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Дата: 01 июля 1998 (1998-07-01)
От: Alexander Bondugin
Тема: Water History, Rock Composition Among Latest Findings A Year After Mar
Subject: Water History, Rock Composition Among Latest Findings A Year After Mar
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CALIFORNIA INSTITUTE OF TECHNOLOGY
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PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Contact: Diane Ainsworth
FOR IMMEDIATE RELEASE June 29, 1998
WATER HISTORY, ROCK COMPOSITION AMONG LATEST FINDINGS A YEAR AFTER MARS
PATHFINDER
A year after the landing of Mars Pathfinder, mission scientists say
that data from the spacecraft paint two strikingly different pictures of the
role of water on the red planet, and yield surprising conclusions about the
composition of rocks at the landing site.
"Many of the things that we said last summer during the excitement
after the landing have held up well," said Dr. Matthew Golombek, Pathfinder
project scientist at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA.
"But we have now had more time to study the data and are coming up with some
new conclusions."
Similar to on-going science results from NASA's Mars Global Surveyor
spacecraft currently in orbit around Mars, Pathfinder data suggest that the
planet may have been awash in water three billion to 4.5 billion years ago.
The immediate vicinity of the Pathfinder landing site, however, appears to
have been dry and unchanged for the past two billion years.
Several clues from Pathfinder data point to a wet and warm early
history on Mars, according to Golombek. Magnetized dust particles and the
possible presence of rocks that are conglomerates of smaller rocks, pebbles
and soil suggest copious water in the distant past. In addition, the bulk of
the landing site appears to have been deposited by large volumes of water,
and the hills on the horizon known as Twin Peaks appear to be streamlined
islands shaped by water.
But Pathfinder images also suggest that the landing site is
essentially unchanged since catastrophic flooding sent rocks tumbling across
the plain two billion years ago. "Since then this locale has been dry and
static," he said.
While the area appears to have been untouched by water for eons, wind
appears to have been steadily eroding rocks at the landing site. Analysis of
Pathfinder images shows that about about three to five centimeters (one to
two inches) of material has been stripped away from the surface by wind,
Golombek noted.
"Overall, this site has experienced a net erosion in recent times,"
said Golombek. "There are other places on Mars that are net 'sinks,' or
places where dust ends up being deposited. Amazonis Planitia, for example,
probably has about one to two meters (three to six feet) of fine, powdery
dust that you would sink into if you stepped on it."
Chemical analysis of a number of rocks by the alpha proton X-ray
spectrometer (APXS) instrument on Pathfinder's mobile Sojourner rover,
meanwhile, reveals an unexpected composition that scientists are still
trying to explain.
The current assessment of data from this instrument suggests that all
of the rocks studied by the rover resemble a type of volcanic rock with a
high silicon content known on Earth as andesite, covered with a fine layer
of dust. All of the rocks appear to be chemically far different from
meteorites discovered on Earth that are believed to have come from Mars.
"The APXS tells us that all of these rocks are the same thing with
different amounts of dust on them," said Golombek. "But images suggest that
there are different types of rocks. We don't yet know how to reconcile
this."
When molten magma oozes up from a planet's mantle onto the surface of
the outer crust, it usually freezes into igneous rock of a type that
geologists call a basalt. This is typical on the floors of Earth's oceans,
as well as on the maria of the Moon and in many regions of <b style="color:black;background-color:#ffff66">Mercury</b> and
Venus. By contrast, andesites typically form on Earth in tectonically active
regions when magma rises into pockets within the crust, where some of its
iron and magnesium-rich components are removed, leaving rock with a higher
silicon content. "We don't believe that Mars has had plate tectonics, so
these andesites must have formed by a different mechanism," Golombek said.
The rocks studied by Pathfinder most closely resemble andesites found
in Iceland and the Galapagos Islands, tectonic spreading centers where
plates are being pushed apart, said Dr. Joy Crisp, an investigation
scientist on the spectrometer experiment at JPL. Andesites from these areas
have a different chemical signature from andesites formed at subduction
zones, mostly because wet ocean sediments carry more water down into the
mantle at the subduction zones. "On Mars, where the water content is
probably lower and there is no evidence of subduction, we would expect a
closer chemical similarity to Iceland andesites," said Crisp.
