An international team of astronomers has discovered eight new extrasolar planets, at least two of which have circular orbits reminiscent of the planets in our solar system.
The latest discoveries, reported Monday, bring the total of known planets outside our solar system to around 80. More important, they circular orbits reinforce a growing realization that at least some other planetary systems are similar to our own.
Only a handful of previously discovered extrasolar planets have showed similar orbital characteristics, whereas others have had orbits that are more elliptical in shape.
"As our search continues, we're finding planets in larger and larger orbits," said Steve Vogt of the Lick Observatory at the 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," Vogt said. "Now we're starting to see something like second cousins. In a few years' time we could be finding brothers and sisters."
Astronomers do not yet know for sure whether planets around other stars form similarly to the planets in our solar system, or if entirely different mechanisms might be at work. Researchers have not yet found enough planets around enough stars, nor can they study them with great enough resolution.
And most of the planets they have studied are very unlike the planets near Earth. They are huge, typically larger than Jupiter, but often orbit their stars as close as Mercury orbits our Sun.
The eight newly detected planets orbit their stars at distances ranging from about 0.07 AU to 3 AU. (One AU, or astronomical unit, is the distance from Earth to the Sun.) They range in mass from 0.8 to 10 times the mass of Jupiter, the largest planet in our solar system.
The study, one of many similar ones in recent months, again illustrates that the pace of exoplanet discovery is increasing. The first planet outside our solar system was detected in 1995.
Anne Kinney, director of NASA's Astronomy and Physics Division, said the new finds presage an avalanche of new discoveries that will allow researchers to begin to unravel some of the mysteries about how planets and planetary systems form, in general.
The discovery was part of an ongoing search for planets around the nearest 1,200 stars.
The astronomers use the Keck 10-meter telescope on Mauna Kea, Hawaii, the Lick 3-meter telescope in Santa Cruz, and the 3.9-meter Anglo-Australian Telescope in New South Wales, Australia. They employ a pioneering technique called the wobble method, in which a star wobbles space as it is affected by a planet's gravity.
The research was supported by the National Science Foundation (NSF) and NASA.
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