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Finding planets around ordinary stars.


The news flashed through the astronomical community like a lightning bolt: Astronomers have found two examples of planets orbiting ordinary stars that lie close to our sun.

At a meeting on low-temperature stars 2 weeks ago in Florence, Michel Mayor and Didier Queloz of Geneva Geneva, canton and city, Switzerland
Geneva (jənē`və), Fr. Genève, canton (1990 pop. 373,019), 109 sq mi (282 sq km), SW Switzerland, surrounding the southwest tip of the Lake of Geneva.
 Observatory reported strong evidence that a planet almost as massive as Jupiter orbits a familiar, sunlike star a mere 42 light-years from our solar system. The finding represents the first time that astronomers have inferred the presence of a planet orbiting a star similar to our sun. Earlier, researchers had detected planets around a pulsar, an extremely dense, rapidly spinning star that emits radio waves Radio waves
Electromagnetic energy of the frequency range corresponding to that used in radio communications, usually 10,000 cycles per second to 300 billion cycles per second.
 (SN: 3/5/94, p.151).

"It's a big, big step," says J. Roger Angel, director of the Steward Observatory Mirror Laboratory in Tucson.

Circling the star 51 Pegasi at just one-twentieth the distance of Earth from the sun, the newly discovered planet is lost in the glare of its bright parent star. No telescope can image it. Only a tiny wobble wobble /wob·ble/ (wob´'l) to move unsteadily or unsurely back and forth or from side to side. See under hypothesis.

wob·ble
n.
1.
 in the motion of 51 Pegasi, monitored over a 2-year period with a visible-light spectrograph at the Observatoire de Haute Provence in Saint Michel, France, betrays the gravitational grav·i·ta·tion  
n.
1. Physics
a. The natural phenomenon of attraction between physical objects with mass or energy.

b. The act or process of moving under the influence of this attraction.

2.
 tug of the massive planet. The planet revolves around the star, a resident of the constellation Pegasus, once every 4.2 days, causing the periodic wobble.

Last week, Geoffrey W. Marcy and R. Paul Butler Paul Butler is an astronomer who searches for extrasolar planets. He has co-discovered two thirds of the approximately 233 extrasolar planets discovered to date.

He received a BA and an MS from San Francisco State University, completing a Master's thesis with Geoffrey Marcy,
, both of San Francisco State University     [  and the University of California, Berkeley The University of California, Berkeley is a public research university located in Berkeley, California, United States. Commonly referred to as UC Berkeley, Berkeley and Cal , observed the orbit of 51 Pegasi for four nights with the Lick Observatory's 3-meter telescope on Mount Hamilton in California. Marcy told Science News that he and Butler detected virtually the same wobble as the Swiss team.

"I have no doubt at all about our result, but it's nice to have the external confirmation to convince other people," says Mayor. Adds Marcy, "We're excited that one of the most compelling questions in astrophysics astrophysics, application of the theories and methods of physics to the study of stellar structure, stellar evolution, the origin of the solar system, and related problems of cosmology.  [whether any planets orbit sunlike stars] has been answered."

That confirmation leaves other questions open. Some astronomers have wondered how a planet with roughly the mass of Jupiter can survive so close to a star nearly as hot as the sun. Adam S. Burrows of the University of Arizona (body, education) University of Arizona - The University was founded in 1885 as a Land Grant institution with a three-fold mission of teaching, research and public service.  in Tucson calculates, however, that even if the planet were mostly gas, like Jupiter, its gravity would prevent 51 Pegasi from boiling away the material. Nonetheless, the star's heat may have caused the planet to swell. It remains unclear whether the planet formed at its current location or the star dragged it in from a more distant orbit.

As if one finding wouldn't suffice, a second discovery has kept planetary scientists abuzz. At the Florence meeting, astronomers described near-infrared images and spectra of an object about 20 times the mass of Jupiter circling the tiny star GL229, located 30 light-years from Earth.

The finding, based on observations with several telescopes at Palomar Observatory near Escondido, Calif., differs in several respects from that announced by the Swiss team. GL229 has about four-tenths the mass of the sun, and the planetlike object it harbors orbits much farther away--about 44 times Earth's distance from the sun, says co-investigator Shrinivas Kulkarni of the California Institute of Technology California Institute of Technology, at Pasadena, Calif.; originally for men, became coeducational in 1970; founded 1891 as Throop Polytechnic Institute; called Throop College of Technology, 1913–20.  in Pasadena.

Kulkarni and his colleagues, including Ben Oppenheimer and Tadashi Nakajima, also of Caltech, note that the massive body could be either a planet or a brown dwarf--an object that forms as stars do but lacks the mass to sustain nuclear burning (SN: 9/23/95, p.200). "It's not clear exactly what the boundary [in mass] is between a planet and a brown dwarf," notes Kulkarni.

The presence of methane in the object's spectra has grabbed the attention of astronomers. If the body were a star, its intense heat would have destroyed the methane. "To my mind, the big difference [between this and previous brown dwarf candidates] is the apparent presence of methane," notes Jonathan I. Lunine of the University of Arizona. Other candidates, he says, are much more massive and straddle In the stock and commodity markets, a strategy in options contracts consisting of an equal number of put options and call options on the same underlying share, index, or commodity future.  the line between star and brown dwarf. "It's been a long struggle to find a brown dwarf, and this is the clearest example," says Burrows.
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Author:Cowen, Ron
Publication:Science News
Date:Oct 21, 1995
Words:691
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