Trappist-1

By almost any standard, Trappist-1 is an underachiever. The star is only about eight percent as heavy as the Sun. Any less massive and it wouldn’t be a star at all. And because of its tiny mass and size, it’s quite feeble — less than a tenth of a percent of the Sun’s brilliance.
In one way, though, Trappist-1 is an over-achiever. It has seven known planets — more than any star system other than our own. As befits a tiny star, though, it’s a tiny planetary system. There are no giant worlds, and all of the planets are within a few million miles of the star — just a fraction of the distance between the Sun and its closest planet, Mercury.
At least three of the planets appear to lie within the star’s “habitable zone.” That’s the distance from the star where temperatures are just right for liquid water, which is a key ingredient for life.
That doesn’t mean other conditions are right for life, though. In fact, a couple of studies released earlier this year suggest the planets probably ar