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Possible Planet Hatchery Found in Deep Space - 2002-06-19


Astronomers have found a distant star like our Sun going through a persistent, but unusual type of eclipse, suggesting it may be at the center of a planet hatchery. The frequent darkening of the star may give scientists their first chance to observe the birth of a solar system like ours.

For seven years, astronomy students at Wesleyan University in Connecticut have been tracking a star 2,400 light years away from us in the Unicorn or Monoceros constellation. What has kept them preoccupied is a periodic darkening of the star's light.

"Essentially the star winks at us," said Wesleyan astronomy professor William Herbst. "Frankly, we didn't believe this. We had never seen a star behave quite this way and we thought it was probably our instrument or something funny or whatever."

The findings were so tantalizing that the Wesleyan astronomers wanted full-time global observations, so they persuaded colleagues in Hawaii and other U.S. states, Chile, Spain, Germany, Israel, and Uzbekistan to have a look.

They confirmed that the eclipses of the star occur every 48 days and last for 18 days. They are not the result of another body blocking its light, however, as in an eclipse of the sun or moon. Instead, Mr. Herbst said waves of dust and rocks, perhaps embryonic planets, are swirling around it, building to a crest that subsides after 18 days. It is this crest that dims the star from our view.

Professor Herbst said, "It's being blocked by a bunch of dust or asteroids or planetesimals [tiny planets] or rocks. We actually know that this dust is not just ordinary interstellar dust, but it's larger. It's grown."

The clue to this is the color of the star's light. If the material circling the star were tiny grains of dust, the light would be redder than it is because the grains scatter the blue frequencies of the light spectrum. But this light actually gets bluer when it dims.

Adding to the evidence that the astronomers may be observing a planet nursery is the very fact that the material blocking the star crests periodically as a wave.

According to U.S. space agency astronomer Geoffrey Bryden, this suggests that a body or bodies such as a planet or two might be disturbing the material as it swirls around the star.

Mr. Bryden said, "It's a little analogous to throwing a pebble into a pond in that the waves are excited at a particular point and then they propagate outwards."

The region of observation is close to the star in cosmic terms, less than the distance between our Sun and the nearest planet, Mercury. Because the star is only three million years old, William Herbst says scientists may be witnessing the birth of stars in a very young solar system.

Professor Herbst continued, "This star is, as far as we can tell, like the Sun was when it was three million years old. So the processes that are going on in this inner disk region, which is where the terrestrial [rocky] planets would be forming, could be analogous to what was going on with the formation of the Earth."

So far, astronomers have discovered 90 fully formed planets outside our solar system orbiting stars billions of years old like the Sun. But an astronomer not connected with the research team, Alan Boss of the Carnegie Institution in Washington, said the Wesleyan University findings are unique. Mr. Boss said, "This gives a chance to see what's happening right down in the maelstrom of where terrestrial planets are presumably forming. Just the fact that there may be a planet in orbit there around a star which is roughly three million years old may tell us something important about how rapidly planets form."

Wesleyan's William Herbst said his notions are hypotheses, so he brought his data to the conference on planets to get the views of his peers.

U.S. space agency astronomer Steve Maran said the findings will stimulate searches for similar phenomena around other stars. Mr. Maran said, "I think there will be a lot of interest in this kind of system."

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