Alpha Centauri Bb

Alpha Centauri Bb (α Cen B b) was a proposed exoplanet orbiting the K-type main-sequence star Alpha Centauri B, located 4.37 light-years from Earth in the southern constellation of Centaurus. Its existence was announced in October 2012 by a team of European observers, and the finding received widespread media attention. However, the announcement was met with scepticism by some astronomers, who thought that the European team was over-interpreting its data.

In October 2015, astronomers from the University of Oxford published a scientific paper disproving the existence of the planet. They observed that an identical statistical analysis of randomly-generated synthetic data gave the same results as the actual astronomical data. This led Xavier Dumusque, the lead author of the original paper, to concede "We are not 100 percent sure, but probably the planet is not there."

Starting in February 2008, and continuing through July 2011, a team of European astronomers, mainly from the Observatory of Geneva and from the Centre for Astrophysics of the University of Porto, recorded measurements of Alpha Centauri B's radial velocity with European Southern Observatory's HARPS echelle spectrograph at the La Silla Observatory in Chile. The team made 459 observations of Alpha Centauri B's color spectrum over a four-year period, then used statistical filters to remove known sources of variance.

On 16 October 2012, the team announced they had detected an Earth-mass planet in orbit around Alpha Centauri B. The discovery was presented in the scientific journal Nature, with lead author Xavier Dumusque, a graduate student at the University of Porto. He called their findings "a major step towards the detection of a twin Earth in the immediate vicinity of the Sun".

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