Models Show One Nearby Star System Could Host Earth-Like Planet

EXTRASOLAR PLANET EARTH HABITABLE JUPITER TERRESTRIAL
Contact Information
Available for logged-in reporters only
Description
Researchers running computer simulations for four nearby systems that
contain giant planets about the size of Jupiter have found one that
could have formed an Earth-like planet with the right conditions to
support life.

Newswise — The steady discovery of giant planets orbiting stars other
than our sun has heightened speculation that there could be Earth-type
worlds in nearby planetary systems capable of sustaining life. Now
researchers running computer simulations for four nearby systems that
contain giant planets about the size of Jupiter have found one that
could have formed an Earth-like planet with the right conditions to
support life.

A second system is likely to have a belt of rocky bodies the size of
Mars or smaller. The other two, the models show, do not have the proper
conditions to form an Earth-size planet. Each system lies within 250
light years of Earth (a light year is about 5.88 trillion miles).
Astronomers already have found evidence that each system contains at
least two giant planets about the mass of Jupiter, which have migrated
close to their stars, perhaps as close as Mercury is to the sun.

For each of the four systems, the researchers conducted 10 computerized
simulations that placed small planet embryos, or protoplanets, in the
system to see if they are able to gather more material and form a true
planet the size of Earth. Each simulation assumed the same conditions in
the planetary system except that the position and mass of each
protoplanet was altered slightly, said Sean Raymond, a postdoctoral
researcher at the University of Colorado, who took part in the work
while he was an astronomy doctoral student at the University of
Washington.

Raymond is lead author of a paper describing the research published in
June in the Astrophysical Journal. Co-authors are Rory Barnes, a
postdoctoral researcher at the University of Arizona who also took part
in the work while a UW astronomy doctoral student, and Nathan Kaib, a UW
doctoral student in astronomy. The work was funded by the National
Aeronautics and Space Administration, NASA's Astrobiology Institute and
the National Science Foundation.

"It's exciting that our models show a habitable planet, a planet with
mass, temperature and water content similar to Earth's, could have
formed in one of the first extrasolar multi-planet systems detected,"
Barnes said.
Recent studies show many known extrasolar planetary systems have regions
stable enough to support planets ranging from the mass of Earth to that
of Saturn. The UW models tested planet formation in systems called 55
Cancri, HD 38529, HD 37124 and HD 74156. The researchers assumed the
systems are complete and the orbits of their giant planets are well
established. They also assumed conditions that might allow formation of
small bodies that could develop into rocky, Earth-like planets.

In the models, the scientists placed moon-sized planet embryos between
giant planets and allowed them to evolve for 100 million years. With
those assumptions, they found terrestrial planets formed readily in 55
Cancri, sometimes with substantial water and orbits in the system's
habitable zone. They found HD 38529 is likely to support an asteroid
belt and Mars-sized or smaller bodies but no notable terrestrial
planets. No planets formed in HD 37124 and HD 74156.

"What surprised me the most was to see the system that only formed
planets the size of Mars or smaller," Raymond said. "Anything that grew
too big would be unstable, so there was an accumulation of a lot of
smaller protoplanets maybe one-tenth the size of Earth."
It was significant, Kaib said, that the models showed conditions could
remain stable enough for 100 million years so that a planetary embryo
would have a chance to gather more substance and develop into a body the
size of the moon or Mars. "In our early system, that's probably what our
inner solar system looked like, with hundreds of bodies that size," he
said.

Extrasolar planets have been discovered with increasing frequency in
recent years because of techniques that detect giant planets by their
gravitational effect on their parent stars. It is uncertain how the
giant planets evolve, but they are thought to form far away from their
host stars and then migrate inward, pushed by the gas discs from which
they formed. If the migration occurs late in the system's development,
the giant planets might destroy most of the materials needed to build
Earth-like planets, Raymond said. He noted that while the presence of
giant planets is fairly well established, it will be some time before it
is possible to detect much smaller Earth-sized planets around other
stars.

For another recent paper, Raymond ran more than 450 computer simulations
to map giant planet orbits that allow Earth-like planets to form. If a
giant planet is too close it will prevent rocky material from amassing
into an Earth-sized planet. That study showed that only about 5 percent
of the known giant-planet systems are likely to have Earth-like planets.

But because of long observation times and sensitive equipment needed to
detect planets the size of Saturn and Jupiter, it is possible there
could be many planetary systems such as ours in this galaxy, he said.