A new planet-hunting technique has detected
the most Earth-like planet yet around a star other than our sun,
raising hopes of finding a space rock that might support life.
"This is an important breakthrough in the quest to answer the
question ‘Are we alone?’" said Michael Turner of the National Science
Foundation.
"The team has discovered the most Earth-like planet
yet, and more importantly, has demonstrated the power of a new
technique that is sensitive to detecting habitable planets," Turner
said in a statement.
In the last decade, astronomers have
detected more than 160 planets orbiting stars outside our solar system.
The vast majority of these have been gas giant planets like Jupiter,
which are hostile to life as it is known on Earth.
But an
international team has detected a cold planet about 5-1/2 times more
massive than Earth — still small enough to be considered Earth-like –
orbiting a star about 20,000 light-years away in the constellation
Sagittarius (The Archer), close to the center of the Milky Way.
A light-year is about 6 trillion miles (10 trillion km), the distance light travels in a year.
To find this new planet — named OGLE-2005-BLG-390Lb — the team used a technique called gravitational microlensing.
This
method uses a network of telescopes to watch for changes in light
coming from distant stars. If another star passes between a distant
star and a telescope on Earth, the gravity of the intervening star acts
like a lens and magnifies the incoming light.
When a planet is
circling the closer star, the planet’s gravity can add its own
signature to the light, the scientists said in research being published
in the current edition of the journal Nature.
This kind of light
signature was observed on July 11 by a group of telescopes
participating in a project known as OGLE, short for Optical
Gravitational Lensing Experiment, which sees more than 500 microlensing
events each year.
At first, OGLE scientists did not know that a planet was responsible for the change in the light.
They
went to two other groups of telescope-using scientists, RoboNet and
PLANET (Probing Lensing Anomalies NETwork), who eventually confirmed
the presences of a previously unknown planet.
Astronomers have
been discovering so-called extrasolar planets for the last decade, but
most have used a method that looks for a characteristic wobble in stars
caused by the unseen planets that orbit around them. This technique has
been successful in finding Jupiter-type planets but few with Earth’s
mass.
However, the microlensing technique may hold promise for
detecting more planets like our own, in the habitable zone neither too
torridly close nor frigidly far from the stars they orbit, said David
Bennett of the University of Notre Dame in Indiana, a member of the
PLANET team.
"The main advantage (of microlensing) is the signals
for low-mass planets: they’re not weak signals, they’re just rare,"
Bennett said by telephone. "If there happens to be a good alignment
between a foreground star with its planet and the background source
star, then you’re able to detect that planet."