Eight Extrasolar Planets Discovered Circling Sun-like Stars

By Keith Cowing
May 4, 2000
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Extrasolar PlanetsThe European Southern Observatory has announced the discovery of a collection of planet-sized objects circling stars similar to our sun. The discoveries were made by astronomers at the Geneva Observatory. The objects range in size from one planet somewhat less massive than Saturn to a very large object that is about 15 times the size of Jupiter.

According to ESO, six of the planets are most likely “bona-fide exoplanets” and the other two are apparently very low-mass brown-dwarfs. The smallest planet of this batch orbits the star HD 168746. ESO describes this star as being a “quiescent solar-like star of type G5 in the constellation Scutum (The Shield). It is slightly less massive than the Sun (0.92 solar mass) and is located at a distance of about 140 light-years.”

The planet orbiting HD 168746 does so in a circular orbit once every 6.4 days. The minimum mass of the planet deduced by the research team is only 80% of the mass of planet Saturn. It is important to note that this is only the third extrasolar planet discovered that is Saturn-sized or smaller. Until recently all extrasolar planets discovered were Jupiter-sized or larger.

In March 2000, NASA announced that the veteran planet hunting team of Marcy and Butler had discovered two planets that may be smaller in mass than Saturn thus breaking the boundary of what size planets could be detected orbiting other stars. As has been the case in the past, advances in planet hunting by one team quickly spawn advances by other teams. As planet hunting techniques become increasingly refined, smaller planets will be more easily detected. Only as these smaller worlds are detectable will we begin to be able to see if worlds similar to our own circle other suns.

Background Information

° Eight New Very Low-Mass Companions to Solar-Type Stars Discovered at La Silla, ESO press release

° NASA Announces a Significant Advance in Planet Hunting, SpaceRef

° Extrasolar Planets, SpaceRef Directory

° Very Early Planetary Formation Observed in Orion?, SpaceRef

° Hubble Confirms Abundance of Protoplanetary Disks Around Newborn Stars, Space Telescope Science Institute, 1994

° Hot Jupiters and Rare Earths: Planets are common. Are we?, SpaceRef

° NASA’s Ames Research Center Uses Transit Photometry to Confirm Existence of Extrasolar Planet Circling HD 209548, SpaceRef

° Six New Extrasolar Planets Discovered, SpaceRef

° Of Planetary Transits Near and Far, SpaceRef

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