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More Earth-Like

Posted on: Wednesday, 1 September 2004, 06:00 CDT

More Earth-like

3 newly discovered planets around other stars have size, structure that might support life

By SHANKAR VEDANTAM Washington Post

Wednesday, September 1, 2004

Washington -- Three new planets have been discovered in other solar systems and are the closest ever found to Earth in size, marking an important step in the search for planets that could support life elsewhere in the universe, scientists have announced.

The new planets are significantly smaller than the many dozens found so far and might even be rocky, as opposed to gaseous, an essential platform for life to evolve.

The scientists who discovered the three planets said they were probably too hot to support life themselves, although one has a lukewarm zone that could conceivably support biological organisms.

"These discoveries are going to bring us closer to answering the question: Are we alone in the universe?" Anne McKinney, the director of NASA's Universe Division, said at a Washington news conference Tuesday.

Astronomers speculated that the new planets might be "ice giants" like Uranus and Neptune or even giant hunks of iron and rock dubbed "super-Earths."

Many conditions would need to be met before anyone can ask whether other planets could support life. Candidates need to be at an optimal distance from a star, neither too hot nor too cold. They probably need liquid water, and they would not trap harmful radiation, as Venus does.

"The ingredients of life are abundant in the universe," said Geoffrey Marcy, a planet-hunter at the University of California at Berkeley, who helped make the new discoveries.

He referred to rocky planets as "petri dishes" where those ingredients could come together.

"We can't quite see Earth-like planets yet, but we are seeing their big brothers," said Marcy's partner, astronomer Paul Butler of the Carnegie Institution of Washington.

Two of the planets were announced Tuesday by teams of U.S. scientists, and the third was announced earlier in the week by a team of European scientists. While the Americans and Europeans squabbled over whose discovery came first and which planet was the smallest, all agreed that an important frontier in planet-hunting had been crossed.

The two planets discovered by the Americans were found orbiting around stars about 33 and 41 light-years from Earth in the direction of the constellations Leo and Cancer. A light-year refers to the distance light travels in a year, and both these stars -- called Gliese 436 and 55 Cancri -- are relatively nearby in astronomical terms.

The planet found by the Europeans is about 50 light-years away in the southern constellation Ara (the Altar), according to Didier Queloz, an astronomer at the University of Geneva who helped discover that planet, named mu Arae.

The Americans referred to the group of new planets as Neptune- sized; Neptune has about 17 times the mass of Earth. The Europeans described the planet they had discovered as "Uranus-sized," which is about 14 times the mass of Earth. The smaller the planet, the greater the odds that it is similar to Earth.

All scientists hunting for planets are hamstrung by an inherent problem: No planet outside our solar system is visible to the naked eye, even through the most powerful telescopes. Because planets do not emit light -- they only reflect it from the star they orbit -- they are essentially invisible.

In order to detect them, scientists use a sophisticated technique that measures changes in the light emitted by a star as a planet revolves around it. The technique tends to spot large Jupiter-like planets close to stars.

By finding smaller planets, scientists say, there is at least a chance that they are rocky planets, as opposed to gas giants.

Guessing the composition of the new planets is speculative, but Queloz said they could be rocky. He argued that gaseous planets often form at great distances from a star and then migrate toward it, collecting more mass in the process -- this is the leading theory to explain the many Jupiter-like planets with short orbits found so far. By contrast, a smaller planet found close to a star likely originated much closer to the star and was therefore probably rocky.

A fourth new planet, about the size of Jupiter, was reported Aug. 24 by another American group.

Knight Ridder News Service and The New York Times contributed to this report.

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