Encyclopedia of the Solar System 2nd ed

Physics and Chemistry of Comets 559

(a) (b)

(c)

FIGURE 2 Images of comet nuclei. A. Comet Halley nucleus composite. (Courtesy of H. U. Keller, Max-Planck-Institut f ̈ur

Aeronomie, Katlenburg-Lindau, Germany©CMPAE.) B. Comet Borrelly. (Courtesy of NASA/JPL.) C. Comet Wild 2. (Courtesy of

NASA and theStardustMission Team.) D. Comet Tempel 1. (Courtesy of NASA/JPL-Caltech/UMD.)

the shortest dimension is 4.9 km. The surface shows both
smooth and rough terrain, scarps (a line of cliffs usually
produced by faulting), and impact craters. The surface is
generally homogeneous in color and albedo, which varied

from 0.02 to 0.06, and the temperature of the surface in-

dicates an equilibrium with sunlight. Observations on ap-

proach detected numerous short outbursts that can be as-

sociated with specific regions on the surface.