SEARCHING for alien planets circling other stars may seem to be merely a romantic quest for a handful of astronomers. But for the National Aeronautics and Space Administration it could help provide a guiding theme for space exploration as the agency struggles to redefine its mission.
That theme would be to complete the Copernican revolution, says Robert Brown of the Space Telescope Science Institute in Baltimore. Copernicus changed humanity's stellar view by showing that the sun - not Earth - is the center of that system. ``By discovering other planetary systems, we'll complete another facet of that revolution, which is to put our solar system in the context of planetary systems universally,'' Dr. Brown explains.
Technology has progressed to the point where astronomers now can specify the instruments and techniques needed to image alien worlds. And they can reasonably expect some of those instruments to be in place over the next 10 years. Thanks to ``the great investment'' that has been made in both ground-based and space-based astronomy, ``we're finally on the verge of being able to actually detect [alien] planets,'' Brown said.
In this outline presented during the annual meeting here of the American Association for the Advancement of Science (AAAS), Brown noted that the ``climate change'' in Washington is forcing the agency to rethink its whole rationale for science. Pursuing science for its own sake no longer justifies funding.
There has to be a more direct benefit for taxpayers. NASA ``is seriously contemplating using this theme of the search for other planets,'' Brown said, because it reaches beyond the interests of specialists and deals with questions of universal interest - such as, are we alone here, or are there other habitable worlds? And the quest for answers would also sharpen the strategy for exploring our own solar system.
NASA administrator Daniel Goldin cast his speech for the AAAS meeting in a similar perspective. It is a time, he said, when ``we're being asked literally to justify our existence.'' He explained that this means ``a leaner, but more agile and focused NASA.'' He added: ``Given that there is little or no new money available for science, we need a new paradigm to decide priorities.'' A long-term program to more clearly understand Earth's nature and place in the planetary system could guide the setting of those priorities, Brown said.
The technology that makes it possible to seriously plan to search for other ``Earths'' has developed rapidly. As Mr. Goldin observed: ``Twenty, even 10 years ago, this stuff would have been pie-in-the-sky. Now, we're not just talking what-if. We're talking about the nuts and bolts of how to do this.''
SOME of the search would be ground-based. Some would be done from space. Brown explained that, given the Hubble Space Telescope's new clarity of vision, instruments can be built that would allow Hubble to suppress the glare from a star sufficiently to see Earth-like planets around it. The next Hubble service mission is to carry a replacement camera in 1999. That camera could include this planet-seeking capability. So could another new instrument due to be placed on Hubble in 2002 or 2005.
Another powerful technique is to use two or more telescopes in unison either on Earth or in space. Computer processing of the telescopes' signals yields a far sharper image than any one telescope has alone. The farther apart the telescopes are, the sharper the image. It now appears possible to construct such a system that would be sharp-eyed enough to see planets orbiting at least relatively nearby stars. It would image the planets well enough to allow analyses of their atmospheres for possible life-related chemicals.