Physics Department Seminar University of Alaska Fairbanks

J O U R N A L    C L U B


Ultraviolet Imagery of Comet P/Halley from Sounding Rockets

Robert McCoy
Director, GI, University of Alaska Fairbanks



In 1986 an ultraviolet imaging payload was launched twice from White Sands Missile range to image the coma of Comet P/Halley. The rocket payload contained two instruments, a direct-imaging camera to image H Lyman-α (1216 Å) from the comet and an objective grating spectrograph to image the coma (C, O, S) at wavelengths from 1300 Å – 1900 Å. Schmidt cameras with electrograph (film recording) detectors were used to converted ultraviolet photons to electrons which were accelerated into electron sensitive film.
The payload was first launched before sunrise on February 24, 1986 and reflown on 13 March. Both flights obtained good data but many of the H Lyman-α images on the first flight were marred by static electrical discharges in the film transport. The film transport was modified between launches which remedied that problem. Analysis of isophotes from images collected in the two flights yielded estimates of production rates of H, C, O and S atoms from the comet on those two dates. A model was used to analyze the shapes of the Lyman α isophotes providing information on the dynamics within the coma for H atoms produced by photodissociation of water within the comet.
The technology used in these rocket experiments was adapted from instruments flown to the moon on Apollo 16 by George Carruthers. The March launch was timed to coincide with the comet flyby of the European Giotto spacecraft. The imager on Giotto (built by Peter Delamere’s Dad) took images of the comet that are comparable to the recent images of Kuiper Belt object 2014 MU69 (Ultima Thule) obtained with the imager on the New Horizons spacecraft (Peter Delamere Co-I). Other spacecraft including Pioneer Venus, Dynamics Explorer and a Japanese mission made observations of H Lyman – α from Comet P/Halley.


Friday, 20 Sept 2019

Globe Room, Elvey Building