[meteorite-list] Extraterrestrial Capture - Interview with Don Brownlee

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:18:06 2004
Message-ID: <200312312053.MAA28784_at_zagami.jpl.nasa.gov>

http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=742&mode=thread&order=0&thold=0

Extraterrestrial Capture
Astrobiology Magazine
December 31, 2003

In the next few days, a bullet-speed spacecraft called Stardust will pass
through the wispy tail of a comet, capture about an ounce of its delicate
particles, and then begin its return voyage back to Earth. Astrobiology
Magazine talked with Stardust's principal investigator, Professor Don Brownlee,
about the logistics of his forthcoming treasure hunt.

Extraterrestrial Capture

Interview with Don Brownlee

"This is an exciting time," says University of Washington astronomy
professor, Don Brownlee, who is also the principal investigator for NASA's
Stardust mission. Stardust is scheduled to contact a comet on January 2nd,
and return collected dust to Earth in January 2006. It is the first
sample-return mission since Apollo. The spacecraft will fly a near-collision
course within 300 kilometers (200 miles) of the wispy tail of a comet called
Wild 2, while trapping tiny comet particles in a low-density silica material
called aerogel.

To the delight of mission scientists on November 13, the cometary ball of
dirty ice and rock--about as big as three Brooklyn Bridges laid end-to-end--
was visually detected by the spacecraft's optical navigation camera on the
very first attempt. To make this detection, the spacecraft's camera saw
stars as dim as 11th visual magnitude, more than 1,500 times dimmer than a
human can see on a clear night. Stardust's main camera, built for NASA's
Voyager program, will transmit the closest-ever comet pictures back to
Earth.

During the forthcoming January 2nd encounter, the comet particles will be
traveling five times faster than a rifle bullet, but the collecting aerogel
will stop this dust in a fraction of an inch. Because aerogel is as much as
99.9 percent empty space, the collision will not damage the grains or
appreciably alter their characteristics.

The spacecraft is scheduled to return to Earth two years later when a
capsule containing its treasure - less than an ounce of comet dust - will
parachute to the Utah desert. While thousands of tons of microscopic comet
particles blanket Earth each year, Brownlee said that, "unfortunately, they
are difficult to find among the earthly materials. And even when
extraterrestrial particles can be found, they are cosmic orphans - there is
no way to determine their origin."

In addition to understanding the origin of comets, the mission may offer
insights into how life originated on Earth. Comets are thought to have
delivered a significant share of the Earth's water, and "this [mission]
gives us a real opportunity to find out if our long-held suspicions are
right, that comets played a major role in the origin of life," Brownlee
said. "No one really knows how life began, but we're certain that carbon was
key to the process. Comets are the most carbon-rich materials in the solar
system, and we know they are full of organic compounds that fall on the
Earth all the time."

Astrobiology Magazine had the opportunity to talk with Professor Brownlee as
the Stardust spacecraft approached its dramatic encounter with a comet.

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Astrobiology Magazine (AM): When did your mission work on Stardust begin?

Don Brownlee (DB): We actually began this work in 1980 as a proposal to do
an "atomized sample return" from comet Halley. The mission (Halley Earth
Return, or HER) did not happen but it began a chain of developments and
proposals including sample return missions with ESA and Japan. The
breakthroughs were the development of intact capture using aerogel and the
NASA Discovery program.

Stardust was selected in 1995.

AM: What is the exact date predicted for the terrestrial return of samples
in the Utah desert?

DB: January 15, 2006.

AM: What are the logistical preparations for this mission, as the first
sample return since Apollo?

DB: A cleanroom for curation and distribution of the samples is being built
in Building 31 at the NASA Johnson Space Center in Houston. Special methods
are needed to handle and extract samples from the silica aerogel that they
are collected in, but after extraction the samples will be treated in ways
that are similar to those used for cosmic dust particles in the Cosmic Dust
lab also in Building 31.

Most samples will be 5 to 20 micron range-- identical to the typical cosmic
dust particles collected in the stratosphere. Stardust samples will usually
be studied by consortia groups around the world using sequences of different
techniques.

AM: What would be the typical organic compounds that one might expect to
find arround a comet?

DB: The most common nonvolatile organics are likely to be similar to those
found in carbonaceous chondites [carbon-rich meteorites]. This is likely to
be a kerogen-like material [waxy, organic solid] but we will see.

AM: When the aerogel sample from Stardust is taken to Houston's Johnson
Space Center, what sorts of tests are run? Mass spectroscopy and electron
micrographs?

DB: The initial inspection at JSC will be to measure track lengths and
estimate particle mass and state of preservation. Other work will be usually
done elsewhere by a wide range of techniques-- essentially all methods that
can be used to study nanogram and smaller samples.

