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| Photo: An artist's rendering of a habitable,
Earth-like world, having 8 times the mass of our Earth,
of the sort that we hope to discover with Keck in the
next couple of years. This super-Earth orbits its host
star at the "Goldilocks" distance from its host star so
that the temperature is just right for liquid water and
for life. The artist is a Berkeley student, Suneet Upadhyay.
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Using the W. M. Keck Observatory telescope, Geoff Marcy's research
group has discovered new worlds that orbit other stars. These
are the first planetary systems ever found around other stars.
Marcy's group is finding the first "new worlds" in our universe,
to complement the eight planets that orbit our Sun.
So far Marcy's group has found large planets, the size of Jupiter,
Saturn, and Neptune. Some of these planets are unexpected and
bizarre. Most of them go around their stars in elongated orbits,
not in neat circles like the planets in our Solar System. Some
planets orbit so close to their star that the planets are blow-torched
to thousands of degrees Fahrenheit.
The elongated orbits came as a complete surprise to the members
of Marcy's team. "We are human, and as humans often do, we expected
that other systems would be just like ours: with planets orbiting
their stars in circles," says Marcy.
In fact, only about 10 percent of the 121 exo-solar (outside
our solar system) planets they have discovered to date have
circular orbits. The other 90% have wacky, elongated orbits.
Marcy's team suspects the erratic orbits occur because planets
in these systems are located in close enough proximity to exert
gravitational pulls on one another. This mutual gravitational
pull could be enough to perturb the orbits of both planets:
sending the smaller planet reeling off into space and warping
the orbit of the larger planet to create the kind of elongated
orbits they are observing.
Most of the new worlds Marcy's group has discovered so far are
10 to 1,000 times more massive than our Earth. Over the past
few years the team members have refined their techniques to
enable them to detect smaller and smaller planets. The smallest
planet yet discovered is just 7.5 times the size of Earth, and
this "little guy" is not alone.
The goal for the next year is to find Earth-like planets. These
would be worlds with both a rocky surface and lukewarm temperatures,
allowing life to develop and thrive. The rocky surface allows
water to pool and to pond, providing ideal conditions to support
life.
"The planets we are looking for will be located at the 'Goldilocks'
distance from their sun, or at just the right distance to support
life," says Marcy. "We don't yet have the tools to detect life
itself, but we can identify Earth-like planets."
Marcy started this project back in 1987, when he was a professor
at San Francisco State University. He worked with one of his
students, Paul Butler, who is currently a staff scientist at
the Carnegie Institution of Washington, D.C. The two other team
members are Debra Fischer, from San Francisco State University,
and Steve Vogt, who was Marcy's thesis advisor when he was a
student. Together, the four team members represent three generations
of researchers. "We are like family," says Marcy. The four are
very seldom together, but they communicate virtually on a regular
basis.
The project took a giant stride forward in August 2004, when
the high-resolution spectrometer, "HIRES" was refurbished at
Keck. This $5 million investment, funded in part by NASA and
in part by Keck Observatory, is at the heart of the planet searching
business. This new instrument allows Marcy's team to measure
the Doppler effect, which tells them the speed of stars as they
wobble reflexively in response to their planets pulling on them
gravitationally. The bigger the object or planet exerting the
pull, the greater the wobble of the star.
"The wobble can be likened to a dog owner walking a big dog
on a leash. The bigger the dog, the more the owner is likely
to wobble. In the case of stars, the leash is gravity," explains
Marcy.
This brilliant technique of measuring the Doppler effect of
a star to detect the presence of planets was pioneered by Canadian
scientists working out of Canada France Hawai'i Telescope in
the 1990's. They never discovered any planets, but Marcy's group
has refined the Canadians' techniques and applied much more
powerful technology to the task, such as the HIRES at Keck.
At this point Marcy's group is discovering roughly one planet
per week. Over the next year they are targeting 230 stars located
within 30 light years of Earth and distributed fairly evenly
throughout the night sky - in both the Northern and the Southern
hemispheres. None of these target stars is a binary star, since
the combined gravitational effects of two stars orbiting each
other makes it unlikely that planets with regular orbits will
be present. None of the target stars is too young, because young
stars exhibit flares and sunspots which reduce the likelihood
that planets orbiting these stars could sustain life.
"Every night of the year, we take at least one observation of
each of the 230 target stars from Keck Observatory," states
Marcy. Mauna Kea is an ideal spot for these observations because
from there, it is possible to view much of the sky over the
Southern hemisphere, something astronomers can't do as well
on the U.S. Mainland. At the end of the year Marcy's group will
evaluate their observations to determine which stars exhibit
periodic wobbles as their planets orbit around them.
"We have not detected a single Earth-like planet yet," says
Marcy. "Our Solar System may just be some quirky architecture
that allowed life to occur, but this seems unlikely. In all
of the billions of stars out there, there is probably life somewhere,
likely even intelligent life," he speculates.
Life on other stars is probably made of organic molecules, similar
chemically to life on Earth. Long carbon-based molecules, such
as amino acids and proteins, are the most likely building blocks
of all life. Astronomers see amino acid molecules on comets
and in the gas in between stars.
If Marcy's team does identify Earth-like planets, the next step
will be to point the world's largest radio telescopes and infrared
telescopes at that star system -- hoping to pick up radio or
television signals from any advanced civilizations that might
inhabit that world.
"If we detect such transmissions, this will have tremendous
implications for humankind," says Marcy. "Some people will react
with fear, afraid that Earth will be threatened by extraterrestrial
life. Others will attempt to communicate and seek to establish
a connection. And, once the newness of the discovery wears off,
most of us will continue on with business as usual."
Learn more about the search for exo-solar planets and view a
Catalog of Nearby Exoplanets at www.exoplanets.org.
The Catalog contains 178 planets, all within 200 parsecs of
Earth (a parsec is roughly equivalent to 3.26 light years),
and contains the orbital parameters and masses for each of them.
The Catalog was also published in the July issue of The
Astrophysical Journal.
Read Geoff Marcy's speech,
which he drafted upon acceptance of the 2005
Shaw Prize for Astronomy. The Shaw Prize honors individuals
who have achieved a "significant breakthrough in academic and
scientific research or application, and whose work has resulted
in a positive and profound impact on humankind." 
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