Comet P/Halley

Image Source: NASA

Comet with 76-year orbital period. Images returned by the Giotto Mission revealed its nucleus was a dark (albedo 0.04-0.05), peanut-shaped body, ~15 km long and 7-10 km wide; the measured density (0.3 g/cm3) indicated a fluffy porous texture. The black surface is composed of organic compounds. Giotto imaged 7 jets on the warmer sunlit side (ejecting ~3 tonnes/s of material), but only ~10% of the surface was active. The jets gave the comet a strange, wobbling rotation. H2O accounted for ~80 % of the ejected material with substantial amounts of CO (10 %), CO2 (2.5 %), CH4 and NH3. Traces of other hydrocarbons, Fe, and Na were also found. Two major classes of dust particles were found: one dominated by the light elements (C, H, O, N); the other rich in mineral-forming elements (Na, Mg, Si, Fe, Ca), which must have been derived from closer to the Sun than its ices. Light elements (except N) occurred in the same relative abundances as in the Sun, confirming that Comet Halley is made of primitive solar nebular material.

Some or all content above used with permission from J. H. Wittke.