Properties of the Exoplanets All the extrasolar planets discovered so far have three common characteristics: They are all giant planets, like Jupiter in our own solar system, much heavier and certainly not like Earth. They are located quite close to their central star. This also is why astronomers took so long to discover them and had to rely on indirect observing methods. The giant planets in our own Solar System are at much greater distances from the Sun than are these planets from their star. They are all in systems around stars relatively nearby, because that is where we can best search for planets with optical telescopes currently available on Earth. With better telescopes in the future, we will be able to explore more distant parts of the Universe and to look for smaller planets. The extrasolar planets discovered first revolve around the stars 51 Pegasi, 70 Virginis, 47 Ursa Majoris, 55 Cancer, Ypsilon Andromeda and Tau Bootis. All these stars are rather close to us., We can actually see 47 Ursa Majoris and 70 Virginis with the naked eye on a clear spring evening. The masses of these planets range from slightly less to many times more than Jupiter's mass. The most amazing factor is without doubt, the small distance from their central stars. In the case of 51 Peg, the companion is almost half the mass of Jupiter and is placed at only 0.05 astronomical units (about 7.5 million km) from its star, which is 100 times closer than Jupiter and 20 times closer than the Earth is to our Sun. The same applies to most of the other known extrasolar planets. In our solar system, the giant planets are placed in the outskirts and the terrestrial ones are closer to the Sun. So, this may mean that those exoplanets were formed farther out and then migrated inwards and came much closer to their star. One of the important questions, concerning whether other planetary systems exist with more than one planet around a star, was answered recently. We know now that Ypsilon Andromeda has three giant planets orbiting their central star at close distances, less than 2.5 AU (350 miiion km) away. This was the first planetary extrasolar system to have been discovered and as the observations continued and new discoveries were made, two more planetary systems were soon found. Who knows what the future will bring? On the basis of these discoveries of small planets around a pulsar and giant planets around foreign suns, it appears quite likely that our solar system does not represent the only possible type of planetary system, indeed it is probably not EVEN of the most common type.