"Snow White" (2007 OR10)
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2007 OR10 was discovered in 2007 by astronomers Margaret E. Schwamb, Michael E. Brown, and David L. Rabinowitz as part of Schwamb's PhD thesis (Mike Brown, blog entry of August 9, 2011). Currently 86 AUs out from the Sun, 2007 OR10 gets as close to the Sun as 33.5 AUs but moves as far out as 100.7 AUs, with an average orbital distance of 67.1 AUs, a period around 550 years, a high eccentricity around 0.5, and an inclination of 30.7 degrees (NASA Small Body Database Browser, August 29, 2011). Assuming that the object must be bright white as well as large to be visible despite its great distance, Brown nicknamed it "Snow White" for its presumed coloration. Further observations, however, determined that the object is one of the reddest objects in the Edgeworth-Kuiper Belt, comparable only to Quaoar.
In a pre-print uploaded on August 5, 2011, astronomers Michael Brown, Adam Burgasser, and Wesley Fraser submitted a paper analyzing data that show 2007 OR10 to be covered with significant deposits of water ice. Additional analysis also indicates that its red coloration is caused by small amounts of methane, as on Quaoar. Although 2007 OR10 is warmer than Quaoar, its greater mass enables it to retain small amounts of methane which reddened over time through exposure to the Sun's ultraviolet radiation (CalTech press release; Keck news release; and Brown et al, 2011).
2007 OR10 is now estimated to be larger than Quaoar (which was most recently estimated around 890 ± 70 kilometers (km) -- or 553 ± 43 miles -- in diameter and to have a density of around 4.1 ± 1.3 grams per cubic centimeter). Like Quaoar, 2007 OR10 probably shares a high density which suggests that the planetary object is composed primarily of rock, more like an inner-orbit asteroid, than the mostly volatile ices that outer orbit, Edgeworth-Kuiper Belt objects (EKO) like Pluto appear to be composed of. Based on assumptions of a similar albedo with a 50 percent variance, 2007 OR10 appears to be somewhere between the fourth and seventh largest object in the Edgeworth-Kuiper Belt (Brown et al, 2011).
On August 24, 2006, the International Astronomical Union (IAU) voted to establish a new category of Solar System objects called "dwarf planets." As 2007 OR10 is large enough to have a spherical shape, it is a candidate for IAU designation as a dwarf planet. It also appears to be a member of the Solar System's "scattered disk" of objects perturbed into orbits of high inclination as well as eccentricity.
More information and images of Pluto, Charon, and the Edgeworth-Kuiper Belt are available at NASA's Pluto-Kuiper Belt Mission and Planetary Photojournal. Fact sheets on Pluto and the Centaur object Chiron are also available from NASA's National Space Science Data Center.
David Seal (a mission planner and engineer at NASA's Jet Propulsion Laboratory at CalTech) has a web site that generates simulated images of the Sun, planets, and major moons from different perspectives and at different times of the year. Try his Solar System Simulator.
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