The Martian rocks may have other origins, however. They could be
sedimentary and influenced by water processes; they could be formed by
melting processes resulting from a meteor impact; or, a third alternative is
that the rocks might be basaltic, but covered by a silicon-rich weathering
coating. "In any event, the presence of andesites on Mars is a surprise, if
it is borne out as we study the data further," said Crisp. "Most rocks on
Mars are expected to be basalts lower in silicon. If these are in fact
andesites, they are probably not very abundant."
Pathfinder scientists are looking forward to more data from the
Thermal Emission Spectrometer instrument on the Mars Global Surveyor to
reveal more about the chemical composition of the planet's surface,
especially once the orbiting spacecraft begins its prime circular mapping
mission in spring 1999.
In other recent Pathfinder science findings, Dr. Steven Metzger of
the University of Nevada found direct evidence of gusting winds called "dust
devils" in images from Pathfinder's lander. Such dust devils had been seen
in some Viking orbiter images and inferred from measurements of atmospheric
pressure and winds by other instruments on the Pathfinder lander, but were
not spotted in actual surface images until Metzger's discovery.
JPL planetary scientist Dr. Diana Blaney has been using data from
Pathfinder, other spacecraft missions and ground-based observations to study
weathering on Mars. Her work suggests that Mars is uniformly covered by a
fine coating of dust formed by an unusual process involving meteor impacts
and volcanic gases that add sulfur.
NASA's next Mars missions, the 1998 Mars Climate Orbiter and Mars
Polar Lander, are in testing now for launch in December and January,
respectively. Whereas Pathfinder's science focus was on exploring rocks with
its mobile robotic geologist, the Mars Polar Lander will focus on a search
for water under the planet's surface, equipped with a robot arm that will
dig into the soil at the landing site near the planet's south pole.
Launched on December 4, 1996, Pathfinder reached Mars on July 4,
1997, directly entering the planet's atmosphere and bouncing on inflated
airbags as a technology demonstration of a new way to deliver a lander and
rover to Mars. The lander operated nearly three times its design lifetime of
30 days, while the rover operated 12 times its design lifetime of seven
days.
During the mission, the spacecraft relayed an unprecedented 2.3
gigabits of data, including 16,500 images from the lander's camera, 550
images from the rover camera, 16 chemical analyses of rocks and soil, and
8.5 million measurements of atmospheric pressure, temperature and wind.
Mars Pathfinder was designed, built and operated by JPL for NASA's
Office of Space Science, Washington, DC. JPL is a division of the California
Institute of Technology, Pasadena, CA.
#####
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Дата: 01 июля 1998 (1998-07-01)
От: Alexander Bondugin
Тема: February Launch Planned For Mission To Collect Samples Of Comet Dust
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FOR IMMEDIATE RELEASE
FROM: Vince Stricherz
University of Washington
206-543-2580
vinces@u.washington.edu
DATE: June 29, 1998
February launch planned for UW mission to collect samples of comet dust
It might sound like something from a
popular science fiction movie, but a
University of Washington astronomy
professor's nearly two-decade dream of
launching an unmanned spacecraft to collect
interstellar dust from a comet is close to
coming true.
Stardust will blast off from Cape
Canaveral, Fla., in February. It will be
the fourth mission in NASA's Discovery
series, which captured public imagination a
year ago with Mars Pathfinder. It will be
the first mission since Apollo to return
samples of space material to Earth for
analysis.
UW professor Donald Brownlee, the principal investigator for the project,
expects to find clues about the formation of the solar system and perhaps
the universe itself.
"We hope to understand how comets were formed and what they're made of," he
said. "We expect them to be the preserved building blocks of the outer
planets."
Brownlee began considering such a mission in1980. The idea was explored
seriously five years later when Halley's comet approached Earth, but it was
deemed unworkable then.
