The Shape and Surface Variation of 2 Pallas from the Hubble Space Telescope
Russell, C. T.; Stern, S. A.; Mutchler, M. J.; Parker, J. Wm.; McFadden, L. A.; Li, J. -Y.; Rivkin, A. S.; Thomas, P. C.; Bauer, J. M.; Schmidt, B. E.; Radcliffe, S. C.
United States
Abstract
We obtained Hubble Space Telescope images of 2 Pallas in September 2007 that reveal distinct color and albedo variations across the surface of this large asteroid. Pallas’s shape is an ellipsoid with radii of 291 (±9), 278 (±9), and 250 (±9) kilometers, implying a density of 2400 (±250) kilograms per cubic meter—a value consistent with a body that formed from water-rich material. Our observations are consistent with the presence of an impact feature, 240 (±25) kilometers in diameter, within Pallas’s ultraviolet-dark terrain. Our observations imply that Pallas is an intact protoplanet that has undergone impact excavation and probable internal alteration.