[meteorite-list] Early Mercury Impact Showered Earth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Apr 5 16:23:21 2006
Message-ID: <200604051804.k35I4RM18513_at_zagami.jpl.nasa.gov>

http://www.spacedaily.com/reports/Early_Mercury_Impact_Showered_Earth.html

Early Mercury Impact Showered Earth
SpaceDaily
April 5, 2006

Leicester, England (SPX) - New computer simulations of Mercury's formation
show some of the resulting ejected material ended up on Earth and Venus. The
simulations, which track the material's path over several million years, also
shed light on why Mercury is denser than expected.

Scientists at University of Bern, Switzerland, produced the simulations,
which depict the fate of material blasted out into space when a large
proto-planet collided with a giant asteroid about 4.5 billion years ago,
in the early years of the solar system.

"Mercury is an unusually dense planet, which suggests that it contains
far more metal than would be expected for a planet of its size," said
team leader Jonti Horner, who presented the research at a meeting of the
Royal Astronomical Society.

"We think that Mercury was created from a larger parent body that was
involved in a catastrophic collision, but until these simulations we
were not sure why so little of the planet's outer layers were
re-accreted following the impact."

To solve the problem, the team ran two sets of large-scale computer
simulations. The first examined the behavior of the material in both the
proto-planet and the incoming asteroid. The simulations were among the
most detailed to date, following a huge number of particles and
realistically modeling the behavior of different materials inside the
two bodies.

At the end of the first simulations, a dense Mercury-like body remained,
along with a large swathe of rapidly escaping debris. The trajectories
of the ejected particles were then fed in to a second set of simulations
that followed the motion of the debris for several million years.

A second simulation tracked the ejected particles until they landed on a
planet, were thrown into interstellar space, or fell into the Sun. The
results revealed how much material would have fallen back onto Mercury
and allowed the researchers to investigate ways that debris is cleared
within the solar system.

The group found that the fate of the debris depended on where Mercury
was hit, in terms of its orbital position and the angle of the
collision. Prevailing gravitational theory suggested a large fraction of
the debris eventually would fall back onto the planet, but the
simulations showed it would take up to 4-million years for 50 percent of
the ejecta to return to Mercury, enough time for much of it to be
carried away by solar radiation.

This explains why Mercury retained a much smaller proportion than
expected of the material in its outer layers, Horner explained. He said
the simulations also showed a small fraction of the ejected material
made its way to Venus and Earth - a finding that illustrates how easily
material can be transferred among the inner planets.

Given the amount of material that would have been ejected in such a
catastrophe, Horner said, Earth could contain as much as 16 quadrillion
tons of proto-Mercury particles.

Related Links
RAS 2006 <http://www.nam2006.le.ac.uk/index.shtml>
Royal Astronomical Society <http://www.ras.org.uk/>
Received on Wed 05 Apr 2006 02:04:27 PM PDT