Posted at 2:24 p.m., Monday, June 18, 2007
Hawaii scope helps prove Pluto is not top dwarf planet
Washington Post
It's official: Not only is Pluto now a "dwarf planet," the category to which it was relegated last year, but scientists have determined that it is not even the largest of that new class.Using data from Hawai'i's W.M. Keck Observatory on Mauna Kea and the Hubble Space Telescope, scientists determined that Eris, an object in the solar system's Kuiper Belt, is larger than Pluto.
The discovery of Eris in 2005 and early estimates that it was probably larger than Pluto helped set off the controversy that resulted in Pluto's demotion from planet status. In a paper published in last week's issue of Science, California Institute of Technology astronomer Michael Brown has used precise calculations to show that Eris is 1.27 times the size of Pluto.
If Eris is not a planet, the International Astronomical Union decided last year, Pluto cannot be either. The decision prompted one of the most spirited debates about astronomy in a long time — countless schoolchildren protested Pluto's demotion to also-ran status.
Pluto and Eris, which was formerly known as Xena, are now considered dwarf planets — celestial bodies that have enough mass for their gravity to form them into nearly spherical shape but are small enough to be ruled, in gravitational terms, by other planets.
Brown studied the orbital movement of Eris's moon, Dysnomia, which allowed him to calculate Eris's mass. Scientists expect to find many other objects of similar size in coming years, which is why they decided it is impractical to call them all planets.
