More Planets Emerge With Solar System-Like Orbits

At least two of the recently detected planets have approximately circular orbits. This characteristic is shared by two planets (one of them the size of Jupiter) previously detected by the same team around 47 Ursae Majoris, a star in the Big Dipper constellation, and one around the star Epsilon Reticulum. The majority of the extrasolar planets found to date are in an elongated, or "eccentric," orbit.

The further a planet lies from its star, the longer it takes to complete an orbit and the longer astronomers have to observe to detect it.

"As our search continues, we're finding planets in larger and larger orbits," said Steve Vogt of the Lick Observatory, University of California at Santa Cruz. "Most of the planetary systems we've found have looked like very distant relatives of the solar system - no family likeness at all. Now we're starting to see something like second cousins.

"In a few years' time we could be finding brothers and sisters."

"This result is very exciting," said Anne Kinney, director of NASA's Astronomy and Physics Division. "To understand the formation and evolution of planets and planetary systems we need a large sample of planets to study. This result, added to others in the recent past, marks the beginning of an avalanche of data which will help to provide the answers."

The recently detected planets range in mass from 0.8 to 10 times the mass of Jupiter, the largest planet in our solar system. They orbit their stars at distances ranging from about 0.07 AU (astronomical unit, or the distance from the Sun to Earth), to three AU.

The astronomers--from the United States, Australia, Belgium and the United Kingdom--are searching the nearest 1,200 stars for planets similar to those in our solar system, particularly Jupiter-like gas giants. Their findings will help astronomers assess the solar system's place in the galaxy and whether planetary systems like our own are common or rare.

For most of their discoveries, the astronomers have used the Keck 10-meter telescope on Mauna Kea, Hawaii; the Lick 3-meter in Santa Cruz, California; and the 3.9-meter Anglo-Australian Telescope in New South Wales, Australia. To find evidence of planets, the astronomers use a high-precision technique developed by Paul Butler, Carnegie Institution of Washington, and Geoff Marcy of the University of California at Berkeley to measure how much a star "wobbles" in space as it is affected by a planet's gravity.

The team also receives support from the UK and Australian governments.