AM: What is the tell-tale signature that the material is pristine and
cometary in origin? A particular ratio of key chemical elements from the
mass spectroscopy?

DB: If it collected by Stardust on the "comet side" of the aerogel it is
nearly 100% certain to be cometary. If we do pick up a few interplanetary
dust particles for even impact debris from the spacecraft, those particles
will not produce tracks perpendicular to the front plane of the collector.

This is the beauty of Stardust-- all particles on the comet side have a
known origin and are collected at exactly the same speed (6.1 km/s).

AM: What type of temperature control is possible within the aerogel to
preserve the state of the comet dust--for instance, what happens if a tiny
amount of water is captured in frozen form?

DB: Particles are pulse heated during capture-- a few microseconds. When
they are returned to Earth they are heated to ambient conditions -- perhaps
as much as 35 C. No liquid water will survive except as surface films on the
aerogel.

AM: There are many mission concepts for extending the Stardust collection
method, in particular for projectiles fired into Europa to stir up enough
particles that a flyby might collect surface samples without actually
landing. What is your opinion of these concepts?

DB: Both a Europa (Ice Clipper) and a Mars sample mission ("Sample
Collection for Investigation of Mars", or SCIM) have been proposed. They are
very interesting. Stardust-style sample collection has the great attraction
that it does not require landing.

AM: The actual encounter with the comet, Wild 2, will last a few minutes,
correct?

DB: Stardust will fly 300 km from the comet at 6 km/s. In two minutes it
will cover 90 degrees of phase angle. A few minutes is correct for most of
the collection and imaging.

AM: After the January 2nd encounter, how will you know that collection has
been nominal? Are there telemetry signals that give enough information to
infer capture?

DB: We will have a carrier signal during the encounter telling us that the
spacecraft is OK. The estimate of the success of the collection will be
based on the number of particles detected by the dust collector (Dust Flux
Monitor Instrument, or DFMI) and the mass spectrometer (Cometary and
Interstellar Dust Analyzer, or CIDA).

What's Next

Stardust, the fourth in NASA's Discovery missions and the first mission
designed to return samples from beyond Mars, was launched from Cape
Canaveral, Fla., on Feb. 7, 1999. It is currently on its third giant loop
around the sun, and will have traveled some 3.1 billion miles by the end of
its voyage. In November 2002 during an earlier asteroid flyby of Asteroid
5535 Annefrank, the spacecraft successfully tested systems it will use in
this week's Wild 2 encounter. During its nearly five years in space, it has
captured interstellar dust using the opposite side of the collector that
will gather the grains from Wild 2.

In the next 5 or so years, there will be no fewer than four to five
encounters of spacecraft with comets and asteroids. Of particular interest
next year, NASA's Deep Impact spacecraft is expected to make a stadium-sized
crater in Comet Tempel 1 on July 4 of 2005, making a large enough impact to
be visible through telescopes on Earth.

On Valentine's Day in 2001, the Near-Shoemaker spacecraft successfully
landed on the asteroid, 433 Eros. Its remarkable journey--to soft-land on a
peanut shaped asteroid about 176 million kilometers (109 million miles) from
Earth-- prompted Andrew Cheng, NEAR Project Scientist, to note: "On Monday,
12 February 2001, the NEAR spacecraft touched down on asteroid Eros, after
transmitting 69 close-up images of the surface during its final descent.
Watching that event was the most exciting experience of my life."

All the following missions are fully funded, though not all have been
launched:


2001 Sept. 22 Comet Borrelly Deep Space One (flyby)
2004 Jan. 2 Comet Wild 2 Stardust (coma sample return)
2005 July 4 Comet Tempel 1 Deep Impact (big mass impact)
2005 Sept. Asteroid 1998 SF36 Muses-C (sample return)
2014 Nov Comet Churyumov-Gerasimenko Rosetta (flyby/landing)

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Stardust is a collaboration of the UW, NASA and its Jet Propulsion
Laboratory at the California Institute of Technology, and Lockheed Martin
Space Systems. Other key members are The Boeing Co., the Max-Planck
Institute for Extraterrestrial Physics, NASA Ames Research Center and the
University of Chicago. Stardust, a part of NASA's Discovery Program of
low-cost, highly focused science missions, was built by Lockheed Martin
Astronautics and Operations, Denver, Colo., and is managed by JPL for NASA's
Office of Space Science, Washington, D.C. JPL is a division of the
California Institute of Technology in Pasadena. The principal investigator
is astronomy professor Donald E. Brownlee of the University of Washington in
Seattle.
Received on Wed 31 Dec 2003 03:53:03 PM PST