Direct measurement of the size of 2003 UB313 from the Hubble Space Telescope
We have used the Hubble Space Telescope to directly measure the angular size of the large Kuiper Belt object 2003 UB313. By carefully calibrating the point-spread function of a nearby field star, we measure the size of 2003 UB313 to be 34.3 ± 1.4 mas, corresponding to a diameter of 2400 ± 100 km or a size ~5% larger than Pluto. The V-band geometric albedo of 2003 UB313 is 86% ± 7%. The extremely high albedo is consistent with the frosty methane spectrum, the lack of red coloring, and the lack of observed photometric variation on the surface of 2003 UB313. Methane photolysis should quickly darken the surface of 2003 UB313, but continuous evaporation and redeposition of surface ices appears capable of maintaining the extreme albedo of this body.
Additional Information© 2006 The American Astronomical Society. Received 2006 February 8; accepted 2006 April 3; published 2006 May 4. We would like to thank the director and staff at the Space Telescope Science Institute (STScI) for providing the opportunity to make these measurements and the assistance in making them happen. This research has been supported by a grant from STScI and from NASA Planetary Astronomy.
Published - BROapj06b.pdf
Submitted - 0604245.pdf