Extrasolar Planets



"An extrasolar planet, or exoplanet, is a planet which orbits a star other than the Sun, and therefore belongs to a planetary system other than the solar system. As of August 2006, over 200 extrasolar planets have been discovered"


Image: Some stars known to have at least one orbiting planet.


For centuries, extrasolar planets were a subject of speculation. Astronomers generally supposed that some existed, but it was a mystery how common they were and how similar they were to the planets of our own solar system. The first confirmed detections were finally made in the 1990s. Since 2002, more than twenty have been discovered every year. It is now estimated that at least 10% of sunlike stars have planets, and the true fraction may be much higher. The discovery of extrasolar planets raises the question of whether some might support extraterrestrial life.



Planets Observed

Observational Selection

Due to the current detection methods employed, the vast majority of exoplanets found so far have:


It appears plausible that in most exoplanetary systems around sunlike stars, the largest planets are comparable in size to Jupiter or Saturn. Also, the fact that astronomers have found several planets only a few times more massive than Earth, despite the great difficulty of detecting them, indicates that such planets are fairly common.

It also appears plausible that in most exoplanetary systems, there are one or two giant planets with orbits comparable in size to those of Jupiter and Saturn in our own Solar System.


General Observations