Photometric Variability of the Largest Kuiper Belt Objects: Evidence for Uniform Surfaces
Abstract
The large selfgravity of the dwarf planets should allow them to be near hydrostatic equilibrium, retain extremely volatile ices, have possible tenuous atmospheres, and be differentiated. Thus, the surfaces as well as the interior physical characteristics of the largest Kuiper Belt objects may be significantly different than the smaller, more primordial objects. Here we report new timeresolved light curves and determine the rotations and phase functions of ten large TransNeptunian objects, including Eris (2003 UB313), Orcus and 2002 AW197. Three of the smaller objects (2004 TY364, 2003 VS2, and 2001 YH140) show obvious rotational light curves. The median rotation period of KBOs is about 9+1 hours which is significantly longer than the median main belt asteroid rotations. No shortterm photometric variability was found for (136199) Eris to about the 0.01 magnitude level. This high signaltonoise photometry suggests Eris is nearly spherical with a very uniform surface. Such a nearly uniform surface may be explained by an atmosphere which is frozen onto the surface of Eris when near aphelion. The atmosphere, like Pluto's, may become active when near perihelion effectively resurfacing Eris every few hundred years. The methane rich KBO 2005 FY9 may also be in a similar situation. At about the 97% confidence level the largest KBOs show shallower Rband phase curves compared to smaller objects. This is consistent with the largest dwarf planets having higher albedos and icy surfaces. The absolute magnitudes obtained for individual objects are a few tenths of magnitudes different than that given by the Minor Planet Center. The values determined for each object using a linear reduced magnitude fit (mR(1,1,0)) and absolute magnitude fit (H and G formalism) are statistically the same to within a few hundreths of a magnitude. This work has been published in the Astronomical Journal: Sheppard, 2007, AJ, 134, 787.
 Publication:

AAS/Division for Planetary Sciences Meeting Abstracts #39
 Pub Date:
 October 2007
 Bibcode:
 2007DPS....39.3907S