Astronomers are very interested in detecting planets orbitting other stars. However, it is not possible to directly observe fully-formed planets since they are <1> their parent star. It is possible to detect dusty disks of material surrounding stars from which planets may eventually form. These disks are known as protoplanetary disks are typically detected in <2> light. The first such system was detected by IRAS in 1983 and is known as <3>. Astronomers look for assymetries and radio hot spots in these disks as evidence of planets in formation.
To detect fully formed planets, astronomers look for indirect evidence of their extistence from the effects they have on their parent star. Over 100 extrasolar planets are known to exist today from the radial velocity technique. This technique detects periodic fluctuations in the radial velocity of a star from doppler shifts in its spectral lines caused by movement around the star-planet center of mass. When the planet is moving away from us, the star moves toward us and its spectral lines are <4>. While when the planet is moving toward us, the star moves away from us and its spectral lines are <5>. Radial velocities for the star at a number of different times are calculated from the doppler shifts of these spectral lines. The time interval between maxima in the star's radial velocity is equal to the <6>. The mass of the planet is calculated from the maximum value of radial velocity. However, this mass value is a <7> for the planet's mass since we don't know the inclination of the system relative to our line of sight.
Astronomers expected to find planets similar in characteristics to those in our own solar system. They were surprised to discover <8> mass stars in <9> <10> orbits. The most likely explanation of this is that large Jovian planets move after formation into new orbits.
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