Infrared satellite leaves a bountiful legacy

IRAS - the Infrared (heat radiation) Astronomy Satellite - has greatly expanded astronomers' knowledge of the universe. Recently reported findings of its now completed 10-month mission, have shown:

* Something like 10 percent (more than 40) of several hundred nearby stars may be surrounded by orbiting debris such as that from which our own solar system planets once formed.

* ''An unexpectedly high percentage'' - some 25 percent - of galaxies may be colliding or interacting with each other.

* Comets are much dustier than had been realized. Long comet tails of ice and dust, unseen by visible light, show up in the infrared.

* Away from the plane of our own Milky Way galaxy, the sky seen at infrared wavelengths is dominated by spiral galaxies. Some of these emit 50 to 90 percent of their radiant energy in the infrared - ''an exciting and surprising result,'' according to IRAS scientists.

Such are the first fruits from a survey of nearly 98 percent of the sky that had been impossible before IRAS was orbited as a joint British, Dutch, and US project on Jan. 25, 1983.

Reported in the April 6 issue of the journal Science and presented this week to a meeting of the American Astronomical Society (AAS) in Baltimore, they give point to the cliche that astronomers didn't realize how much they had been missing. Now they have a heaping plateful of discoveries to follow up with further research.

This is typical of what happens when astronomers can view the cosmos at wavelengths that had previously been denied them. The advent of radio telescopes and X-ray observing satellites have given new perspectives on the universe. Now astronomers are able to study celestial objects and dust and gas by the heat radiation they emit - something nearly impossible without a satellite.

To quote from the report in Science by 12 IRAS scientists: ''Without IRAS, atmospheric absorption and the thermal emission from both the atmosphere and Earthbound telescopes (themselves) make the task of the infrared astronomer comparable to what an optical astronomer would face if required to work only on cloudy afternoons.''

This ability to ''see'' heat radiation has enabled IRAS sensors to detect dark material orbiting other stars. The stars Vega (fifth brightest in the sky) and Fomalhaut were found to be ringed by what appears to be small orbiting solid bodies. Now, Harmut H. Aumann of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. - one of the authors of the Science paper - told the AAS meeting such material may be orbiting more than 40 nearby stars. This is a sample of 335 stars within 75 light years of Earth. Perhaps 10 percent of nearby stars have such orbiting debris. This suggests, but does not yet prove, that the conditions for planet formation are widespread in our galaxy.

Another author of the Science paper, Carol J. Lonsdale of JPL, told the AAS meeting that recent studies of IRAS observations of about 20,000 galaxies shows that some 25 percent of galaxies with high infrared emission may be interacting with other galaxies. That's ''an unexpectedly high percentage,'' according to information released by JPL. Dr. Lonsdale explained that the shock of galaxy collision may trigger great bursts of star formation. This would heat interstellar dust and gas which would radiate strongly in the infrared. One such colliding galaxy pair - known by its catalog number Arp 220 - emits 100 times the power of a normal spiral galaxy, with 99 percent of this being radiated in the infrared.

B. Thomas Soifer of JPL and also an author of the Science report, pointed out that Arp 220 has the same characteristics as do some ''unidentified'' objects IRAS has discovered. He told the AAS meeting this suggests that such objects may also be galaxies. They would be more distant and even more luminous than Arp 220 .

Thus IRAS has given astronomers a very challenging new look at the universe.

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