An open system is more conducive to life than TRAPPIST-1 because star is a red dwarf, and similar to the Sun, according to arXiv.
The masses of the planets found reach of 1.7 Earth masses, making them among the smallest of the heavenly bodies, found near sun-like stars. To detect them it took delicate equipment, which is able to register small values of the radial velocity of the star (up to 30 centimeters per second). Registration of such weak signals is made possible thanks to the introduction of new technologies, allowing to get rid of the noise in the data.
All four sites are rocky, however, only two planets, the most distant Tau Ceti, potentially suitable for life. At the same time, they are likely exposed to a constant bombardment by comets and asteroids as a star surrounded by a disk of solid debris.
In 2016, astronomers announced that they have found a system of TRAPPIST-1, which contains three exoplanets. They revolve around a red dwarf, distance from the Earth at a distance of 39 light years. While local star be a powerful emission of plasma.