Jun 7 1984
From The Space Library
The research satellite orbiting Venus, Pioneer Venus Orbiter, briefly tilted to watch passing comet Encke and sent back information showing that the comet was losing water at a rate three times higher than earlier calculations predicted, scientists at Ames Research Laboratory reported. The surprising finding "could be due to the particular arrangement of ice and dust which comprise the comet or to crumbling of steep-sloped hills and mesas that may cover the surface of the 1.2-mile diameter of the comet nucleus," said NASA spokesman Peter Waller. He added that the finding might shed some light on the exact nature and makeup of comets.
Comets were "dirty cosmic snowballs" of dust, rocky materials, and ice, Waller said. "Whether the ice and dust are layered, mixed together in chunks, or form hills and valleys remains a mystery." Observations of the comet were made with an ultraviolet spectrometer, one of many scientific instruments aboard the orbiter, which detected light in the ultraviolet region of the spectrum. "Because most atoms emit ultraviolet light when they're bathed in sunlight, measuring the wavelength and intensity of the emitted light can give scientists an idea of what elements are in a sample as well as how much of an element or compound is present," said Dr. Ian Stewart of the University of Colorado. His team at the university built the spectrometer and calculated the comet's rate of water loss.
Johann Encke, a German astronomer who calculated the comet's orbit in 1818, noted that the comet was behaving abnormally, with the time it took to travel once around the Sun getting shorter in apparent contradiction to the laws of classical physics. Scientists now explained the phenomenon with the fact that comets spun slowly, like frozen tops. "The ice vaporizes, particularly when the comet is near the Sun and may cause a jet reaction that can change the comet's orbital path," Stewart said. (ARC Release 84-27; NY Times, June 10/84, 25)
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