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The search for habitable planets: Are we alone in the universe?

DANIEL GOLDIN is urging space scientists to search for a habitable planet among the stars. That would have seemed quixotic a decade ago. But the administrator of the National Aeronautics and Space Administration (NASA) isn't tilting at windmills.

Thanks to astronomy's evolving technology, the quest now looks feasible. In fact, its preliminary stage has already produced impressive results. Witness last week's report from a Hubble Space Telescope observer.

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C. Robert O'Dell of Rice University in Houston announced that many young stars in the Orion Nebula have the kind of surrounding disks of dust and gas from which astronomers think planets form. These new Hubble photos sharpen the view of the disks, whose original discovery was announced two years ago. At that time, the telescope's blurry vision limited the conclusions Dr. O'Dell could draw.

Now the repaired telescope clearly shows a star at the center of each disk. It also shows enough detail for O'Dell and his colleague Zheng Wen of the University of Kentucky at Lexington to determine accurately the mass of the outer rim of one of the disks. They find at least several times the mass of Earth. Clearly, these disks have plenty of material to make planets.

This fits neatly with astronomers' current theory of planet formation. It goes like this: An interstellar cloud of dust and gas condenses to form a star. Left-over material spreads out into a swirling disk. As the young star evolves, it blows away much of the disk. Enough material remains to agglomerate first into grains and larger clumps and eventually into planets, asteroids, and comets. Planets with the right mass and materials and at favorable distances from the star may then form atmospheres, oceans, and other elements of environments favorable for the rise of organic life.

Astronomers have begun the search for such habitable planets by looking for the primordial disks around new stars. That's what the Orion Nebula provides. Located some 1,500 light-years from Earth - the distance light travels in 1,500 years - it is an active stellar nursery. O'Dell and Wen have found 56 disks out of a sample of 110 new stars.

This caps a decade of discovery that has provided tantalizing glimpses of such disks. The American-British-Dutch Infrared Astronomy Satellite - orbited in 1983 - has found indications of them by the infrared radiation they emit. Telescopes have seen disks around several relatively mature stars, such as Beta Pictoris, which is only 56 light-years away.

The next phases of the search will involve looking for such things as signs of the gravitational interaction of a star and planets. Actually finding a habitable planet must await technology that will allow imaging a star's planetary system and assessing the chemical makeup of likely planets.

NASA is beginning a search program that will include studying 100 nearby stars for signs of Jupiter-size planets. But Mr. Goldin's challenge to space scientists has a larger vision. He suggests the search for a habitable alien planet be the overarching goal that sets the agenda for all space research.

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It's questionable whether or not Congress and the American public would find that a compelling reason for funding the space program. On the other hand, it does tackle one humanity's enduring questions: Are we alone in the universe?

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