Tuesday, January 07, 2003, 12:11 a.m. Pacific Permission to reprint or copy this article/photo must be obtained from The Seattle Times. Call 206-464-3113 or e-mail resale@seattletimes.com with your request. Using new method, scientists find planet By Eric Sorensen Seattle Times science reporter Astronomers meeting in Seattle say they have found the most distant planet yet seen, using a method that promises to find ever-greater numbers of new planets, including those similar to ours. "Basically the door has been thrown wide open to go and discover a new Earth," said Dimitar Sasselov, a Harvard University professor of astrophysics and leader of the team that found planet OGLE-TR-56b. The discovery, announced yesterday at the annual winter meeting of the American Astronomical Society, will be published later this month in the journal Nature. It's a weird, Jupiter-sized planet. It orbits closer to its star than any known planet, about 50 times closer than the Earth to the Sun. The time it takes to make one orbit is just 29 hours. At an estimated 3,100 degrees Fahrenheit, it rains iron. Equally impressive is that the planet was found about 5,000 light years away in the Sagittarius arm of our galaxy, more than 30 times farther than the farthest of the 100 or so other planets found outside our solar system. Sasselov said this was made possible by a method called transit searching. In transit searching, astronomers look to see a planet passing directly in front of the star it is orbiting, as happens during a solar eclipse. A slight drop in the star's intensity signals that a planet is passing by. Until now, astronomers have looked for so-called extrasolar planets with radial velocity searches, which detect the slight wobble of stars caused by the gravitational pull of planets orbiting them. David Wilner, an astrophysicist and Harvard colleague of Sasselov's, said radial-velocity searching is limited to large planets with enough mass to affect their parent stars. The transit method lets astronomers detect planets one-fourth to one-half the size of Earth. The problem is the planet must be observed constantly, "without blinking," lest one not see it pass in front of its star, said Wilner. And since Earth-based observatories spend much of their time in daylight or facing in the wrong direction, a good inventory of distant planets needs to be done from space. NASA's $299 million Kepler Mission plans to do that starting in 2006. The planet OGLE-TR-56b was one of 59 candidates examined first at the Fred J. Whipple Observatory in Arizona and the Las Campanas Observatory in Chile. Most were not planet-sun combinations but binary stars, with five remaining candidates examined by the Keck Observatory in Mauna Kea, Hawaii, the largest optical telescope in the world. That narrowed the field of candidates to three: OGLE-TR-56b and two others that need to be looked at more. OGLE-TR-56b is the type of discovery that promises to come out pretty regularly at the AAS meeting, where thousands of scientists are showcasing how they can now probe the far reaches of the universe. The meeting, which is closed to the public, runs through Thursday at the Washington State Convention and Trade Center. The volume of announcements has the society holding as many as three press conferences a day. Only moments before Sasselov spoke yesterday, Fred Vrba of the U.S. Naval Observatory in Flagstaff, Ariz., announced the discovery of a brown dwarf 19 light years away in the constellation Eradanus. The brown dwarf, called 2 MASS 0415 for short, is so small and so cold that it threatens to blur our current definitions of a star. Brown dwarfs are objects that, unlike stars, are too low in mass to burn hydrogen but are more massive than planets. Astronomers don't know the size of 2 MASS 0415 but figure it is about one-500,000th the mass of the Sun and only 770 degrees Fahrenheit. "It's not much hotter than a household oven," said Vrba. "It's probably similar to a pizza oven, I would guess." Eric Sorensen: 206-464-8253 or esorensen@seattletimes.com.