by Playfuls Staff |
8th September 2006
More than one-third of the giant planet systems recently
detected outside Earth's solar system may harbor Earth-like planets, many
covered in deep oceans with potential for life, according to a new study led by
the University of Colorado at Boulder
and Pennsylvania State University.
[more]
The study focuses on a type of planetary system unlike our
solar system that contains gas giants known as "Hot Jupiters"
orbiting extremely close to their parent stars - even closer than Mercury to
our sun, said CU-Boulder researcher Sean Raymond. Such gas giants are believed
to have migrated inward toward their parent stars as the planetary systems were
forming, disrupting the space environment and triggering the formation of
ocean-covered, Earth-like planets in a "habitable zone" conducive to
the evolution of life, according to the new study.
"Exotic Earths: Forming Habitable Worlds with Giant
Planet Migration" was published in the Sept. 8 issue of Science and
authored by Raymond, Avi Mandell of both Penn State and Goddard Space Flight
Center in Greenbelt, Md., and Steinn Sigurdsonn of NASA's Goddard Center.
The study indicates Hot Jupiters push and pull
proto-planetary disk material during their journeys, flinging rocky debris
outward where it is likely to coalesce into Earth-like planets, said Raymond.
At the same time, turbulent forces from the dense surrounding gas slow down the
orbits of small, icy bodies in the outer reaches of the disk, causing them to
spiral inward and deliver water to the fledgling planets. Such planets may
eventually host oceans several miles deep, according to the study.
"These gas giants cause quite a ruckus," said
Raymond of CU-Boulder's Laboratory for Atmospheric and Space Physics. "We
now think there is a new class of ocean-covered, and possibly habitable,
planets in solar systems unlike our own."
Scientists had previously assumed that as Hot Jupiters
plowed through proto-planetary material on their inward migrations toward
parent stars, all the surrounding material would be "vacuumed up" or
ejected from the system, he said. "The new models indicate these early
ideas were probably wrong," said Raymond.
The research team ran exhaustive simulations lasting more
than eight months each on more than a dozen desktop computers, starting with
proto-planetary disks containing more than 1,000 moon-sized, rocky and icy
bodies. The initial conditions for each computer model were based on current
theories of how planets form in our own solar system and simulated about 200
million years of planetary evolution.
The team concluded that about one of every three known
planetary systems could have evolved as-yet-undetected Earth-like planets in
so-called habitable zones like the one Earth is in, he said. A whopping 40
percent of the 200 or so known planets around other stars are Hot Jupiters,
although the percentage probably will decrease as more distant planets are
discovered, said Raymond.
In addition to Earth-like planets that form in habitable
zones outside Hot Jupiters, the simulations showed some rocky planets known as
"Hot Earths" often form inside the orbits of Hot Jupiters, said
Raymond. A Hot Earth, with a radius twice that of our own Earth, was discovered
in 2005 in a nearby star system orbiting just 2 million miles from its parent
star by a team led by University of California, Berkeley, planetary scientist
Geoffrey Marcy.
The new simulations showed both Hot Earths and Earth-like
planets in habitable zones formed with large amounts of water, up to 100 times
the water present on Earth today, he said. The models indicate such water-rich
planets would probably contain a lower percentage of iron - which may be
important for the evolution and possible oxygenation of evolving atmospheres -
than Earth, he said.
According to the team's simulations, Hot Earths can form
astoundingly fast, in just 100,000 years or so. Earth-like planets in habitable
zones form much more slowly, taking up to 200 million years, said Raymond.
Geologists believe Earth took about 30 million years to 50 million years to
fully form.
"I think there are definitely habitable planets out
there," said Raymond. "But any life on these planets could be very
different from ours. There are a lot of evolutionary steps in between the
formation of such planets in other systems and the presence of life forms
looking back at us."
The new research effort may allow planet hunters to
determine "rough limits" indicating where to search for habitable
planets in known systems of giant planets, according to the team, whose
research was funded by NASA's Astrobiology Institute headquartered at the NASA Ames Research Center
in Moffett Field, Calif.
"Upcoming space missions such as NASA's Kepler and
Terrestrial Planet finder and ESA's COROT and Darwin will discover and
eventually characterize Earth-like planets around other stars," wrote the
authors in Science. ""We predict that a significant fraction of
systems with close-in giant planets will be found to have a Hot Earth or
potentially habitable, water-rich planets on stable orbits in the Habitable
Zone."
Image Credit: Sean Raymond, CU-Boulder, using images from
NASA
