The planet, Barnard's Star b, is about as far away from its star as Mercury is from the Sun. It's the second closest exoplanet to Earth after Proxima Centauri b, whose discovery was announced in 2016.
Barnard's Star is an extremely dim object known as a "red dwarf"; it's about 3% as bright as the Sun, so it emits far less solar energy.
The planet orbits beyond a boundary called the "snow line", which is past the traditional habitable zone, where water can remain liquid on the surface.
On distance alone, it's estimated that temperatures would be about -150C on the planet's surface. However, a massive atmosphere could potentially warm the planet, making conditions more hospitable to life.