Pluto not largest of dwarf planets
Neighboring Eris is bigger, say UH and California scientists
Pluto can't seem to win. After being booted from the official roster of planets last year, it has lost its status as the largest of the "dwarf planets."
Its neighbor Eris is much larger, according to measurements made by California Institute of Technology researchers with data from the Big Island's Keck Observatory and the Hubble Space Telescope.
"Apparently we do have an object out there in the distant solar system more massive than Pluto," said University of Hawaii astronomer David Tholen, explaining the method used to determine the mass of Eris is "fairly reliable." The measurements indicate it is 27 percent heavier than Pluto.
Possibly another planet could be designated "if the International Astronomical Union changes course again in 2009 at a Rio general assembly," Tholen said.
Pluto was considered the largest solar system object found beyond Neptune but was demoted as the ninth planet last year in controversial action by the IAU. Eris was known as the "10th planet."
A new category was created for "dwarf planets" that included Pluto, Eris and Ceres.
Tholen said new observations from the Hubble telescope also should help clear up some puzzles about the nature and mass of the bodies in Pluto's system, including Charon, a large satellite discovered in 1978, and Nix and Hydra, two smaller moons discovered in 2005.
Tholen was among UH Institute for Astronomy scientists presenting their work at the semiannual meeting of the American Astronomical Society held in late May at the Hawaii Convention Center.
» Rolf-Peter Kudritzki, IFA director, reported on a new method used to measure extragalactic distances accurately. It is based on stellar gravities and temperatures of blue supergiant stars beyond the group of galaxies that contain the Milky Way. He and his collaborators observed the galaxy NGC 300, about 6 million light-years away in the constellation Sculptor, to test their method.
» Roy Gal of the IFA and Lori Lubin of the University of California at Davis led a group of astronomers who, for the first time, "mapped" where action is in a mega-structure in the distant universe. "We see unusually large numbers of galaxies with high star formation rate, producing over 100 suns per year, and with active central supermassive black holes," Lubin said.
» IFA astronomer R. Brent Tully and his collaborators discovered the Milky Way galaxy "lies at the edge of a huge void and is being repulsed by the void at high speed." They concluded that the void "is really empty," reporting, "Only a small fraction of the matter of the universe is in a visible form, so it is not a given that an apparently empty region is truly empty. However, the large push we are getting from the Local Void is convincing evidence that it really is empty."
Where concentrations of matter pull, a void in effect pushes, the scientists said. "If an object is surrounded uniformly by matter in all directions, except for one sector in which there is nothing, then the absence of a pull is a push away from that sector. ... Our velocity from the Local Void is 600,000 mph."