone would glow bright enough for the telescopes to be able to see them directly, hopefully leading to direct detection of many planets orbiting the star. Unfortunately it appears that this project is now defunct but that doesn’t mean the idea doesn’t live on in other forms.
Most recently an international collaboration of scientists developed a Apodizing Phase Plate coronagraph which is in essence a scaled down version of a starshade that can be installed in current telescopes:
Installed on the European Southern Observatory’s Very Large Telescope, or VLT, atop Paranal Mountain in Chile, the new technology enabled an international team of astronomers to confirm the existence and orbital movement of Beta Pictoris b, a planet about seven to 10 times the mass of Jupiter, around its parent star, Beta Pictoris, 63 light years away.
At the core of the system is a small piece of glass with a highly complex pattern inscribed into its surface. Called an Apodizing Phase Plate, or APP, the device blocks out the starlight in a very defined way, allowing planets to show up in the image whose signals were previously drowned out by the star’s glare.
It’s not just planets that this device helps discover either, it can also help detect distant objects that are hidden behind brighter ones. This enables telescopes to become even more powerful than they once were with minimal modifications. Probably the best part about this is that they’re already using them on the Very Large Telescope in Chile, proving that technology is much more than just a theory.
There’s so much to discover in our universe and it always gets me excited to see these pieces of technology that allow us to pull back the veil and peer ever further into the deepest parts of space. It’s so humbling to know that you’re just a tiny piece of a seemingly infinite universe yet it’s so enthralling that I lose myself for hours just staring up at the night sky. I feel so privileged to be living in a time were our knowledge of this universe is increasing at an ever accelerating rate yet we’re still left wondering at the awesome beauty that’s put before us.
For all the exploration of space we’ve done to date we have still found no evidence of life outside our own biosphere. We’ve found many of the building blocks scattered around our solar system but all our attempts to find even the most simplistic of life forms have been met with failure. Still with the raw ingredients being so common in just our own back yard it follows that there’s a high likelihood that somewhere in the deep blackness of space lies another planet that teams with life like our own. Still with the number of exoplanets only numbering in the hundreds and the technology strongly skewed to finding large gas giants close to their parent stars we had yet to come across another planet that life as we know it could call home. That was until just recently.
An enticing new extrasolar planet found using the Keck Observatory in Hawaii is just three times the mass of Earth and it orbits the parent star squarely in the middle of the star’s “Goldilocks zone,” a potential habitable region where liquid water could exist on the planet‘s surface. If confirmed, this would be the most Earth-like exoplanet yet discovered and the first strong case for a potentially habitable one. The discoverers also say this finding could mean our galaxy may be teeming with prospective habitable planets.
“Our findings offer a very compelling case for a potentially habitable planet,” said Steven Vogt from UC Santa Cruz. “The fact that we were able to detect this planet so quickly and so nearby tells us that planets like this must be really common.”
Vogt and his team from the Lick-Carnegie Exoplanet Survey actually found two new planets around the heavily studied red dwarf star Gliese 581, where planets have been found previously. Now with six known planets, Gliese 581 hosts a planetary system most similar to our own. It is located 20 light years away from Earth in the constellation Libra.
Gliese 581 is one of the most studied stars in our sky with no less than 6 exoplanets being discovered orbiting it. It’s a red dwarf star meaning it’s much less bright than our sun and is quite a bit less massive. Still the planets that are orbiting it look very familiar with one of it’s planets being very much like Venus (very close to the sun, probably a planetary hot house) and another quite like Mars (much further out, could potentially have or hosted life). The Gliese 581 system provides evidence that our kind of solar system, one with a diverse range of planets and several habitable candidates, is quite possibly very common. Gliese 581g is exciting because unlike it’s two sister planets it’s right smack bang in the middle of the habitable zone, and with that comes the chance of life.
In this picture Gliese 581 resides right near the bottom with the habitable zone being quite close to the parent star, right up to a mere 10% of the distance from earth to our star. Gliese 581g lies right in the middle of this zone and due to the close proximity this leads to a few interesting characteristics. A year on Gliese 581g is a little over 36 days long which is amazing when you consider Mercury, the closest planet to our star, still takes around 88 days to complete one rotation around our sun. Because of this close proximity to its parent Gliese 581g is also tidally locked to it, forcing the same side of the planet to always face the red dwarf star. Because of this I do not believe that life as we know it could exist on this planet. However that does not mean life could not survive (or even thrive) there.
Our version of life is the only model we’ve got to go on right now since we really haven’t come across anything different. Whilst many forms of life might look completely alien to us they all shared the same basics that enabled other life to thrive on earth. The key to all life as we know it is water as nearly everywhere on earth where there’s some form of water we tend to find life teaming there, even in the most inhospitable conditions. Gliese 581g is big enough that it should be able to hold onto a tenable atmosphere and the temperatures at the surface should be sufficient to support liquid water. However the weather on the surface would be anything but calm as cold wind from the night side of the planet would be constantly blowing thanks to the constant heating of the day side. The terminus boundary between eternal night and day could serve as a habitable strip all across the entire planet, but this is where things get tricky.
