The colour of Comet P/Halley's nucleus and dust

Abstract

Results are presented on the absolute calibration of the Halley Multicolor Camera (HMC), showing that HMC is 24 less sensitive than previously thought. The results are used to determine the reflectivity of the nuclear surface of the P/Halley comet, its color, and the color of the dust within 300 km of the nucleus. Results showed that the nucleus of P/Halley is red with respect to a solar spectrum; the spectral reflectance change in the range 440 to 810 nm is 6 + or - 3 percent per 100 nm scaled reflectance units per nm. The dust is reddened with respect to the sun by 7 + or - 3 percent per 100 mm between 650 and 810 nm, and 11 + or - 3 percent per 100 nm between 440 and 650 nm, in agreement with ground-based observations. The dust is thus more red than the nucleus.