NEW EXTRA-SOLAR PLANET DISCOVERED;CIRCULAR ORBIT SUGGESTS IT FORMED LIKE PLANETS IN OUR SOLAR SYSTEM
CAMBRIDGE, MA--The notion that giant, Jupiter-like bodies may be acommon occurrence around stars like the Sun has been bolstered by thediscovery of such an object orbiting Rho Coronae Borealis, a star inthe constellation Northern Crown. The newly discovered planet offersadditional evidence for how such systems form, and bolsters the ideathat other worlds like our own may be widespread throughout thegalaxy.
The discovery was made by a team of scientists from threeinstitutions---the Smithsonian Institution's Astrophysical Observatory(SAO) in Cambridge, MA, the National Center for Atmospheric Research(NCAR) in Boulder, CO, and the Pennsylvania State University in StateCollege, PA--based on observations made at the Smithsonian's FredLawrence Whipple Observatory on Mt. Hopkins, Arizona.
The scientific team includes Sylvain Korzennik, Martin Krockenberger,Peter Nisenson, and Robert Noyes of SAO; Harvard University graduatestudent Saurabh Jha; Timothy Brown and Edward Kennelly of NCAR; andScott Horner of Penn State.
Using a special instrument known as the Advanced Fiber Optic Echelle(AFOE) spectrograph located at the 1.5-meter Tillinghast Reflector ofthe Whipple Observatory, the scientists detected extremely smallvariations in the recession velocity of Rho Coronae Borealis that arethought to be caused by the presence of an orbiting companion.
With the AFOE capable of measuring velocity variations smaller than 10meters per second (about 22 miles per hour), the scientists found thatthe speed of Rho Coronae Borealis varied back and forth by about 67meters per second, or 150 miles per hour, over a 40-day period. Thisled the team to conclude that the star has a companion in a 40-dayorbit and, from the size of the velocity variation and the mass of thestar (almost identical to the Sun), they calculated that the companionmust be slightly more massive than the planet Jupiter.
The short orbital period means the planet must lie only about 1/4 ofan Astronomical Unit from the star---closer than Mercury orbits theSun (an AU is the distance of the Earth from the Sun). This alsoimplies its temperature would be about 300 degrees C, or more than 500degrees F--much too hot for liquid water to exist, and hence not alikely place for life to form.
According to the researchers, the circular nature of the orbitsuggests that the planet was formed like the planets in our own solarsystem, that is, through the slow coalescence of dust and gas from thecircularly rotating disk that is thought to surround all newbornstars. A more eccentric, or highly elliptical orbit, could imply thatthe companion object was a failed star, the unsuccessful secondpartner in a potential binary star system.
"This discovery helps show that giant planets like Jupiter may bereasonably common around ordinary stars," says Robert Noyes of SAO."Moreover, they can be found at a variety of distances from theirparent stars, ranging from very close in, like the companion to 51Pegasi, to very far away, like Jupiter relative to the Sun. Theplanet around Rho Coronae Borealis, like several others, is inbetween.
"It is exciting to think that there may be many smaller planets much more like the Earth in orbit around these stars, as in our own Solar System," says Noyes.
Timothy Brown, of NCAR, carried out the design andfabrication of the AFOE spectrograph's optics. He added, "All thegiant planets found so far orbit Sun-like stars. The star RhoCoronae Borealis is another one of these, but it appears tobe about 10 billion years old -- twice as old as the Sun."
Scott Horner, of Penn State, designed and built the AFOE's iodine cell(a precise velocity-reference device). "It was the star's solarsimilarity that led us to target it for study in the first place," heagreed. "Soon after we began to look at it, we thought that itsradial velocity was varying. Now, after 11 months of monitoring,we're sure."
As one of the stars forming the "crown" of the constellation, RhoCoronae Borealis is visible from February through September tonaked-eye observers in the Northern Hemisphere . It is about 50 lightyears from Earth.
A scientific paper describing the discovery has been accepted for publication in the Astrophysical Journal Letters. A pre-publication version of the paper has also been made available, along with other details about the AFOE program, on the World-Wide Web at http://www.cfa.harvard.edu/afoe. NCAR is sponsored by the National Science Foundation.
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