Dynamics of Cats

More than one-third of the giant planet systems recently detected outside our
solar system may harbor Earth-like planets, according to a new study by
scientists associated with NASA's Astrobiology Institute. Many of these planets
may be covered in deep global oceans, with abundant potential for life.

PS: Seed Magazine news story on this

see WaPo's Achenblog for perspective:
Question Authority! Why?

Good BBC article on it here

Actual paper is up on Science's web site now (subscription)

Also Cool paper by Squyres' et al on water on Mars

Click here for hi-res version
© Nahks

The study focuses on planetary systems that contain "Hot Jupiters": gas giant
planets that orbit extremely close to their parent stars -- even closer than
Mercury to our own Sun. Hot Jupiters are believed to have migrated inward
toward their parent stars just 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. Titled "Exotic Earths: Forming Habitable Worlds with Giant
Planet Migration," the Science paper was authored by Dr. Sean Raymond of the
University of Colorado at Boulder, Avi Mandell of Pennsylvania State University
and NASA's Goddard Space Flight Center in Greenbelt, Md., and Dr. Steinn
Sigurdsson of Pennsylvania State University.

Published in the Sept. 8 issue of Science, 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. At the
same time, turbulent forces from the surrounding dense gas slow the small, icy
bodies in the outer reaches of the disk, causing them to spiral inward and
deliver water to the fledgling planets. These planets may eventually host
oceans several miles deep, according to the study.

"These gas giants completely shake up the system as they migrate, but eventually
things settle down," said Mandell. "We now think there is a new class of ocean-
covered and possibly habitable planets in solar systems very different from our
own."

Scientists had previously assumed that as Hot Jupiters plowed through proto-
planetary material on their inward migrations toward their parent stars, all the
surrounding material would be vacuumed up or ejected from the system. "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 from a disk of more than a
thousand rocky and icy protoplanets about the size of the moon. The initial
conditions for each computer model were based on current theories of how planets
formed in our own solar system and simulated about 200 million years of
planetary evolution.

In addition to the Earth-like planets that form in habitable zones outside Hot
Jupiters, the simulations showed some rocky planets known as "Hot Earths" often
form with orbits interior to the orbit of a Hot Jupiter. Evidence of this
phenomenon comes from recent discoveries of similar planets in other star
systems: planets more massive than Earth but much smaller than gas planets
(hence the term "Hot Earth"). These planets would be extremely hot and most
likely uninhabitable.

The new simulations show both Hot Earths and Earth- like planets in habitable
zones form with large amounts of water -- up to 100 times the water present on
Earth today. The models indicate such water-rich planets would likely contain a
lower percentage of iron than Earth, thought by some astrobiologists to be
important for the evolution and possible oxygenation of evolving atmospheres.
According to the team's computer simulations, Hot Earths can form astoundingly
fast -- in just 100,000 years or so, while the Earth-like planets in habitable
zones formed much more slowly, taking up to 100 million years. Geologists
believe Earth took about 30 million 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 lot
evolutionary steps in between the formation of such planets in other systems and
the presence of life forms looking back at us."

The team concluded that approximately 1 out of 3 of the known planetary systems
could have formed as-yet-undetected Earth-like planets in so-called habitable
zones similar to the one that Earth's orbit resides in. "The fraction of known
systems that could have the potential for life may be significantly higher than
we had thought," said Mandell. A whopping 40 percent of the roughly 200 known
extra-solar planets are Hot Jupiters, but this percentage will likely decrease
as more extrasolar planets are detected.

The new collaborative research effort may allow planet hunters to determine
rough limits for where to search for habitable planets in known systems of giant
planets. "We hope other researchers may be able to use our new model to narrow
the list of potential targets in the search for other Earths", Dr. Sigurdsson
said. This will help in upcoming space missions such as NASA's Kepler and
Terrestrial Planet finder and ESA's COROT and Darwin, which hope to discover and
eventually characterize Earth-like planets around other stars, the team writes
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. Suitable targets may be
found in the known giant planet systems."

Surf's Up, Dude