[meteorite-list] Getting your HED examined

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Sat, 14 Apr 2007 22:51:10 -0500
Message-ID: <788323pidsh9nrrism63nldfpvs0dp40bd_at_4ax.com>

http://www.lamonitor.com/articles/2007/04/14/headline_news/news01.txt

GRaND instrument primed for voyage

 
 
ROGER SNODGRASS Monitor Assistant Editor

The Dawn spacecraft, carrying an instrument package from Los Alamos, reached
another milestone this week on a journey to the asteroids. NASA announced that
Dawn arrived at Astrotech Space Operations in Titusville, Fla., at 9 a.m.
Tuesday for final preparations.

Countdown is now 76 days until June 30, when Dawn is set to go up like thunder
on a heavy-lifting version of a Delta II rocket.

"It's particularly sweet for us, in that we had quite a few ups and downs
getting to the point where we are ready to launch," said Tom Prettyman, the lead
scientist for the Los Alamos instrument and a mission co-investigator.

The next step is a 15-mile jaunt down the road to the launch pad, followed by a
3.2 billion-mile expedition to the asteroid belt that lies between Mars and
Jupiter.

The spacecraft will be powered by a pioneering new ion propulsion system that
uses electric fields instead of chemical reactions to achieve a thrust.

Dawn's job is to visit and circle around two contrasting space objects - first,
the asteroid Vesta and second, the dwarf planet Ceres. Vesta is dry and
volcanic. Ceres may harbor ice or water. Vesta is melted, evolved and shaped
like the top of a skull. Ceres is rough and crude, but round.

Vesta, Prettyman said, is an inner-belt body, closer to the sun than Ceres,
which is larger and more in the middle of the asteroid belt.

The difference between them is one of the main points of the mission and partly
why they were chosen as destinations.

"We want to understand how solar nebulae varied with the distance from the sun
and how the planets formed," he said.

Both objects are thought to be very old relics, among the first-formed bodies in
the solar system 4.5 billion years ago. Because they have probably always been
among the biggest chunks of matter in the region, they were the least likely to
be perturbed or swept up by the gas-giant Jupiter. The smallest pieces were
knocked around, broken into pieces and expelled, until only a fraction of the
original main belt asteroid material remains.

An old hypothesis held that asteroids were the remains of a destroyed planet
named Phaeton, but now the main line of inquiry is why the pieces went through a
building and accreting process up to a point but failed to form a planet.

After Dawn gets a gravity boost in a fly-by of Mars in March 2009, it will reach
Vesta in late 2011 and Ceres in early 2015. In both cases, the spacecraft will
survey the situation before beginning a polar orbit and bearing down for closer
inspection. The spacecraft will circle both poles, while the body rotates to
reveal its entire surface.

The LANL instrument, the Gamma Ray and Neutron Detector (GRaND), one of three
science instruments Dawn carries in its payload, comes from a long line of space
instruments the lab has built for NASA missions. It will map the surface of each
asteroid for ratios of rock-forming elements and the telltale hydrogen atoms
that indicate ice or water.

Another goal is to try to pin down Vesta's tantalizing relationship to a class
of meteorites known as HEDs (howardite, eucrite and diogenite) and to try to
determine if any meteorites come from Ceres.

"These are places we've never been before," said Prettyman. "They are intriguing
because they are representatives of planetary embryos."

The mission is managed by the Jet Propulsion Laboratory in Pasadena and involves
scientific partnerships with the German Aerospace Center, the Max Planck
Institute for Solar System Research and the Italian National Institute of
Astrophysics.

Three groups in the labs International Space and Response Division have been
involved in developing and engineering the GRaND and integrating it with the
spacecraft.
Received on Sat 14 Apr 2007 11:51:10 PM PDT