[meteorite-list] #2 Study: Earthlike planets may be common

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Mon Sep 11 00:07:20 2006
Message-ID: <002201c6d547$2c9c4170$5f5ae146_at_ATARIENGINE>

Hi,

    The same scientist that published this month the study,
which says that close Jupiters allow terrestrial planets
with lots of water, also published in May, 2006 a study that
says what seems at first to be saying the exact opposite:
http://arxiv.org/abs/astro-ph/0605136

    This study eliminates terrestrial water-rich worlds only
when the Jupiters orbit between 1.6 AU and 3.5 AU. So
that eliminates such systems (which is most of the extra-
solar planetary systems we've already discovered) as good
candidates for Earth-like water-rich worlds. The two studies
together indicate you can have water-rich Earth-like worlds
with close Jupiters or with far Jupiters, but not with
"in-between" Jupiters.

    I quote from the abstract:
    "We present results of 460 N-body simulations of
terrestrial accretion from a disk of Moon- to Mars-sized
planetary embryos. We systematically vary the orbital
semimajor axis of a Jupiter-mass giant planet between
1.6 and 6 AU, and eccentricity between 0 and 0.4.
We find that for Sun-like stars, giant planets inside
roughly 2.5 AU inhibit the growth of 0.3 Earth-mass
planets in the habitable zone. If planets accrete water
from volatile-rich embryos past 2-2.5 AU, then
water-rich habitable planets can only form in systems
with giant planets beyond 3.5 AU. Giant planets with
significant orbital eccentricities inhibit both accretion
and water delivery. The majority of the current sample
of extra-solar giant planets appears unlikely to form
habitable planets."

    However nice it is to pin these things down, do we
really need a big computer to tell us if Jupiter orbited the
Sun at, say, the distance of Ceres, our planet Earth simply
wouldn't be here? Didn't we know that already?


Sterling K. Webb
-----------------------------------------------------------------
----- Original Message -----
From: "Darren Garrison" <cynapse_at_charter.net>
To: <meteorite-list_at_meteoritecentral.com>
Sent: Friday, September 08, 2006 10:54 AM
Subject: [meteorite-list] Study: Earthlike planets may be common


http://www.cnn.com/2006/TECH/space/09/08/earthlike.planets.reut/index.html

WASHINGTON (Reuters) -- Earthlike planets covered with deep oceans that
could
harbor life may be found in as many as a third of solar systems discovered
outside of our own, U.S. researchers said on Thursday.

These solar systems feature gas giants known as "Hot Jupiters," which orbit
extremely close to their parent stars -- even closer than Mercury to our
sun,
University of Colorado researcher Sean Raymond said.

The close-orbiting gassy planets may help encourage the formations of
smaller,
rocky, Earthlike planets, they reported in the journal Science.

"We now think there is a new class of ocean-covered, and possibly habitable,
planets in solar systems unlike our own," Raymond said in a statement.

The team from Colorado, Penn State University and NASA's Goddard Space
Flight
Center Maryland ran computer simulations of various types of solar systems
forming.

The gas giants may help rocky planets form close to the suns, and may help
pull
in icy bodies that deliver water to the young planets, they found.

"These gas giants cause quite a ruckus," Raymond said.

Water is key to life as humans define it.

"I think there are definitely habitable planets out there," Raymond said.
"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."

As many as 40 percent of the 200 or so known planets around other stars are
Hot
Jupiters, the researchers said.
______________________________________________
Meteorite-list mailing list
Meteorite-list_at_meteoritecentral.com
http://six.pairlist.net/mailman/listinfo/meteorite-list
Received on Sun 10 Sep 2006 10:08:28 PM PDT