3 planets found around distant star
Discovery raises hopes
for solar systems like our own
By Alan Boyle
WASHINGTON, April 15 -
Building on 11 years of observations,
astronomers say three giant
planets have been detected around a
sunlike star 265 trillion
miles away - representing the first planetary
system that scientists think
could be like our own.
THE TRIPLE DETECTION, announced Thursday by a team of
adds new glimmers of hope to the search for
Earthlike planets and perhaps
even extraterrestrial life. It firms up the
argument that these worlds
are indeed planets rather than brown dwarfs
or captured stars. But it
also poses new puzzles.
"Today, with the discovery of the first planetary system beyond our
own, we are witnessing the
emergence of a new era in human exploration,"
declared Geoffrey Marcy,
an astronomer at San Francisco State University
and one of the system's
discoverers. Just as past cultures looked from
their own lands across seas
and skies, earthlings were now beginning "a
reconnaissance, if you will,
of planets around other stars," he said.
Marcy and his longtime colleague in the search for extrasolar
planets, R. Paul Butler
of the Anglo-Australian Observatory, detected the
first planet around Upsilon
Andromedae in 1996, using what has become
a standard method: They
tracked a pattern of Doppler shifts in the
spectrum of light from the
star, which hints at a wobble caused by the gravitational pull of the circling
planet. About 20 distant worlds have been
detected in this manner.
In the case of Upsilon Andromedae, there was an extra wobble, even
after the first planet's
gravitational pull was taken into effect. Butler, Marcy and other researchers
from San Francisco State, the Harvard-Smithsonian
Center for Astrophysics
and the High Altitude Observatory in Boulder,
Col., determined that
the extra wobble could only be explained by the
presence of two additional
planets. A computer simulation confirmed that
the orbits could be stable.
The researchers said they have submitted a paper on the subject to
the Astrophysical Journal,
drawing on observations made from the Lick
Observatory in California
and the Whipple Observatory in Arizona
FEWER DOUBTS, MORE HOPES
Some skeptics have wondered whether the solitary objects
detected using the Doppler
method might actually be brown dwarfs or
failed stars rather than
planets. But the fact that three such objects were
detected circling the same
star should ease that second-guessing, said
Charles Beichman, chief
scientist for the Origins program at NASA's Jet
"It's just so spectacular, because in science we say, 'Well, we think
it's like this.' But there
is no substitute for really demonstrating that
you're right," he told MSNBC.
The researchers said the new findings suggest that planetary
systems like our own are
abundant among the 200 billion stars in our
galaxy alone. Butler said
this was just the start of what he expected
would become a huge database
of distant solar systems.
"Maybe what we have here is a Rosetta Stone that will eventually
explain how these planets
are formed," he said.
Upsilon Andromedae is 44 light-years away, with each light-year
equal to about 6 trillion
miles. It is in the same class as our sun, roughly
two-thirds as old, and is
visible to the naked eye.
The innermost of the three planets was the first one detected: It's
at least three-quarters
the mass of Jupiter and completes an orbit every
4.6 Earth days, circling
only 6 million miles away from the star.
That would make the innermost planet far too hot to support life. But
the middle planet, with
at least twice the mass of Jupiter, is about as far
away as Venus is from our
own sun, following a 242-day elliptical orbit.
Under the right conditions,
Beichman figures the temperature on a moon
of that planet could vary
between 60 and 140 degrees Fahrenheit (15 to 60
degrees C), with the potential
for liquid water. "That's not bad," he said.
The outermost planet is at least four times as massive as Jupiter
and completes one orbit
every 3.5 to four years, at an average distance
of about 250 million miles.
The temperature there could be a chilly 112
degrees below zero (minus
80 degrees C), Beichman said.
Planetary scientists once thought such giant planets had to form
relatively far out from
their parent star, but the researchers said these
three giants must have either
formed closer in or migrated toward the
center in a game of planetary