After years of searching, an international team of astronomers says they’ve found definitive evidence of a planet orbiting Proxima Centauri, the closest star to the sun. The details are published in Nature today, and this is potentially the single most exciting exoplanet discovery to date.
The planet, named Proxima Centauri b (Proxima b for short), is probably slightly more massive than the Earth, and is about the right distance from Proxima that it could have liquid water on its surface.
Proxima Centauri is a faint red dwarf star, just 4.24 light years from Earth. Despite its proximity, the star is too faint to be seen with the naked eye, which leaves its neighbour, Alpha Centauri, as the closest star that can be seen without a telescope.
Proxima is almost certainly bound to Alpha Centauri, which is itself a binary star, moving with it through space in a stately celestial waltz.
Proxima has been the target of planet-search observations since the dawn of the exoplanet era. The new discovery used observations taken from the European Southern Observatory between 2000 and 2014, and an additional suite of data taken between January 19 and March 31 this year.
The technique used for the discovery is the Doppler wobble method, where observers measure the line-of-sight velocity of a star with exquisite precision, and watch for any evidence of the star rocking back and forth in space.
Introducing Proxima Centauri b
The evidence is strong that Proxima Centauri is host to at least one planet. The new world orbits the red dwarf star roughly every 11.2 days, at a distance of about seven million kilometres (far closer than Mercury orbits the sun).
Because the planet has been inferred from the line-of-sight wobble of its host, its mass remains uncertain, with the true value depending on the tilt of its orbit.