It used to be simple. We had 9 planets. 4 were small and rocky and close to the Sun. 4 were big and gassy and far from the Sun. The we had Pluto. The first disruption of this pretty picture was when we found of other bodies like a Pluto and so decided Pluto could not be a planet. Then we found other planetary systems in which the large planets were close to the star. Now the latest discovery might mean a complete rethink of our whole notion of planets. Now we have discovered a planet the same size as Earth, but gassy and not rocky.
Earth’s gassy ‘twin’ has been discovered in another solar system 200 light years away and is known as KOI-314c. It weighs the same as Earth but is 60% larger, leading scientists to suspect it has a thick gaseous atmosphere. It orbits a dim red dwarf star at such a close distance that temperatures on its surface could be as high as 104C – too hot for most forms of life on Earth.
Lead astronomer Dr David Kipping, from the Harvard-Smithsonian Centre for Astrophysics in the US, said: “This planet might have the same mass as Earth, but it is certainly not Earth-like. It proves that there is no clear dividing line between rocky worlds like Earth and fluffier planets like water worlds or gas giants.”
They’re also showcasing yet again that a major assumption astronomers were making as recently as 1995—that other solar systems would more or less resemble ours—was completely misguided. “Nature,” says Kipping, “continues to surprise us.” By now, that should hardly be a surprise.