In May of last year, astronomers from MIT and the University of Liège discovered a dwarf star they named TRAPPIST-1. The relatively cool star had three planets in its orbit, one of which was situated in just the right zone to meet the conditions for life. Well, it wasn’t just us who thought that was a pretty rad discovery — astronomers from a number of other institutions have started to look at TRAPPIST-1 more closely, leading to the discovery of not three, but seven (and possibly more) planets around the star.
While the planets are all described as having “sizes and masses similar to those of Earth” in an article published in Nature this week (alongside a NASA press conference), only three are good candidates for life according to the astronomers’ models. The three innermost planets, TRAPPIST-1b, 1c, and 1d, are thought to be close enough to the star to suffer from a runaway greenhouse gas effect, while the outermost 1f likely doesn’t get enough heat to sustain liquid water. But, 1e, 1f, and 1g are in the Goldilocks zone, meaning they could (not necessarily do) have oceans of liquid water.
Life would be quite a bit different on those planets. The TRAPPIST-1 system is much more closely bunched together than ours, meaning in part that other planets would appear much bigger in the sky, more like how the Moon appears on this one. Years on the planets only last from one to thirteen days, and all seven are thought to be tidally locked — permanent day on one side, permanent night on the other. The astronomers also discovered that rather than forming near the star, the planets moved in closer to the star over time.
The additional planets were discovered thanks to the use of the NASA’s Spitzer Space Telescope in September of last year. An object that astronomers originally thought belonged to one planet was recognized as four, as distinct orbits were detected by continuously monitoring TRAPPIST-1.
As always, further research is needed — for starters, there’s always a chance this planet-dense system could be hiding even more planets. Astronomers will also need to pin down the atmospheric compositions of these planets to see if they’re actually suitable for life. All that’s been inferred so far is the mass of the planets, their orbits, and how much heat they likely receive from the star, so there’s a long way to go yet.
Header image: NASA/JPL-Caltech