[meteorite-list] All planets are born in killer environments

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Sun, 10 Aug 2008 23:53:46 -0400
Message-ID: <9odv94hgl4njviak6f7od3845d875hsrmg_at_4ax.com>

http://www.msnbc.msn.com/id/26077142/

All planets are born in killer environments

New sim shows planetary formation resembles a violent wrestling match

By Jeremy Hsu
Space.com

updated 5:44 p.m. ET, Thurs., Aug. 7, 2008

Our solar system emerged in surprisingly good order from the violence of
planetary creation, according to a new simulation.

Researchers found that planetary formation in the first few million years often
resembles a violent wrestling match among hungry siblings, with planets fighting
to feed on gas and dust while pulling at each other with gravitational arms.

"There's massive bodies competing with each other and flinging each other
around," said Edward Thommes, a physicist at the University of Guelph in Canada,
lead author on the new research published in Friday's issue of the journal
Science.

The simulation traces the creation of a planetary system from almost beginning
to end, for the first time, and suggests that our solar system started with just
the right mass to become a relatively orderly place in the universe.

"You have to have the conditions just right," Thommes told Space.com. "They have
to be in a fairly narrow range."

Thommes and his former colleagues at Northwestern University ran the simulation
through over 100 scenarios to see how gas giants formed from the gas disks that
surrounded young stars. Newborn planets typically seemed to get pushed toward
the central star by the gas disk remnant surrounding them.

"The same disk from which they're born is also trying to kill them," Thommes
said.

Too much starting mass in the disk results in a swarm of gas giants crowding
into the central star. However, too little mass produces nothing bigger than
Neptunelike ice giants.

The tussle among gas giants can typically lead to loopy elliptical orbits.
Sometimes a gas giant even acts as a slingshot to throw a sibling into deep
space.

By comparison, our solar system's gas giants ? Saturn and Jupiter ? have nearly
circular orbits that suggest less violent interaction. The two planets also
appear to have stayed close to where they grew up, instead of migrating into the
sun.

"They never really got into each other's face, so to speak," Thommes said. "They
kept their personal space."

The simulated planetary systems mostly line up with observations of more than
300 exoplanets discovered so far. But Thommes cautioned that the observed
exoplanets represent those that are relatively easiest to find, or "a filtered
sample" of what astronomers can see.

The researchers chose to sacrifice some detail in their simulation in order to
model planetary systems from start to finish. They hope to extend their hybrid
model approach so that they can eventually model planets spiraling all the way
into the central star. Currently, the simulation cannot track such planets
beyond a certain point.

An outside essay accompanying the Science paper and written by John Papaloizou,
an astrophysicist at the University of Cambridge in Britain, calls the new
simulation "compelling" and says that it achieves "reasonable success" in
modeling what astronomers have observed.


Papaloizou pointed out that some simulated planetary orbits do not match up with
the usual equatorial plane of star systems, something that astronomers have not
seen in exoplanetary systems so far. However, he also adds that current
knowledge of exoplanetary systems remains limited.

For his part, Thommes remained confident that our solar system was uniquely
quiet, especially considering the birthing process.

"What our solar system seems to represent in all of this is a peaceful and quiet
form of this process," Thommes said.
Received on Sun 10 Aug 2008 11:53:46 PM PDT