TRAPPIST-1, is an ultra-cool red dwarf star that is slightly larger but much more massive than the planet Jupiter, located 39.6 light-years from the Sun in the constellation Aquarius.
2017 was a big year concerning TRAPPIST-1, with the news that this star has a system of seven planets, and that three of which are Earth-sized in what is called a goldilocks orbit, which mean that they could have liquid water.
A fourth planet orbits the inner edge of the habitable zone.
On February 5, 2018, astronomers announced the results of two different studies, one observational and the other theoretical, but based on observations. The studies suggest the TRAPPIST-1 planets are what astronomers call terrestrial, meaning that they are more similar to the small rocky worlds Mercury, Venus, Earth and Mars than to gas giants Jupiter or Saturn. And they suggest these worlds are rich in volatile materials, probably water.
To sum it up, this means that some of these planets could possibly have close to Earth-like characteristics.
Sources:
https://en.wikipedia.org/wiki/TRAPPIST-1
http://www.eso.org/public/usa/images/eso1805b/
http://www.eso.org/public/usa/images/eso1615d/
