January 2005
Stardust Up Close
By Patrick L. Barry and Dr. Tony Fisher
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
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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. |
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
http://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.