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Planet or failed star? Hubble finds strange object SPACE TELESCOPE SCIENCE INSTITUTE NEWS RELEASE Posted: September 7, 2006 Astronomers using NASA's Hubble Space Telescope have photographed one of the smallest objects ever seen around a normal star beyond our Sun. Weighing in at 12 times the mass of Jupiter, the object is small enough to be a planet. The conundrum is that it's also large enough to be a brown dwarf, a failed star.
Kevin Luhman of Penn State University in University Park, Pa., leader of the team that found the object, called CHXR 73 B, is casting his vote for a brown dwarf. "New, more sensitive telescopes are finding smaller and smaller objects of planetary-mass size," said Luhman. "These discoveries have prompted astronomers to ask the question, are planetary-mass companions always planets?" Some astronomers suggest that an extrasolar object's mass determines whether it is a planet. Luhman and others advocate that an object is only a planet if it formed from the disk of gas and dust that commonly encircles a newborn star. Our solar system planets formed 4.6 billion years ago out of a dust disk around our Sun. Brown dwarfs, by contrast, form just like stars: from the gravitational collapse of large, diffuse clouds of hydrogen gas. Unlike stars, brown dwarfs do not have quite enough mass to ignite hydrogen fusion reactions in their cores, which power stars such as our Sun. CHXR 73 B is 19.5 billion miles from its red dwarf sun. That's roughly 200 times farther than Earth is from our Sun. At 2 million years old, the star is very young when compared with our middle-aged 4.6-billion-year-old Sun. "The object is so far away from its star that it is unlikely to have formed in a circumstellar disk," Luhman explained. Disks around low-mass stars are about 5 to 10 billion miles in diameter. There isn't enough material at that distance from the red dwarf to create a planet. Theoretical models show that giant planets like Jupiter form no more than about 3 billion miles from their stars.
"It is important to study young star systems to understand how small bodies formed. Young brown dwarfs are brighter than older, cooler brown dwarfs. This allows them to be seen even at lower masses, where older dwarfs would still be undetectable," said team member John Wilson of the University of Virginia in Charlottesville. One way to further settle the uncertainty would be if a disk of dust could be observed around CHXR 73's companion. Like stars, brown dwarfs have circumstellar disks, too. They would be no more than about 2 billion miles in diameter. NASA's Spitzer Space Telescope has detected disks around several free-floating brown dwarfs. But CHXR 73 B is too close to its star for Spitzer to detect the disk. So astronomers will have to wait for the launch of the James Webb Space Telescope in 2013 to determine if this companion has a disk. The Webb telescope will combine Hubble's sharpness, which is needed for detecting close companions, and Spitzer's infrared sensitivity, which is necessary for seeing cool, dusty disks. The team's result will appear in the Sept. 20 issue of the Astrophysical Journal. |
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The Hubble Space Telescope has become astronomy's crown jewel for knowledge and discovery. The great observatory was placed high above Earth following its launch aboard space shuttle Discovery on April 24, 1990. The astronauts of STS-31 recount their mission in this post-flight film presentation.
Space shuttle Atlantis is delivered to Kennedy Space Center's launch pad 39B on August 2 to begin final preparations for blastoff on the STS-115 mission to resume construction of the International Space Station.
Just after 1 a.m. local time August 2, the crawler-transporter began the slow move out of the Vehicle Assembly Building carrying space shuttle Atlantis toward the launch pad.
Astronauts Jeff Williams and Thomas Reiter will conduct a U.S.-based spacewalk outside the International Space Station on August 3. To preview the EVA and the tasks to be accomplished during the excursion, station managers held this press conference from Johnson Space Center in Houston.
The long voyage of exploration to Jupiter and its many moons by the Galileo spacecraft began on October 18, 1989 with launch from Kennedy Space Center aboard the space shuttle Atlantis. The crew of mission STS-34 tell the story of their flight to dispatch the probe -- fitted with an Inertial Upper Stage rocket motor -- during this post-flight presentation film.
Space shuttle Atlantis is transported to the cavernous Vehicle Assembly Building where the ship will be mated to the external fuel tank and twin solid rocket boosters for a late-August liftoff.
