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 Proxima Centauri Planet in Habitable Zone

August 31, 2016

Proxima Centauri, at 4.22 light years, the nearest star to the sun,  has planet 1.3 times the mass of the Earth with a temperature suitable for liquid water on its surface. Discovered by the radial velocity method, Proxima b orbits its red dwarf star every 11.2 days. There is no evidence that Proxima b transits across the disc of its parent star. The discovery was confirmed during the first half of 2016 when Proxima Centauri was regularly observed with the HARPS spectrograph on the ESO 3.6-metre telescope at La Silla in Chile while its brightness was simultaneously monitored by other telescopes around the world. Careful analysis of radial velocities of the star revealed a planet with a mass at least 1.3 times that of the Earth, orbiting about 7 million kilometers from Proxima Centauri — about 5% of the Earth-Sun distance. The presence of another super-Earth mass planet at longer orbital periods cannot yet be ruled out.

Presence of a Proxima Centauri planet has been reported during past years, but active flaring of a red dwarf can give a false indication of a planet. To rule this out, the changing brightness of the star was monitored with the ASH2 telescope at the San Pedro de Atacama Celestial Explorations Observatory in Chile and the Las Cumbres Observatory telescope network around the world. Radial velocity data taken when the star was flaring were excluded from the final analysis, which was based on a detailed understanding of how the brightness of the star changes on timescales from minutes to a decade,

The team of astronomers was led by Guillem Anglada-Escudé, from Queen Mary College, University of London, who is the lead author of a paper describing the discovery in Nature. Besides data from the recent campaign, the paper incorporates contributions from scientists who have been observing Proxima Centauri for many years. These include Martin Kürster and Michael Endl of the UVES/ESO M-dwarf program, and exoplanet search pioneers such as R. Paul Butler. Public observations from the HARPS/Geneva team obtained over many years were also included.

Although Proxima b orbits much closer to its star than Mercury does to the Sun, the star (α Centauri C) has 10 per cent of the sun's luminosity,14 per cent of its diameter, 12 per cent of its  mass, and about 52 per cent of the sun's effective temperature. As a result Proxima b lies well within the habitable zone around the star and has an estimated surface temperature that would allow the presence of liquid water. Despite the temperate orbit of Proxima b, the conditions on the surface may be strongly affected by the ultraviolet and X-ray flares from the star —  more intense than the Earth experiences from the Sun. (More. . .)