Discovery! Earth-Size Alien Planet at Alpha Centauri Is Closest Ever Seen

Discovery! Earth-Size Alien Planet at Alpha Centauri Is Closest Ever Seen

This artist's concept shows the newfound alien planet Alpha Centauri Bb, found in a three-star system just 4.3 light-years from Earth. CREDIT: ESO/L. Calçada View full size image

The star system closest to our own sun hosts a planet with roughly
Earth's mass and may harbor other alien worlds as well, a new study
reports.

Astronomers detected the alien planet
around the sunlike star Alpha Centauri B, which is part of a three-star
system just 4.3 light-years away from us. The newfound world is about
as massive as Earth, but it's no Earth twin; its heat-blasted surface
may be covered with molten rock, researchers said.

The mere existence of the planet, known as Alpha Centauri Bb, suggests
that undiscovered worlds may lurk farther away from its star — perhaps
in the habitable zone, that just-right range of distances where liquid water can exist.

"Most of the low-mass planets are in systems of two, three to six or
seven planets, out to the habitable zone," study co-author Stephane
Udry, of the Geneva Observatory, told reporters today (Oct. 16).

So the discovery "opens really good prospects for detecting planets in
the habitable zone in a system that is very close to us," Udry added.
"In that sense, this system is a landmark."

Alpha Centauri Bb zips around its star every 3.2 days, orbiting at a
distance of just 3.6 million miles (6 million kilometers). For
comparison, Earth orbits about 93 million miles, or 150 million km, from
the sun. [Gallery: Nearby Alien Planet Alpha Centauri Bb]




This
wide-field view of the sky around the bright star Alpha Centauri was
created from photographic images forming part of the Digitized Sky
Survey 2. The star appears so big just because of the scattering of
light by the telescope's optics as well as in the photographic emulsion.
Alpha Centauri is the closest star system to the Solar System. Image
released Oct. 17, 2012.
CREDIT: ESO/Digitized Sky Survey 2

View full size image
A difficult detection

The research team, led by Xavier Dumusque of Geneva Observatory and the
University of Porto in Portugal, spotted Alpha Centauri Bb using an
instrument called the High Accuracy Radial velocity Planet Searcher, or HARPS.

HARPS is part of the European Southern Observatory's 11.8-foot (3.6
meters) telescope at the La Silla Observatory in Chile. The instrument
allows astronomers to pick up the tiny gravitational wobbles an orbiting
planet induces in its parent star.

In the case of Alpha Centauri
Bb, these wobbles are very tiny indeed; the planet causes its star to
move back and forth at no more than 1.1 mph (1.8 kph). It took more than
450 HARPS measurements spread out over four years of observing to
detect the planet's signal, Dumusque said.

"It’s an extraordinary discovery, and it has pushed our technique to the limit," he said in a statement.

The detection, to be published tomorrow (Oct. 17) in the journal
Nature, was so difficult that some astronomers aren't yet convinced that
Alpha Centauri Bb exists.

For example, Artie Hatzes of the Thuringian State Observatory in
Germany lauded the discoverers' technical achievement but said he
believes the jury is still out.

"As the American astronomer Carl Sagan
once said, 'Extraordinary claims require extraordinary evidence,'"
Hatzes wrote in a commentary piece in the same issue of Nature.
"Although a planetlike signal is present in the data, the discov­ery
does not quite provide the 'extraordinary evidence.' It is a weak signal
in the presence of a larger, more complicated signal. In my opin­ion,
the matter is still open to debate."

Udry, however, said that the team's statistical analyses show a "false
alarm probability" of just one in 1,000 — meaning there's a 99.9 percent
chance that the planet exists.

And some experts don't agree with Hatzes that Alpha Centauri Bb requires extraordinary supporting evidence.

"The reason why this seems to be an extraordinary claim is because
everyone has heard of Alpha Centauri B; it's a household name," said
Greg Laughlin of the University of California, Santa Cruz, who was not
part of the discovery team. "It's extraordinary not so much in terms of
the robustness of the result, but rather just in terms of the fact that
it's a well-known nearby star."

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A lava world?

Dumusque and his colleagues determined that Alpha Centauri Bb is about
13 percent more massive than Earth, suggesting it's a rocky world. In
addition to being the closest known exoplanet, it's also the first
planet with a mass similar to Earth ever found around a sunlike star,
researchers said. [Alpha Centauri Stars and Planet Explained (Infographic)]

Alpha Centauri Bb's extreme closeness to its parent star probably gives
the planet a surface temperature around 2,240 degrees Fahrenheit (1,227
degrees Celsius), making it unsuitable for life, researchers said.

"At this temperature, there is a lot of chance that the surface — if
it's made of rock, for example — it's not solid, but it's more like
lava," Dumusque told reporters today.

Even though it resides in a three-star system — consisting of
close-orbiting Alpha Centauri A and Alpha Centauri B, along with the
more distant Proxima Centauri — the newfound world's orbit is stable
over the long haul, Laughlin said. So are orbits in Alpha Centauri B's
habitable zone, he added.

Should we send a probe to study the newfound planet in Alpha Centauri up close?












It's possible that Alpha Centauri A and Proxima Centauri may host
planets as well, Udry said. The system will likely be the subject of
newly intense scientific scrutiny, as astronomers seek to confirm the
existence of Alpha Centauri Bb, learn more about it (such as whether or
not it has an atmosphere) and hunt for additional nearby alien worlds.

"If you want to envision exploring this system, then it's almost twice
as easy to get there as anywhere else," Laughlin said. "This is our
backyard, and to find out that planet formation did occur there is just
extraordinarily exciting."

Astronomers have now discovered more than 800 exoplanets,
but thousands more — including 2,300 detected by NASA's planet-hunting
Kepler Space Telescope to date — await confirmation by follow-up
investigations. Work so far suggests that small, rocky planets such as
Earth are quite common throughout our Milky Way galaxy.


Source:-
http://www.space.com/18089-earth-size-alien-planet-alpha-centauri.html