Infrared temporal development of P/Halley

Halley's comet was observed at 0.7 to 23 microns with several diaphragms and beam throws on over 30 occasions between 1985 Dec. 12 and 1986 May 6. Several times, once within hours of perihelion, simultaneous measurements were made with different beam sizes using telescopes in Minnesota and Wyoming. Halley has an average dust albedo of 12% at 120 deg scattering angle. There is no evidence for strong backscattering in the phase function to angles of 165 deg. The 10 microns silicate signature is always present but varies in strength for heliocentric distances less than 1 AU. It is absent at distances greater than 1 AU. The dust albedo appears to decrease when the silicate feature is weak. Halley's infrared intensity fluctuates by a factor of 7 on timescales of 1 to 2 days. The variations suggest jet-like activity associated with nuclear rotation.