If proved toexist, the planets would be the most distant known.

The study, partof a project called the Optical Gravitational Lensing Experiment, or OGLE,involves very distant stars, all thousands of light-years away and beyond thosetypically surveyed for planets. A European news agency, Deutsche Presse-Agentur(DPR), first reported the results of four astronomers who said there is a"high probability" that many the 42 stars they winnowed out thelarger field may harbor planets.

The observations,made last summer using the Las Campanas observatory in Chile, were conducted byWarsaw University astronomers Andrzej Udalski, Marcin Kubiak and MichalSzymanski, along with Bohdan Paczynski of Princeton University.

The astronomers looked for dips in starlight that would indicate an object had passed in front of a star. The method, used by other research teams and planned for use on the space-based Kepler mission, so far has not been used as a primary means for discovering extrasolar planets.

"We observedmillions of stars looking for the 'transit' phenomenon which is essentially avery tiny lowering of the brightness of the star when an object, perhaps aplanet of very low mass, crosses between us and the star," Udalski toldDeutsche Presse-Agentur.

The researchers said they hope other astronomers will work to confirm the data in their study, which has been submitted to the journal Acta Astronomica and has also been posted on the Internet.

Cautious reception

One astronomerwho is an expert on the method of detecting planets by observing dips instarlight said it's statistically unlikely that most of the 42 detections inthe OGLE survey are actually planets, though some may be.

Laurance Doyle of the SETI Institute told SPACE.com that some or most of the transiting objects could be companion stars, possibly very dim, that orbit in a binary, eclipsing configuration around the target star.

Doyle said some binary stars graze their partners, as seen from our vantage point, and the light signal can be very confusing.

"You have tomake sure that it's not grazing, eclipsing binaries," Doyle said.

He added that the data collected so far by the OGLE team was not enough to determine whether any planets exist or not. The issue is about signal strength, which must be built up with multiple observations over time. In each of the 42 cases, the Polish astronomers have assumed a period and found points that fit that period but were not necessarily taken sequentially.

"What is needed is that a candidate is identified, and predictions are made as to when the next transit will occur, with follow up observations confirming it or ruling it out," Doyle said. "Ideally the false alarm rate -- the likelihood of being fooled by photometric error sources -- is computed from the noise so that one also knows how many additional transit events will constitute a true planet detection."

Statistically, there could about 10 or 12 planets in the OGLE survey, Doyle said, assuming large planets occur at the same rate in the region of the OGLE survey, near the galactic center, as they do nearer our Sun where other extrasolar planets have been found.

The fact that the researchers have put their data into the public domain, on the Web, may well yield some hard planet finds rather quickly.

"The OGLE consortium has generously provided planet hunters with a set of extremely interesting target stars, predicting the times when potential transit may occur," Doyle said. "It may not be long before perhaps as many as a dozen of these candidates may be confirmed."

Known exoplanets

There are currently about 80 known extrasolar planets. They have been found by noting a slight wobble in a star caused by the gravity of an orbiting planet.

No extrasolar planets have been photographed, and all are very large, typically as massive as Jupiter or larger. If there are planets in the OGLE survey they, too, are likely of the large variety. Most researchers expect that Earth-sized planets exist around other stars, but that it will take a space-based mission to detect them.

Doyle said that regardless of the final outcome of the OGLE study, he's encouraged by the method's promise. He said the raw OGLE data is of good quality and that the study shows that the transit method can, in fact, be used to discover many extrasolar planets at once.

The stars in the OGLE survey are so far away and so dim, however, that confirming the results will be extremely difficult using the "wobble" method and the large Keck telescopes in Hawaii, Doyle said.

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