Extrasolar Planets

The formation of planets in the process of star formation appears now to be commonplace. Ward and Brownlee in their book Rare Earth make the point that the formation of a planet like Earth that can support advanced life may be exceedingly rare. The search for and characterization of extrasolar planets is currently a very active area of research.

At present, it appears that the closest star with a planet is Epsilon Eridani, a relatively yound orange-red dwarf star only 10.5 light years from the Earth. The planet is about 1.5 times as massive as Jupiter and is in a highly elliptical orbit swinging from 2.4 to 5.8 Astronomical Units from the star compared to Jupiter's nearly circular orbit at 5.2 AU.

Another close neighbor, Barnard's Star, has also been shown to have planets. A protoplanetary disc around Vega has been studied. According to Ward and Brownlee, the count of extrasolar planets was 198 in 2000, with the count now having exceeded 200.