  At a distance of 1.295 parsecs, the red-dwarf Proxima Centauri ($\alpha$
Centauri C, GL 551, HIP 70890, or simply Proxima) is the Sun's closest stellar
neighbor and one of the best studied low-mass stars. It has an effective
temperature of only $\sim$ 3050 K, a luminosity of $\sim$0.1 per cent solar, a
measured radius of 0.14 R$_\odot$ and a mass of about 12 per cent the mass of
the Sun. Although Proxima is considered a moderately active star, its rotation
period is $\sim$ 83 days, and its quiescent activity levels and X-ray
luminosity are comparable to the Sun's. New observations reveal the presence of
a small planet orbiting Proxima with a minimum mass of 1.3~Earth masses and an
orbital period of $\sim$11.2 days. Its orbital semi-major axis is $\sim0.05$
AU, with an equilibrium temperature in the range where water could be liquid on
its surface.
