Okay, strictly speaking it’s a maybe-habitable planet. But still!
Yesterday the European Southern Observatory announced the discovery of an Earthlike planet orbiting the star Gliese 581. “Earthlike”, to astronomers, is a pretty broad definition; it means a planet that is not so tiny it will lose all its atmosphere to space, nor either so large that its surface will be crushed under hundreds of atmospheres of pressure; and not so cold as to be a frozen iceball, nor either boiling hot. Basically, it’s a planet that can support liquid water.
This is a broad definition, but up until now astronomers have found over 200 planets around other stars without finding a single one that fit. Most were too big — it’s much easier to detect giant planets than little ones, of course — and the ones that weren’t, were either too hot or too cold.
But the new planet — which goes by the euphonious name of Gliese 581c — is a “Goldilocks” world, just right. It orbits Gliese 581c in the “habitable zone”, receiving just about as much sunlight as earth.
Of course, there are some complications.
First, Gliese 581c is a red dwarf, a star much smaller and dimmer than our sun. So, the planet has to be much closer. In fact, it’s so close that it orbits the star every 13 days or so.
Second, because it orbits so close, it’s probably “tidally locked”, with one face always facing towards the star and one always facing away. This could mean the day-side is a burning desert, while the night-side is a frozen wasteland. On the other hand, computer simulations suggest that circulation of oceans and atmosphere could move enough heat around to moderate the temperatures. We still don’t know for sure.
Third, it’s a bigger world than Earth, about five times as massive. The surface gravity would be about 1.6 times ours. So, if you weigh 80 kilos, you’d weigh about 130 there.
Fourth, it’s 20.1 light years away. By galactic standards, that’s just down the street; Gliese 481 is considered a close neighbor. But it’s still so far that a beam of light takes more than 20 years to reach it. The fastest space probe we’ve ever built would take something like 30,000 years to get there. We are at least a century away from building something that could travel there, and it’s quite possible that we never will.
Nevertheless, we now know that Earth is not unique. In fact, finding a roughly Earthlike planet so close (by galactic standards) suggests that they may be pretty common. It’s a big deal.
And we have a bunch of Europeans to thank for it. The European Southern Observatory is an international organization for observational astrophysics. It is supported by twelve member states, all Europeans. It operates several telescopes in Chile. (Because you can see different stars from that far south, and also because the Atacama desert is great for astronomy — very high, with thin, dry air and no weather.) It’s based in a suburb of Munich.
I could go on about this for some length — how they found it (tiny wobbles in the movement of the star), who else was looking, what the prospects are for more similar discoveries — but leave that be. Key point: it’s one of the coolest scientific discoveries of the century so far, and it reshapes the way we think about the universe.
So, kudos to the European Southern Observatory.