In 1963 Peter van de Kamp made an announcement based on his studies, that Barnard's star, which is a small red star located about six light years away had an unseen companion.
Six years later, he made a correction of his previous announcement and stated that Barnard's star actually had two companions, one which was 0.7 times as massive as Jupiter and the other only half as massive as Jupiter. Other scientists failed to verify this discovery. Not even studies made by the Hubble telescope have been able to find any planet around that star.
However, the real discovery of an extrasolar planet around a sunlike star came in 1995 when the first extra solar planet was discovered orbiting around another star: 51 Pegasi. The planet was named Bellerophon and was discovered by a Swiss team, lead by Didier Queloz (the swiss team beat their american rivals, lead by Jeff Marcy and Paul Butler). It was measured to have 0.6 times the mass of jupiter, which makes it a gas giant,
but it orbited its star in only 4 days! The information gathered told us that it is a very hot world, with the estimated temperature of around 1 300 degrees Kelvin. Its so hot that metals exist as vapour in the atmosphere!
Though, how does this (and other) gas giant fit into astronomers' theories of how planets are formed?
During the creation of a solar system lighter elements such as hydrogen and helium are blown towards the edges of the system (because the heat from the sun provides the gas high kinetic energy) while heavier elements stay relatively close to the star.
This theory matches our solar system since there are first four rocky elements and then several hundred million kilometres away are the gas giants.
The theory does not explain why the planet 51 Pegasi B and other gas giants orbit very close to their stars.
In fact, some astronomers now believe that the gas giants were created further away and the gradually migrated close to their stars in a spiral orbit, ending up in close, tight orbit.
According to the theory it is very difficult for small rocky planets to exist in an orbit closer to the star than the gas giant's original orbit, like they do in our solar system, because the protoplanets would have been bulldozed by the gas giants that are migrating inwards.
For this reason, astronomers look for solar systems that have gas giants orbiting in a stable, circular orbit when searching for planets the size of earth.
In any case, directly or indirectly, the search for extrasolar planets or exoplanets as they are sometimes called, is a search for mankind to find out if we really are alone in this vast universe. Today, more than 400 planets have been discovered to orbit other stars, most of which are hot jupiters. The search is narrowing down to look for smaller and more earthlike planets. NASA is planning on launching a new spaceprobe, Kepler to search for habitable planets in our neighbourhood of the Milky Way Galaxy.
How To Detect Extrasolar Planets