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Cold cloud may contain unseen solar dust.

Cold cloud may contain unseen solar dust

New astronomical findings show far less dust surrounding the sun than around similar stars, leading to speculation that the sun's "missing" dust actually lies in an unseen cloud encircling the solar system.

At the Jet Propulsion Laboratory in Pasadena, Calif., H.H. Aumann studied 36 of the nearest stars resembling the sun in color and temperature. As reported in the October ASTRONOMICAL JOURNAL, he found they typically emit 500 times more far-infrared radiation than our star apparently does. Aumann used data from the international Infrared Astronomy Satellite (IRAS), the only orbiting spacecraft that has recorded far-infrared emissions from space. Invisible energy that travels in waves less than a millimeter apart, far-infrared radiation usually arises from star-heated dust.

Sun-warmed dust beyond the outer planets theoretically could produce the "missing" energy, says T.N. Gautier of California Institute of Technology in Pasadena. That dust might exist within a cloud of comet nuclei that Dutch astronomer Jan H. Oort in 1950 predicted circles the sun at a distance at least 750 times farther than Pluto. Aumann says IRAS data might manifest Oort clouds around the sun's stellar peers without necessarily revealing one around the sun, because distant sources emit highly focused radiation, while a closer cloud would yield a diffuse signal.

Warmer dust in the solar system also obscures emissions from colder particles beyond the outer planets. Using the IRAS data, Aumann now is "trying to isolate the signal from the hotter stuff in the foreground so we can separate it out to see colder dust beyond."

Astronomers plan to intensify the search with powerful new satellite-based infrared telescopes, the first of which -- NASA's Cosmic Background Explorer (COBE)--is scheduled for launch in May 1989. "If a dust cloud is out there," says Michael G. Hauser of NASA's Goddard Space Flight Center in Greenbelt, Md., "COBE will see it." However, distinguishing it from other far-infrared sources may prove difficult because of COBE's extreme sensitivity.

The European Space Agency plans to launch an infrared-observation satellite by the mid-1990s, and NASA hopes to put another into orbit by 2000. But disproof of the dust cloud's existence could emerge earlier, Gautier says, if "theoretical consequences of such an abundance of material are shown to conflict with other observations."
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Author:Knox, Charles
Publication:Science News
Date:Oct 15, 1988
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