Astronomers have discovered a rocky, Earth-mass planet right in
our own suns galactic neighborhood. The planet is orbiting a star a
mere 4.4 light-years away in the multiple-star Alpha Centauri
system, which may well turn out to be a cosmic condo, hosting
A habitable planet could well be among them, some astronomers
The planet, with an estimated mass 1.13 times higher than
Earth's, is orbiting Alpha Centauri B, which forms a binary pair
with Alpha Centauri A. Both essentially share the sun's mass and are
only slightly older than the sun. The system includes a smaller,
dimmer star called Proxima Centauri.
With a "year" that corresponds to 3.2 Earth days, the newfound
planet is too close to the star to be habitable, notes Xavier
Dumusque, a PhD student in astrophysics at the University of Porto
in Portugal. He led the team reporting the discovery in Thursday's
issue of the journal Nature.
The planet is gravitationally bound to the star in such a way
that it presents the same face to Alpha Centauri B all the time.
This sets up temperatures on the day side that could top 2,200
degrees Fahrenheit, melting rock a sharp contrast with the night
side, perpetually facing the cold of space.
Still, researchers point out that rocky planets tend to have
Evidence from 17 years of hunting planets, especially evidence
that NASA's Kepler spacecraft is amassing, "shows us where there's
one rocky planet, there's more," says Debra Fischer, a Yale
University astronomer who has been deeply involved in hunting for
extrasolar planets for most of this period.
Snagging a rocky planet with an Earth-like mass one solar system
over from ours suggests that "it's a good bet there are other
planets there as well," she adds, including planets orbiting Alpha
Detecting an Earth-mass, rocky planet in the habitable zone of
either star will be extremely difficult. The notion that one of
these lies a cosmically scant 4 light-years away remains
speculation, but "it is not a crazy speculation anymore," says Dr.
Fischer, who was not part of the research team reporting the
The team, which included 11 researchers from Switzerland,
Portugal, and France, used the European Southern Observatory's 3.6-
meter telescope high in the Chilean desert.
The researchers observed the system on and off for four years
using an approach that measures the slight to-and-fro tug a planet
imparts to its host star as the planet orbits. Using a highly stable
spectrograph bolted to the back of the telescope, the team detected
this movement as subtle changes in the star's spectrum which
shifted toward red when the planet tugged the star away from Earth,
and to blue when it pulled the star toward observers.
The effect was tiny, amounting to a change in the stars velocity
of about 1 mile an hour as the planet tugged it back and forth. …