**Stardust Up Close**

by Patrick L. Barry and Dr. Tony Phillips

Like discarded lumber and broken bricks around a construction site,
comets scattered at the edge of our solar system are left-over bits from
the \"construction\" of our solar system.

Studying comets, then, can help scientists understand how our solar
system formed, and how it gave rise to a life-bearing planet like Earth.

But comets have long been frustratingly out of reach \-- until recently.
In January 2004 NASA\'s Stardust probe made a fly-by of the comet Wild 2
(pronounced \"vilt\"). This fly-by captured some of the best images and
data on comets yet \... and the most surprising.

Scientists had thought that comets were basically \"rubble piles\" of
ice and dust \-- leftover \"construction materials\" held together by
the comet\'s feeble gravity. But that\'s not what Stardust found. Photos
of Wild 2 reveal a bizarre landscape of odd-shaped craters, tall cliffs,
and overhangs. The comet looks like an alien world in miniature, not
construction debris. To support these shapes against the pull of
gravity, the comet must have a different consistency than scientists
thought:

\"Now we think the comet\'s surface might have a texture like
freeze-dried ice cream, so-called \'astronaut ice cream\': It\'s solid
and can assume odd, gravity-defying shapes, but it\'s basically soft and
crumbles easily,\" says Donald Brownlee of the University of Washington,
principal investigator for Stardust.

Scientists are currently assembling a 3-D computer model of this surface
from the photos that Stardust took. Those photos show the sunlit side of
the comet from many angles, so its 3-dimensional shape can be inferred
by analyzing the images. The result will be a \"virtual comet\" that
scientists can examine from any angle. They can even perform a virtual
fly-by. Using this 3-D model to study the comet\'s shape in detail, the
scientists will learn a lot about the material from which the comet is
made: how strong or dense or brittle it is, for example.

Soon, the Stardust team will get their hands on some of that material.
In January 2006, a capsule from Stardust will parachute down to Earth
carrying samples of comet dust captured during the flyby. Once
scientists get these tiny grains under their microscopes, they\'ll get
their first glimpse at the primordial makings of the solar system.

It\'s heading our way: ancient, hard-won, possibly surprising and
definitely precious dust from the construction zone.

Find out more about the Stardust mission at stardust.jpl.nasa.gov. Kids
can read about comets, play the "Tails of Wonder" game about comets, and
hear a rhyming story about aerogel at
<http://spaceplace.nasa.gov/en/kids/stardust/>.

*This article was provided by the Jet Propulsion Laboratory, California
Institute of Technology, under a contract with the National Aeronautics
and Space Administration.*

![](media/image1.jpeg){width="3.5305555555555554in" height="5.2875in"}

*The Stardust spacecraft used a grid holding aerogel to capture dust
particles from comet Wild 2. In this test, high velocity dust particles
are stopped unharmed at the end of cone shaped tracks in a sample of
aerogel*

Note to editor: This image can be downloaded from:

<http://spaceplace.nasa.gov/astro_clubs/aerogel_tracks.jpg>