EDITORIAL DESK

The Search for Livable Worlds

( Editorial ) 531 words

The pace of planetary discovery has been steadily quickening. A decade ago scientists did not know of even a single planet outside our solar system. Now they have found more than 100. Of course, they haven't actually seen them. They are far too distant and dim. Instead, scientists have inferred their presence from the slight wobbles their gravitational pull causes in their stars or from a slight dimming of a star's light as a planet passes across it.

Until last week, all the planets detected had been huge, gaseous blobs circling their suns at very close range. That is no surprise. The bigger and closer a planet is, the more likely it is to cause its star to wobble. But two American teams and one European team have now detected planets the size of Neptune or Uranus, some 14 to 20 times the mass of Earth. These planets, too, orbit their stars at too close a range for our form of life. But scientists say they are increasingly comfortable with the notion that there are an enormous array of planets out there, and that some of them are bound to be rocky orbs with temperatures that can permit liquid water and possibly life. Probably no Earth-size planet will be found until NASA launches a planet-hunting spacecraft in coming years.

Meanwhile, scientists searching for extraterrestrial intelligence will still scan electromagnetic waves reaching Earth for signs of a message that a far-off civilization may have sent.

The theory has been that radio waves or lightwaves are the fastest way to send messages across interstellar distances, so they are the most likely form of communication for an intelligent civilization. But an analysis in Nature this week suggests that a message longer than just a ''Hi, we're here'' kind of thing would be sent most efficiently in physical form, much like a message in a bottle. That suggests that we should be looking for the alien equivalent of a letter in our own planetary backyard, analogous to the monolith left on the moon by aliens in ''2001: A Space Odyssey'' by Arthur C. Clarke. The only hitch is that such a message, traveling at a crawl by space standards, might have been sent 30 million years ago, and who knows whether the senders would have moved on or died off in the eons since. Best not to give up on electromagnetic messages entirely.

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