Pioneer Venus measurements of H, O, and C production in comet P/Halley near perihelion

The Pioneer Venus Orbiter Ultraviolet Spectrometer measured the production of H, O, and C in comet Halley from late December 1985 to early March 1986. Water production rates obtained from the H data rose from 3.3 x 10 to the 29th/s at 1 AU inbound to 1.2 x 10 to the 30th/s at perihelion; there was a further increase to 1.6 x 10 to the 30th/s followed by a slow decline to 1.4 x 10 to the 30th/s at the time of the Vega-1 encounter. The H measurements show a periodic behavior that imply variations in the water production rate having structure within a 7.4-day sidereal period, in phase with similar variations seen in radical and dust production in March and April. Average H:O:C ratios of 1.0:0.7:0.07 were measured from 10 to 26 days after perihelion.