"One side is blowtorched, and the other side is dark and cold," he said. But in between, he added, "there is a ring where the temperatures are lukewarm."
The other planet is about 18 times Earth's mass, and revolves around its star every 2.8 days. This planet is part of a solar system where three other planets were discovered previously, making that the solar system that most closely resembles our own.
Paul Butler, with from left, fellow scientists Geoffrey Marcy, Anne Kinney, Barbara McArthur and Alan Boss announces the discovery of planets outside the solar system.
(James M. Thresher -- The Washington Post)
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Graphic: Description of the size, composition, along with artist's concept of planet's appearance
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Video: Astronomers announce the discovery of 3 Neptune-size planets.
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Barbara McArthur of the University of Texas at Austin, who helped discover that planet, said scientists "don't know what it is composed of, but it could be rocky." The planet is too close to the star and too hot to support life, she said.
Marcy said there are about 20 billion planetary systems in the Milky Way galaxy alone -- meaning that scientists are at the very start of their search for planets similar to Earth.
The planet discovered by the European team had an orbit of about 9.5 days, Queloz said, and is also too hot to support life.
While the Europeans announced their discovery to the public ahead of the Americans, the Americans had beaten their competitors in submitting findings for scientific publication several weeks ago, said Alan Boss, an astronomer at the Carnegie Institution of Washington who offered comments on the new findings at a briefing at NASA headquarters yesterday. The Europeans, he said, submitted a paper for publication only last week.
"I would award them the bronze [medal] this time," Boss said.
In an e-mail, Stephane Udry and Michel Mayor of the European team said they took strong objection to the Americans' describing the European finding as "preliminary." And they contested the claim that the two planets found by the Americans were the "smallest extra-solar planets yet."
"This is obviously wrong," the European scientists wrote, arguing that they had found the smallest planet to date.
At the NASA briefing yesterday, Butler said all the planets were about the same size. He dismissed the idea that there was a difference between Uranus-sized planets and Neptune-sized planets, saying, "It's ridiculous."
