james_nicoll's sharing on Facebook of an astronomer's tweet announcing the discovery of "Alpha Centauri Bb", that is, a planet orbiting the slightly dimmer but still Sun-like orange dwarf star of Alpha Centauri B. Such a planet would be the nearest planet discovered--indeed, since Alpha Centauri's three stars are the closest stars to our own planetary system, it's likely to retain that title for some time.Nicoll also linked to a Croatian-language news article, ably translated by Google, that goes into more detail. Apparently Bb, while Earth-like in mass, orbits B just six million kilometres away, much closer than Mercury.
European astronomers have discovered that around the nearest star Alpha Centauri orbits the planet whose mass is nearly equal to the Earth
It is also the lightest planet ever discovered. Investigations were carried out with the help of the instrument HARPS mounted on the 3.6 m telescope of the La Silla Observatory in Chile.
[. . .]
'Our observations HARPS instrument that lasted for more than four years have revealed a small, but real signal coming from the planets turned around Alpha Centauri B every 3.2 days, "said lead researcher Xavier Dumusque from the Geneva Observatory and the Centro de Astrofisica da Universidade do Porto in Portugal. "This is an extraordinary discovery, in which we use our technique to the limit. '
The existence of a small planet was determined from the wobble of the star images influenced by its gravity. The effect is truly portable - runs the star forward or backward at a speed of 1.8 kilometers per hour, which is about the speed of crawling children. The planet is around Alpha Centauri B at a distance of about six million [kilometres], much closer than Mercury is to the Sun. From another star Alpha Centauri A is a hundred times further, however, and it is in his heaven, probably a very shiny object