The day/night and seasonal cycles of this planet have greatly influenced how life formed on this planet. Gliese 581g would have none of these things with no orbital tilt to speak of to generate the seasons and either constant day or night depending on which side of the planet you were on. This means that any life that evolved there would have to cope with such conditions, eliminating the need for a circadian rhythm and any kind of seasonal behaviour. Since nearly all species of life on earth rely on both these mechanisms for survival the life on Gliese 581g would be wildly different from our own, probably lacking the need for sleep and being almost constantly active. Of course there would be other selection pressures at work here as well, leading to even more alien forms of life.
Is life guaranteed to exist there as so many articles claim? Not in the slightest. There are so many factors that lead up to the development of life that we just can’t be certain one way or another. There are some theories that the Moon played a large part in kick starting life on earth and right now we can’t tell if Gliese 581g even has one. There’s also the real possibility that our new celestial cousin has a thick, acidic atmosphere killing any early stages of life well before they had the chance to adapt. Until we can get more data on the planet anything we say about life there is purely speculative and really it will always be that way until we send a probe there to investigate.
Still Gliese 581g means so much to us for what it symbolises. It shows us that our solar system isn’t unique in the galaxy and gives evidence to support the idea that there are untold numbers of planets that are potentially habitable. We’re on the brink on discovering many, many more of planets like Gliese 581g and each one will give us some insight into the formation of our universe and ultimately life itself. We’re still a long way from being able to explore them for ourselves but I know that one day we mere humans will journey to those stars and revel in their beauty.
Whilst the vastness of space can not be underestimated, as I wrote about yesterday, there is still a lot for us to see out there. If we are to take a blind stab in the dark as to how many stars there are out there we end up with numbers in the ranges of 1024 or 1 000 000 000 000 000 000 000 000 (1 septillion) give or take a few hundred billion. Now consider how many of those stars would have planets or solar systems around them. This is where we start to imagine what that big number means for life in the universe.
Before we delve into the wonderful world of potential alien species I want to take you back to 1992. Before this day we could only speculate about solar systems outside our own. For us it would appear obvious that other stars out there had planet systems like our own considering the sheer number of potential stars out there. Even if the chance of generating a system like ours was a 1 in 1 trillion chance there would still be a million of them around. However we’d never actually proved that there were any planets outside our solar system, that was until Aleksander Wolszczan and Dale Frail discovered PSR B1257+12B (romantic I know) the first ever planet to be detected outside our solar system. It was a brilliant discovery at the time as up until then claiming the discovery of a planet was at the very edge of our capability. Several years later with improvements in technology and detection methods many more were discovered, with 358 being totalled to date.
Out of these 74 of them belong to multiple star systems, or approximately 20% of the observations so far. It’s a long stretch to say that 20% of all stars are hosts to multiple planet systems but we could assume 50% (to be generous) or greater are capable of hosting 1 or more planets. This leaves us with approximately 1 trillion potential candidates for planet formation in the universe with 20% of those having multiple chances. If this is sounding familiar to you then you already know I’m describing the drake equation, which attempts to predict the number of civilisations that we might be able to make contact with. So far the most common result of that equation is around 10, meaning just within our own galaxy there are 10 other species we would be capable of making contact with. Slight tweaks of the variables either way swing it wildly, and shows just how little we know for certain when it comes to estimating things like this.
The other side of this is the Fermi paradox which stipulates that despite the evidence to the contrary we haven’t actually managed to find signs of life through either contact or observation. Even our current list of exoplanets doesn’t have one on it that would be capable of supporting life as we know it (although that’s due to selection bias of the methods more than anything else). As the old saying goes absence of evidence is not evidence of absence, so we’re stuck at this point until we find some new data that points us in the right direction.
More interestingly is the potential for life within our own solar system. Take a look at Mars and Venus, two very similar planets to Earth that have very different fates. Mars on the one hand was too small to hold onto whatever atmosphere it had at the beginning and the lack of a magnetic field left it to fall prey to the solar winds. However studies have shown that Mars was once home to vast oceans and as such would have had most of the ingredients for supporting life. Since we haven’t found any signs of life yet it’s possible that there was something missing, and as such life never progressed. It is also possible that life died out as the planet’s protective barriers were withered away, but we’ll need to find something like a fossil before that’s even a possible past for Mars.
Venus on the other hand is something of a warning as to what can happen to a planet when it suffers from a runaway greenhouse effect. As far as we can tell Venus was very similar to Earth when they both first formed however strong volcanic activity has turned the planet into a hothouse, smothering it in clouds of sulphur and carbon dioxide. This has lead to a surface temperature above 400 degrees putting the chances of life there squarely at 0. This effect also stops us from making extended observations on Venus, so the possibility of it supporting life in the past is hard even to estimate. Curiously as well Venus has what we call a retrograde rotation, meaning that it spins in the opposite direction to every other planet in the solar system. As to why this happened we’re still not sure (and it seems the astrology cranks love harping on about it) although the best guess seems to be a combination of tidal locking forces and solar heating of Venus’ atmosphere.
Taking all of this into consideration you really get a feel for how unique and fragile life is. However, as our planet has shown, the conditions are right millions of different forms of life can prosper. I can not wait for the day when we discover another planet capable of supporting life and I hope that it’s not too far away.