An extrasolar planet that might be smaller than Jupiter has been found orbiting a star similar to our Sun, carving a circular orbit that is farther away from the star than Mars is from our Sun.
It's the second planet found around the star called 47 Ursae Majoris, creating a picture of a solar system that might be similar to ours and adding evidence to the idea that researchers eventually will find Earth-like planets. The star 47 Ursae Majoris is a yellow star similar to the Sun, estimated to be seven billion years old and located about 51 light-years from Earth. It lies in the Big Dipper.
The newly found planet is at least three-fourths the mass of Jupiter, researchers say, though it may be larger. It orbits the star at a distance that, in our solar system, would place it beyond Mars but within the orbit of Jupiter. Its previously found sister planet is estimated to be more than twice as massive as Jupiter.
Most extrasolar planets have been found to be larger than Jupiter, and many of them orbit as close to their host stars as Mercury is to our Sun. These previous findings have forced astronomers to question whether other solar systems form and operate the way ours does.
But one reason only large exoplanets have been found is that scientists detect them by noting a gravitational wobble in the host star. The method is not refined enough to spot small planets orbiting at great distances.
The new finding shows that the technique is improving and our picture of other solar systems may soon change. Evidence has been found for some 70 exoplanets.
"For the first time we have detected two planets in nearly circular orbits around the same star," said team member Debra Fischer of the University of California at Berkeley.
Fischer explained that most of the extrasolar planets found to date are in bizarre solar systems, with extremely short and rapid orbits that make for quick "years" (a year on Earth is determined by the time it takes the planet to orbit the Sun). Orbits of exoplanets are also typically erratic and oddly shaped.
"As our sensitivity improves we are finally seeing planets with longer orbital periods, planetary systems that look more like our solar system," Fischer said.
Fischer works with a team of planet hunters supported by the National Science Foundation and NASA. Her colleagues include includes Geoffrey Marcy, also of Berkeley, Paul Butler of the Carnegie Institution of Washington, Steve Vogt of the University of California at Santa Cruz, and Gregory Laughlin of NASAs Ames Research Center.
The team is responsible for the majority of extrasolar planets found since the first was recorded in the mid-1990s.
"Every new planetary system reveals some new quirk that we didn't expect," said Marcy. "We've found planets in small orbits and wacky eccentric orbits. With 47 Ursae Majoris, it's heartwarming to find a planetary system that finally reminds us of our solar system."
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