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Search for Another Earth Quietly Underway
By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
30 November 2000
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Small target, small telescope
Deeg and a colleague, Laurance Doyle of the SETI Institute, aren't waiting for a costly or complicated space mission. They're using a worldwide network of relatively small (1-meter, or 3 foot) ground telescopes to look for planets between 1.8 and 2.5 times the size of Earth -- the high end of what's considered potentially habitable.
Using a new search method, Deeg and Doyle watch for slight dips in starlight as a planet crosses in front of a star. (Astronomers have long used this technique to study Venus and Mercury as they cross in front of the Sun.)
This transit method, as it is called, can only spot planets whose orbits bring them in front of their host star as seen from Earth. Its first success came last November, but so far it has only been viable for spotting large planets closer to their host stars -- situations that generate large enough fluctuations in starlight to be detected from Earth.
So Deeg and Doyle have refined the method to find smaller planets using a smaller telescope. They take several readings over many days and add them together, boosting otherwise imperceptible signals to detectable levels. They've also confined their hunt to relatively small stars, where a planet's signal would be more obvious in relation to the total starlight.
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First Find |
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The very first planets found outside our solar system were detected by Penn State researcher Alexander Wolszczan and colleagues in 1992, using the Arecibo Observatory radio telescope in Puerto Rico.
One of the planets is 2.8 times as massive as Earth, and another discovered in the same system later is actually smaller than Earth. The central star, however, is a pulsating neutron star, and it bathes the planets in an intense, deadly radiation field.
Some scientists say these planets are not "normal," because they probably formed on the heels of a supernova, an explosion that turned a normal star into the remaining dense stellar corpse -- the neutron star -- that exists today. |
The two researchers have compiled reams of data on a star system called CM Draconis, 54 light-years away. A total of nine possible planets were identified in the data. Further observations showed that seven of these were not planets.
But Doyle is optimistic about the remaining two possibilities, putting the odds at 50-50 that one of them will be a planet less than 2.5 times the size of Earth.
Doyle says that regardless of whether or not they find an Earth-like planet around CM Draconis, their method shows that terrestrials can be detected using today's technology.
"We're saying that if you use these techniques, you can do the job," Doyle said. "It's not easy, but we don't have to wait for the next decade [to find] terrestrials."
Good morning, good morning
The first extrasolar Earth-like planet discovered might be a strange world, one where dawn is marked by a double sunrise. Why? Because Deeg and Doyle have so far confined their search to star systems called eclipsing binaries. These pairs of stars orbit each other in a plane that is parallel to our line of site -- meaning that they pass in front of each other.
A planet around a binary system would also most likely orbit in this same plane, which means the transit method could find it.
(Using the transit method, Deeg and Doyle would actually see two dips in the starlight as the planet passed in front of each star.)
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Uplink Your Views |
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Will we find another Earth? How long will it take?
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Doyle says they have also begun collecting data on crowded star fields. One picture contains more than 100 eclipsing binaries and more than 10,000 single stars.
So while Doyle says a satellite-based telescope could spot a terrestrial within a decade, he also makes it clear that such a discovery could happen much, much sooner, though he refused to offer a specific prediction.
"The answer could be forthcoming," he says.
Next page: But will there be life?
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