Scientists this week announced the discovery of a system with more than one planet. This is the second solar system discovered in about two years.
Kenneth Chang
Pictured: Simulation of the Upsilon Andromeda system
Astronomers announced this week that they have found evidence of the existence of a second multi-stellar system (a star and several planets around it). Until now, only one such system was known, apart from the solar system.
The astronomers, from the University of California at Berkeley, estimate that when a planet is discovered around a star, in most cases several other planets move around the star. The reason astronomers haven't discovered more multi-star systems, they say, is that they just haven't tried hard enough.
Astronomers first discovered a planet outside the solar system only five years ago. The total number of stars "carrying" planets has so far reached 40, including 10 "new" stars, which were announced at the meeting of the "International Astronomical Union", which opened yesterday in Manchester, England. As mentioned, more than one planet was discovered around only two of them.
Almost all the planets outside the solar system were discovered indirectly - the gravitational force that caused the mother star to move back and forth created a slight tremor in the light waves coming from the stars.
Dr. Debra Fisher of the University of Berkeley re-examined the data from 12 stars known to have planets around them. She asked to find out if there was any evidence of the presence of other planets in them. "Five of them showed signs of excessive shaking," she says, "and this indicates the presence of another factor." The invisible bodies may be additional planets, dark neighboring stars, or "brown dwarfs" (small stars that emit almost no radiation).
A year ago, the team of researchers from Berkeley announced that they had discovered three planets around the star Epsilon Andromeda, which is 44 light years from Earth. Astronomers led by Dr. Michael Maior from the Geneva Observatory, Switzerland, announced in May that they had discovered a planet around the star HD 83443, 141 light years from Earth, and at a conference in Manchester they were to announce that they had discovered another planet in orbit around HD 83443.
The new multi-star system surprises astronomers: the two planets are huge, have gases and are very close to the star. One of them, located at a distance of 5.6 million km from the star, orbits it in three days. The other orbits its star in 30 days. For comparison, Mercury, the innermost star in the solar system, is about 57 million km from the sun and orbits it in 88 days.
Compared to other planets discovered so far, the two stars orbiting HD 83443 are quite small; One is only slightly larger than the planet Saturn, and the other is half as small. The size of Saturn is a third of the size of Jupiter, most planets outside the solar system are several times larger than Jupiter.
(Originally published on 7.8)
New York Times
{Appeared in Haaretz newspaper, 8/8/2000}
