Researchers tracking Halley's comet have already discovered a few new and puzzling facts about the periodic visitor. Using the recently built radio telescope called the Very Large Array (for its several scopes arrayed over miles in New Mexico), astronomers have found that water is streaming off the comet at two to three times the rate expected from calculations made after the 1910 passing.
Comets are chiefly ice balls embedded with dust and rock, and they remain frozen until they near the sun, when their surfaces begin to sizzle. On Oct. 19, when the comet was about 190 million miles from the sun, Halley was sweating off two tons of water per second.
The water coming off the comet was seen to break up after some hours into oxygen and hydrogen. But looking at the watery stream through a radio telescope shows only a "hole" extending 30,000 miles around the comet. The appearance of the hole occurs because Earth-based telescopes cannot pick up the wavelengths of light given off by water; they are obscured by the Earth's soggy atmosphere.
Past the 30,000-mile hole, oxygen and hydrogen gases were detected extending out to 60,000 miles around the comet.
The astronomers were surprised to find the oxygen-hydrogen emission in "clumps" about the size of the Earth rather than in a continuous cloud, as had been expected. "No one had even hypothesized such clumps," said Imke de Pater of the University of California. Researchers so far have no explanation for the clumps.
An astronomer team, made up of de Pater, Patrick Palmer of the University of Chicago and Lewis Snyder of the University of Illinois, were the first to use the two dozen "dishes" arranged in a grid at the Very Large Array to observe a comet. The array provided resolution 20 times better than that of a single telescope.