Hundredth Planet Outside Solar System Discovered

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"It's thought that life, at least as we know it, would have liquid water," said McCarthy. The new planet would not be a likely candidate for life because it's probably composed mostly of gas, he said. "Liquid water, if it exists here, would sink."

McCarthy said it was possible that giant planets like the new one might have some moons, and the smaller bodies could harbor liquid water. Astronomers still have no way of detecting extrasolar moons.

Extrasolar Planetary Trends

Astronomers Paul Butler of the Carnegie Institute and Geoffrey Marcy of the University of California in Berkeley have predicted that about 12 percent of the sun-like stars in our galaxy, the Milky Way, have planets orbiting their stars within about 5 AU.

McCarthy said that with 100 extrasolar planets, a trend has emerged that supports the theory that giant planets in solar systems may form at great distances from their stars.

The giant outer planets are loosely packed concentrations of gas, but as they move nearer to their suns they solidify and become more compact—much like the inner planets of our own solar system, including the Earth.

"It is very difficult for a gas giant planet to form close to a star, because the most likely formation process for giant planets involves icy 'proto-planets' colliding, and such ices would likely evaporate close to the star," said McCarthy.

"In order to explain gas giant planets which orbit close to their star," McCarthy continued, "astronomers now believe that these gas giant planets formed in the outer solar system (around 5 AU) then moved inward, under the influence of a nebular disk of material which exerted a 'drag' on their orbit."

As more telescopes and time are being dedicated to the search, the rate of extrasolar planet discovery will increase, predicted McCarthy.

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