[meteorite-list] Magma Oceans Sloshed Across Early Asteroids

[Darren Garrison]

On Wed, 15 Jun 2005 10:37:49 -0700 (PDT), Ron Baalke <baalke at zagami.jpl.nasa.gov> wrote:

>
>http://www.newscientist.com/article.ns?id=dn7522
>
>Magma oceans sloshed across early asteroids
>Jeff Hecht
>New Scientist
>June 15, 2005
>
>Oceans of molten rock, or magma, covered some asteroids in the early
>solar system, reveals a new study of meteorites. But researchers are
>still puzzled over why other asteroids apparently did not melt at all.

Here's a different article on the same paper but giving a different twist-- that the Earth could be
made up largely from asteroids that had already melted, differentiated, and had much of the lighter
crust blasted away before being incorporated into the growing Earth.  Which would give the Earth a
different overall composition than the full "solar composition" (even for non-volitiles).  I don't
know what to think of that, though, because you'd think that that lighter crustal material blasted
off the bigger asteroids that made up the Earth would have ended up becoming part of the Earth
anyway, just not all in one big chunk.



http://www.universetoday.com/am/publish/melted_asteroids.html?1562005

Earth Formed from Melted Asteroids 

Summary - (Jun 15, 2005) Many of the Earth's volcanic rocks might have come from melted asteroids,
according to researchers from the UK's Open University. The scientists have discovered that many
early asteroids were quite volcanic and would have had large magma oceans. These asteroids would
have become layered with lighter rock forming near the surface while denser rocks were deeper
inside. The Earth probably grew from the accumulation of these melted asteroids. 

Full Story -  
The image above is a false color view of the asteroid 951 Gaspra taken by the Galileo spacecraft.
Image credit: NASA/JPL. Click to enlarge. 
Important new research documenting how the Earth formed from melted asteroids 4.5 billion years ago
is published in the 16 June issue of Nature. The paper was written by Dr Richard Greenwood and Dr
Ian Franchi of the Open University’s Planetary and Space Sciences Research Institute (PSSRI). 

"This research is important, Dr Greenwood says, “because it demonstrates that events and processes
on asteroids during the birth of the Solar System determined the present-day composition of our
Earth."

Immediately following the formation of our Solar System 4.5 billion years ago, small planetary
bodies formed, with some melting to produce volcanic and related rocks. The OU researchers analysed
meteorites to see how processes on asteroids may have contributed to the formation of Earth.

In their paper “Widespread magma oceans on asteroidal bodies in the early Solar System” Drs
Greenwood and Franchi show that some asteroids experienced large-scale melting, with the formation
of deep magma oceans. Such melted asteroids would have become layered with lighter rock forming near
the surface, while denser rocks were deeper in the interior. Since large bodies, such as Earth, grew
by incorporation of many such smaller bodies these important results shed new light on the processes
involved in building planets. 

The researchers suggest that in the chaotic, impact-rich environment of the early Solar System,
significant amounts of the outer layers of these melted asteroids would have been removed prior to
becoming part of the growing Earth. This process is a better explanation for the composition of the
Earth than earlier theories which called for large amounts of light elements in the Earth’s dense
core, or unknown precursor materials. The Open University researchers point to recent astronomical
observations which show that these processes are also important in other planetary systems, such as
that around the star Beta Pictoris.