 Astronomers tell us that there are hundreds of billions of exoplanets in the Milky Way. Now with so many other planets orbiting other stars, the obvious question is, are any of them like Earth? Well, we don't really know the answer to that question. A promising place to start looking might be the Trappist-1 planetary system. It's a red dwarf star and has seven planets orbiting it. And back in early 2017, astronomers announced that three of those seven planets are in the habitable zone of that star. But it's not enough to just be in the habitable zone. Astronomers have been working in the year since that discovery to find the key ingredients that would actually make those planets habitable. That being an atmosphere, a temperate climate, and liquid water on the surface. Using combined data from NASA's Spitzer and Kepler space telescopes, astronomers have made precision measurements of the densities of these three planets. Now it's important to know the densities because if you know the density well, then you can make a guess as to what the planet is made of. And early results are showing that at least for one of the planets, 5% of its mass could be in liquid water form. And in comparison, Earth's oceans make up 0.2% of our mass. Astronomers also went looking for atmospheres on these three planets using the Hubble Space Telescope. Now Hubble wasn't designed to look for atmospheres. In fact, it was launched before exoplanets were even discovered. But using it, they were able to rule out big puffy atmospheres, ones like on Neptune or Uranus. And so if they do have atmospheres, they're compact, like Earth, Venus or Mars. With three rocky planets in the habitable zone, the potential for liquid water on the surface and the hunt still going for atmospheres, that makes Trappist one of the most interesting planetary systems that we know of. And it makes it one of the more likely candidates for the James Webb Space Telescope to go looking at after it's launched because JWST was specifically designed to go looking for exoplanet atmospheres. But since JWST isn't launching until 2019, it might be a couple more years before we get the answers that we want.