NASA’s Kepler mission recently announced that they have come one step closer to finding an Earth-like world by identifying their first exoplanet which both orbits a star similar to our own Sun, and does so within the so-called “habitable zone”. This is pretty amazing, considering what it takes to see something as small as a planet from so far away. The Kepler space telescope keeps an unblinking eye on a region of our galaxy packed with hundreds of thousands of stars, and monitors every single one of them for the slightest dip in brightness. When these dips follow a certain pattern, it indicates that the star has a planet which has passed between it and us, and the timing of the dips can reveal the planet’s orbital distance and it’s diameter. But there is a limit to what this technique has been able to achieve so far, which is why only the largest, fastest moving planets have been seen so far. Even with these limitations, Kepler has upped the official count of possible explanets to over a thousand, and the number keeps climbing.
The fanfair around this most recent discovery is a little misleading though. The implication is that we have found another Earth, complete with liquid water and that is is buzzing with life. This is unfortunate, since I think that what they’ve actually achieved is pretty astonishing as it stands, without the need to exaggerate. The facts are as follows: A yellow G-class star, similar to our own Sun, has been found to have an “earth-like” planet, orbiting in the habitable zone. This means that the star has the same basic properties as our Sun – colour, temperature, size. The habitable zone is a range of possible orbits in which a planet could conceivably have liquid water, which is essential to all life on Earth. Anything outside this zone would either be cold enough that ice could never melt, or that steam could never condense. And by ‘Earth-like’, they mean that the only thing anybody knows about the planet is that it is some 2.4 times larger in diameter than the Earth. It might be made of rock, like Earth, or it could be composed of Gas (like the four largest planets in our own Solar System), or it could even be made from water and ice. The occultation technique used by Kepler cannot reveal these details.
That said, it is astonoshing that we’re able to detect planets at all. Less than 20 years ago, exoplanets were pure speculation, but in a short time we’ve gone from wondering “Do planets even exist outside the Solar System?” to assuming that most Stars have them. And that is a huge leap forward, even without having to invoke ET in every single press release.