Earth-Sized Planet Found Just Outside Solar System

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WASHINGTON
(AP) — European astronomers say that just outside our solar system
they've found a planet that's the closest you can get to Earth in
location and size.

It is the type of planet
they've been searching for across the Milky Way galaxy and they found it
circling a star right next door – 25 trillion miles away. But the
Earth-like planet is so hot its surface may be like molten lava. Life
cannot survive the 2,200 degree heat of the planet, so close to its star
that it circles it every few days.

The
astronomers who found it say it's likely there are other planets
circling the same star, a little farther away where it may be cool
enough for water and life. And those planets might fit the not-too-hot,
not-too-cold description sometimes call the Goldilocks Zone.

That means that in the star system Alpha Centauri B, a just-right planet could be closer than astronomers had once imagined.

It's
so close that from some southern places on Earth, you can see Alpha
Centauri B in the night sky without a telescope. But it's still so far
that a trip there using current technology would take tens of thousands
of years.

But the wow factor of finding such a
planet so close has some astronomers already talking about how to speed
up a 25 trillion-mile rocket trip there. Scientists have already
started pressuring NASA and the European Space Agency to come up with
missions to send something out that way to get a look at least.

The
research was released online Tuesday in the journal Nature. There has
been a European-U.S. competition to find the nearest and most Earthlike
exoplanets – planets outside our solar system. So far scientists have
found 842 of them, but think they number in the billions.

While
the newly discovered planet circles Alpha Centauri B, it's part of a
system of three stars: Alpha Centauri A, B and the slightly more distant
Proxima Centauri. Systems with two or more stars are more common than
single stars like our sun, astronomers say.

This
planet has the smallest mass – a measurement of weight that doesn't
include gravity – that has been found outside our solar system so far.
With a mass of about 1.1 times the size of Earth, it is strikingly
similar in size.

Stephane Udry of the Geneva
Observatory, who heads the European planet-hunting team, said this means
“there's a very good prospect of detecting a planet in the habitable
zone that is very close to us.”

And one of the
European team's main competitors, Geoff Marcy of the University of
California Berkeley, gushed even more about the scientific significance.

“This
is an historic discovery,” he wrote in an email. “There could well be
an Earth-size planet in that Goldilocks sweet spot, not too cold and not
too hot, making Alpha Centauri a compelling target to search for
intelligent life.”

Harvard planet-hunter David Charbonneau and others used the same word to describe the discovery: “Wow.”

Charbonneau
said when it comes to looking for interesting exoplanets “the single
most important consideration is the distance from us to the star” and
this one is as close as you can get. He said astronomers usually impress
the public by talking about how far away things are, but this is not,
at least in cosmic terms.

Alpha Centauri was
the first place the private Search for Extra Terrestrial Intelligence
program looked in its decade-long hunt for radio signals that signify
alien intelligent life. Nothing was found, but that doesn't mean nothing
is there, said SETI Institute astronomer Seth Shostak.

The
European team spent four years using the European Southern Observatory
in Chile to look for planets at Alpha Centauri B and its sister stars
Alpha Centauri A and Proxima Centauri. They used a technique that finds
other worlds by looking for subtle changes in a star's speed as it races
through the galaxy.

Part of the problem is
that the star is so close and so bright – though not as bright as the
sun – that it made it harder to look for planets, said study lead author
Xavier Dumusque of the Geneva Observatory.

One
astronomer who wasn't part of the research team, wondered in a
companion article in Nature if the team had enough evidence to back such
an extraordinary claim. But other astronomers said they had no doubt
and Udry said the team calculated that there was only a 1-in-1,000
chance that they were wrong about the planet and that something else was
causing the signal they saw.

Finding such a
planet close by required a significant stroke of good luck, said
University of California Santa Cruz astronomer Greg Laughlin.

Dumusque
described what it might be like on this odd and still unnamed hot
planet. Its closest star is so near that it would always hang huge in
the sky. And whichever side of the planet faced the star would be
broiling hot, with the other side icy cold.

Because
of the mass of the planet, it's likely a rocky surface like Earth,
Dumusque said. But the rocks would be “more like lava, like a lava
planet.”

“If there are any inhabitants there, they're made of asbestos,” joked Shostak.

Copyright 2012 by The Associated Press. All rights reserved.

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