Astronomy: Evidence from a Distant Comet

The Ikeya-Seki comet may have seemed a dud to casual observers who were screened from its spectacular passage by assorted weather conditions. It was by no means a disappointment to astronomers. Never before has a comet undergone such detailed scientific scrutiny—from observatories around the world, from specially outfitted jet planes, from NASA’s sounding rockets.

Five times as luminous as a full moon, Ikeya-Seki lived up to its advance billing as one of the brightest comets of the century. Japanese astronomers boast that they snapped the clearest daylight pictures ever taken of a comet. Because of its close brush with the sun, Ikeya-Seki heated to an intensity that was easily recorded in detail by spectrographs, which gave scientists their strongest evidence so far of comet ingredients. Preliminary readings have already detected sodium, ionized calcium, iron, nickel, copper and potassium. Last week James Westfall, a young Caltech scientist, reported that his infrared observations of Ikeya-Seki were probably the first ever made of a comet. He is certain that the infrared emissions came from the comet itself and were not reflected sunlight. Analysis of this data should give scientists a better understanding of the structure and composition of comets.

Ikeya-Seki is now more than 55 mil lion miles away from the sun and gradu ally disappearing from sight. Early risers in the U.S. may still catch a glimpse at about an hour before sunrise if they look in the southeastern sky, above and to the right of where the sun rises. But it will be 500 to 1,000 years before Ikeya-Seki comes back into range and allows a check on current observations.