With the trillions of stars that exist in the universe (not to mention the possibility of multiple universes), many of which have planets orbiting around them, it seems highly improbable that Earth is the only planet habitable for life. The question for me is, therefore, not so much is there life on other planets, but rather, is it possible to ever discover this life? And then the most intriguing question of all, what could this life be like?
Astronomers took the first step to answer this question 15 years ago when the first planet outside of our solar system was discovered. In March of 2009, the Kepler mission sent a spacecraft out in search of habitable planets and planetary systems. It found the first approximately Earth-sized candidate 2000 light years away in August of this year, but by then had found 700 planets overall. Around the same time, a European team found an even smaller planet only 127 light years away that is closer to the size of Earth.
But does this mean there is potential for life on these planets? It's highly unlikely. They are too close to the sun--they are likely too hot and their orbits are very short. However, it gets me thinking...how much does another planet need to be habitable in the sense ours is? and to what extent can life be different from ours? What if the very building blocks of life were different? Is this possible? Or is it really that lucky that Earth just happened to get everything perfectly right? These are questions to be addressed later on.
For now, another interesting part of this article is how exactly astronomers go about looking for planets. One way is by spotting when a planet passes in front of a star, thereby dimming it slightly. From this scientists can figure out how big it is. And this is just what the Kepler mission is doing by focusing on an area of the night sky and looking for changes in the luminesence of stars. Scientists can also pick out planets based on the pull of their orbits on the star in their solar system.
However, even when the Kepler mission does find a planet, it cannot tell what the atmosphere is like. It can tell the approximate diameter, mass, and distance from the star but this is just a first step in discovering if there is the possibility of life there.
It truly is amazing to consider how far space technology has come over the past years and yet how far it has to come to ever find out if life actually does exist on another planet. Is it ever conceivable to be able to see that life? Judging just by the distance between us and other planets, it would take so long to get there or to pass a signal there, that whoever sent out a message would not be alive to get the result. Not to mention that the possible habitability of another planet as we see it today, is not the exact state of the planet itself today, since looking out into space is looking back into time.
Hi Kelsey,
ReplyDeleteThanks for the post. One thing I'd like you to think about is the interrelated nature of the various techniques for finding extrasolar planets. For example the transit technique you describe (and which Kepler relies on), is extremely useful in measuring the size of planets. The radial velocity technique (which was used to detect the first extrasolar planets) is very good for detecting the mass of the planets. However, when combined, the two techniques can tell you the density of the planet, and therefore its probable composition. Of course, the transit technique has its limits, too--most planetary systems won't be found this way at all, because the planets orbit in such a way that they never transit as seen from Earth.
It turns out that astronomers are also starting to figure out how to get at the atmospheric composition--in the past few years, we've actually detected the atmospheric absorption from a few giant planets around other stars (by subtracting the spectrum of the star when the planet is behind the star from the spectrum of the planet+star). Getting the spectrum of the atmosphere of the earthlike planets will be much harder, but that's what future missions like the Terrestrial Planet Finder are designed around. Ultimately, progress on this front is happening so fast that I'm optimistic that the relevant question is "when?" rather than "if?".
A final, minor, point--although it's true that telescopes are time machines and looking into space is looking back in time, the stars we're finding planets around are close--within a few hundred light-years. It's really unlikely that the habitability of a planet would change so much in such a short time.
Ian