Well squee! NASA announced that the little star TRAPPIST-1 has 7 rocky planets, ranging in size from 40% to 140% of Earth’s mass. They’re all very close to the star, closer than Mercury is to our own Sun, but TRAPPIST-1 is an ultracool dwarf star, with a surface temperature of perhaps 2,500 ºC. Our sun is about 5,500 ºC. This means that several of the planets are in the Goldilocks zone – not too cold not too hot, just right. In fact, if they have the right atmospheres, they might all be the right temperature for liquid water on the surface. Since they’re only 39 light years away, we should be able to find out. (OK, 39 light years is 368,967,300,000 km, but the centre of our galaxy is 28,000 light years away.)
The discovery was very much a joint effort. The TRAPPIST telescope in Chile initially found that the star had planets, hence the name, TRAPPIST-1. TRAPPIST looks for the dip in light from a star as a planet passes directly in front of it, a technique pioneered by the SuperWASP telescope on La Palma. Initially, the Belgian astronomers thought there were just 3 planets, but that didn’t add up. So the Herschel and Liverpool telescopes on La Palma took a look, and eventually NASA set the Spitzer space telescope to look at the star for three solid weeks. That’s a pretty generous allocation of resources, and it produced enough data to clear up the mystery.
Those pretty pictures you can find on the web are artists impressions. We still don’t know what they look like, so watch this space. But these planets are really close to each other, so when they’re at their closest, they’ll be really big in each other’s skies. I don’t have nay numbers to crunch yet, but they won’t just be bright dots like Venus and Mars; they’ll look almost as big as our moon.
Here‘s the New Scientist article about the discovery.
And here’s the full NASA press conference.