Distant Planet Spotted Around the Bend
A new technique using distorted light waves should help astronomers
identify Earth-sized bodies.
By Thomas H. Maugh II,
Times Staff Writer
April 16, 2004
Astronomers have for the first time used the bending of light waves from
a star to identify a planet 17,000 light-years away, an achievement that
could set the stage for the discovery of more extrasolar planets,
especially smaller planets similar in size to Earth.
Researchers have so far identified more than 100 extrasolar planets by
observing slight wobbles in a star's trajectory caused by a planet
circling it or by observing small changes in a star's brightness when a
planet passes in front of it.
But those methods work only for planets larger than Jupiter, and most of
the planets discovered so far orbit very close to their stars —
indicating that the planetary systems are not very much like our own.
Although the planet discovered using the new technique, called
gravitational microlensing, is about the size of Jupiter, the method
should work equally well with smaller planets, researchers said.
Furthermore, the newly discovered planet, in the constellation
Sagittarius, orbits its star at a distance of about three astronomical
units (one AU equals the distance from Earth to the sun), and that star
is a red dwarf similar to our sun.
The fact that the newly discovered planet orbits its star at such a
distance means there could be smaller planets, more like Earth, Venus and
Mars, orbiting it more closely, said NASA's Philippe Crane, who is in
charge of the search for such planets.
The new technique relies on the fact that powerful gravitational fields
can bend light rays, a phenomenon first predicted by Albert Einstein.
When a relatively nearby star passes between an earthbound telescope and
a more distant star, its gravity acts like a telescopic lens, bending and
focusing light from the distant star so that it appears much brighter
than it otherwise would.
About 13 years ago, astronomer Bohdan Paczynski of Princeton University
and his student Shude Mao suggested that this microlensing capability
could be used to find extrasolar planets.
A smaller object, such as a planet, would have a similar brightening
effect. The increase in brightness would be smaller, though still easily
"I'm thrilled and delighted to see that old idea come true," Paczynski
said Thursday in a telephone news conference announcing the finding. The
report will be published in the May 10 issue of Astrophysical Journal
The discovery was made jointly by two international teams that use large
digital detectors attached to telescopes to monitor as many as 200
million stars at a time, looking for changes in brightness.
The two groups together observe about 570 such events each year,
according to astronomer Ian Bond of the University of Edinburgh in
Scotland, who led the team reporting the new planet. Virtually all of
those events, however, occur when a single star acts as a gravitational
lens for a second single star.
Last July, however, the team observed an event in which the brightness of
the observed star increased twice over a period of about 40 days,
indicating the presence of two objects in the system acting as the lens.
Mathematical calculations indicted that the second object had only 0.4%
of the mass of the star and must therefore be a planet, and about 1
1/2times the size of Jupiter.
Obtaining the proper astronomical alignment to use gravitational
microlensing is a very rare event, Paczynski noted, occurring less than
once in every 100 million observations. But the groups are looking at so
many stars that he believes they will find many more planets.
"The chances are good we will discover another planet within the next
half-year," he said.