[meteorite-list] Wandering Jupiter Could Have Swept Inner Solar System Clean

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 22 Mar 2016 15:54:21 -0700 (PDT)
Message-ID: <201603222254.u2MMsLb4023404_at_zagami.jpl.nasa.gov>

https://www.sciencenews.org/article/wandering-jupiter-could-have-swept-inner-solar-system-clean

Wandering Jupiter could have swept inner solar system clean

On its way out, infant planet left only enough debris for four small planets,
simulation suggests

By Christopher Crockett
Science News
March 15, 2016

A wandering baby Jupiter could help explain why there are no planets closer
to the sun than Mercury and why the innermost planet is so tiny, a new
study suggests.

Jupiter's core might have formed close to the sun and then meandered
through the rocky planet construction zone. As the infant Jupiter moved,
it would have absorbed some planet-building material while kicking out
the rest. This would have starved the inner planets - Mercury, Venus,
Earth and Mars - of raw materials, keeping them small and preventing
any other planets from forming close to the sun, say planetary scientist
Sean Raymond and colleagues online March 5 in Monthly Notices of the Royal
Astronomical Society.

"When I first came up with it, I thought it was ridiculous," says
Raymond, of the Laboratory of Astrophysics of Bordeaux in Floirac, France.
"This model is kind of crazy, but it holds up."

Rocky planets snuggled up to their suns are common in our galaxy. Many
systems discovered by NASA's Kepler space telescope have multiple planets
- several larger than Earth - crammed into orbits smaller than Mercury's.
Though Kepler is biased toward finding scrunched-up solar systems, researchers
wonder why there is a large gap between the sun and Mercury.

Scientists suspect that the inner planets of our solar system formed 4.6
billion years ago from a belt of debris that stretched between the current
orbits of Venus and Earth. Mercury and Mars were built out of material
along the edges of this belt, which explains why they are relatively small.
Jupiter, traditionally thought to have formed much farther out, gets the
blame for creating the belt's outer edge. What shaped the inner edge
has remained difficult to explain (SN Online: 3/23/15).

Raymond and colleagues ran computer simulations to see what would happen
to the inner solar system if a body with three times the mass of Earth
started inside Mercury's orbit and then migrated away from the sun.
They found that if the interloper didn't move too fast or too slow,
it would sweep clean the innermost parts of the disk of gas and dust that
encircled the young sun and leave just enough material to form the rocky
planets.

Raymond and colleagues also discovered that young Jupiter could have corralled
enough debris to form a second core - one that got nudged away from
the sun as Jupiter migrated. This second core could be the seed from
which Saturn grew, the researchers suggest. Jupiter's gravity could
have dragged debris to the asteroid belt, too. Raymond says that might
explain the origin of iron meteorites, which some researchers argue should
have formed relatively close to the sun.

Jupiter plowing through the inner solar system sounds plausible, says
Sourav Chatterjee, an astrophysicist at Northwestern University in Evanston,
Ill. "But there are several ways this can go wrong."

Building a giant planet core inside the orbit of Mercury is not hard,
he says. Pebbles and boulders in the nascent solar system probably drifted
inward. They could have piled up close to the sun where solar magnetic
fields created turbulence that trapped infalling material. If just a fraction
of this debris stuck together, a rocky orb a few times as massive as Earth
could form.

Having proto-Jupiter wander to the outer solar system, however, is asking
a lot, says Chatterjee. Gravitational interactions with spiral waves in
the disk that surrounded the sun can propel a newborn planet either inward
or outward. But how fast, how far and in which direction the planet travels
depends on properties such as disk temperature and density, which Raymond
and colleagues readily acknowledge. Their simulations assume and simplify
disk characteristics to see if building the solar system inside-out is
even plausible.

"We're building up a logical chain that shows [this idea] is not completely
crazy," Raymond says. "We're not saying it happened. Just if it
happened, what would it do?"
Received on Tue 22 Mar 2016 06:54:21 PM PDT