[meteorite-list] Diamond Factory: New View of Our Solar System's Youth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:00:06 2004
Message-ID: <200207111708.KAA03605_at_zagami.jpl.nasa.gov>

http://space.com/scienceastronomy/nano_diamonds_020710.html

Diamond Factory: New View of Our Solar System's Youth
By Robert Roy Britt
space.com
10 July 2002

Somewhere in space natural factories churn out uncountable quantities of
tiny diamonds, each thousands of times smaller than a pinhead. Scientists
have long thought they were ancient products of stellar explosions that
occurred before our Sun was born. But new evidence suggests our own solar
system may have once been a diamond factory.

The new idea, strangely enough, is the result of a sky-mining effort that
yielded almost nothing.

Nanodiamonds are said to be the most common type of dust grain in space.
Astronomers suspect they form in the outflows of stellar explosions called
supernovae. Past studies have found them in meteorites -- bits of asteroids
that fell to Earth. Embedded within some of the nanodiamonds is a gas called
xenon, which is used to date the bits of material to an era prior to the
formation of the solar system 4.6 billion years ago.

If the nanodiamonds are indeed "pre solar," then they -- and the meteorites
that house them -- are valuable carriers of information about the
environment around our Sun before and during its formation.

But the dating technique is ambiguous, researchers say.

One way to test the idea is to look for nanodiamonds in comets, which formed
farther from the Sun than did asteroids and so should contain even more of
the miniature structures because they would have been built from a higher
percentage of pristine material that was less affected by the Sun. But until
NASA's Stardust spacecraft brings back material from a comet in 2006,
scientists can't directly examine material from any of these frozen objects.

So John Bradley of the Georgia Institute of Technology and his colleagues
did the next best thing. They studied interplanetary dust particles
collected in the stratosphere, the outermost reaches of Earth's atmosphere.
Based on the speeds and locations of the particles, they are thought to have
been left behind by comets that previously rounded the Sun. (As a comet
nears the Sun, dust and ice boil off, leaving behind a trail of debris.
Earth passes through these trails, sometimes creating meteor showers.)

Nanodiamonds were "absent or very depleted" in the cometary dust grains, the
researchers will report in the July 11 issue of the journal Nature.

Not until Stardust returns will scientists be able to say for sure if the
new results represent the composition of comets in general, Bradley told
SPACE.com. But if his team's study is on track, it would have "profound
implications" on theories of how the solar system formed.

"If [nanodiamonds] do not exist in comets then it is likely that most or all
of them formed in the inner solar system," Bradley said. And that would mean
they did not form prior to the development of the Sun, and that nanodiamonds
don't simply waft through space and get caught up in solar system formation
and emerge unscathed.

There is other evidence to back this scenario.

A recent study appearing in the journal Astronomy & Astrophysics found
evidence for nanodiamonds in a disk of material surrounding a newborn star
called HD 97048. The disk is thought to be similar to one that circled our
Sun in its early years and out of which the planets, comets and asteroids
formed. The study concluded that the diamonds had likely formed in the disk
around HD 97048, not before its creation.

Another possible explanation for the apparent lack of nanodiamonds in
comets, Bradley and his colleagues say, is that nanodiamonds found in
meteorites did indeed form prior to the solar system, but that they simply
didn't exist out where comets were created. This would challenge prevailing
views of how material moved around in the disk of gas and dust circling the
young Sun, they say.
Received on Thu 11 Jul 2002 01:08:12 PM PDT