For Stardust's 7-year, 3.1-billion-mile journey, solar panels will power the
spacecraft to encounter Wild 2, a comet that altered course in 1974 after a
close encounter with Jupiter. Now instead of circling among the outer
planets in our solar system, Wild 2 (pronounced vihlt 2) travels among the
inner planets. It was discovered in 1978 during its first close approach to
Earth.
Wild 2's recent arrival to the planetary neighborhood makes the $200 million
Stardust mission possible. In 2004, the craft will pass about 75 miles from
the main body of the comet. That's close enough to trap small particles from
the comet's coma, the gas-and-dust envelope surrounding the nucleus. A
camera built for NASA's Voyager <b style="color:black;background-color:#66ffff">program</b> will transmit the first-ever
close-up comet pictures back to Earth. Though the encounter will last about
12 hours, Brownlee says the really intense activity will be over in a matter
of minutes.
The collection system will extend from the spacecraft and trap particles as
they collide with it. To prevent damaging or altering the particles - each
smaller than a grain of sand and traveling as much as nine times the speed
of a bullet fired from a rifle - the collector uses a unique substance
called aerogel. Often called "frozen smoke," aerogel is a transparent blue
silica-based solid that is as much as 99.9 percent air. It is as smooth as
glass, something like plastic foam without the lumps. A block the size of a
person weighs less than a pound but can support the weight of a small car.
On the trip to Wild 2, the aerogel-equipped collection panel will be
deployed to trap interstellar particles traveling in space. During the
encounter with the comet, some 242 million miles from Earth, the opposite
side of the panel will gather bits of comet dust. Trapped particles will
leave a telltale trail through the aerogel that scientists will follow to
find the grains and extract them. Upon leaving the comet, the collection
panel will retract into its capsule.
Once the Stardust capsule parchutes into Utah's Great Salt Desert in 2006,
the particles it collects will go to Johnson Space Center in Houston and
then be parceled out to various research facilities, including the
University of Washington. Because comets are about equal parts ice and dust,
Brownlee believes the particles will be cryogenically preserved interstellar
dust left from the birth of the solar system some 4.6 billion years ago.
Such grains can be found only in the outer solar system, he believes,
because heat has destroyed them nearer the Sun.
Brownlee's previous work collecting cosmic dust particles led to their being
named Brownlee particles. Cosmic dust was brought back to Earth on Gemini
missions in the 1960s. Later, high-flying U2 planes and balloons gathered
particles from different levels in the atmosphere, and space dust even has
been collected from the ocean floor. "A comet mission is the logical
extension," Brownlee said.
The project is being carried out by a consortium that includes the Jet
Propulsion Laboratory and Lockheed Martin Astronautics. When it came to
picking a name, Brownlee said, it just seemed appropriate to select
"Stardust," the title Hoagy Carmichael put on a popular tune that since has
been recorded by numerous artists, including Willie Nelson and Ringo Starr.
"I liked it because most spacecraft missions had weird, bizarre names. They
were acronyms for something," he said. "This isn't an acronym for anything.
It's just a name that people know."
###
For more information, contact Brownlee at
brownlee@bluemoon.astro.washington.edu or (206) 543-8575.
FOR IMMEDIATE RELEASE
FROM: Vince Stricherz
University of Washington
206-543-2580
vinces@u.washington.edu
DATE: June 17, 1998
"Send Your Name to a Comet" effort proves very popular
Hundreds of thousands of people will get a vicarious thrill tracking the
progress of the Stardust mission to comet Wild 2 in the next seven years,
knowing their names are inscribed on a microchip that is going along for the
ride.
In fact, NASA collected 130,000 names for one microchip already loaded on
the Stardust spacecraft, and more than 200,000 names have been placed on a
second. The names are etched electronically on a chip the size of a
fingernail, with writing so small that 80 letters will fit into the width of
a human hair and an electron microscope is needed to read them.
University of Washington Astronomy Professor Donald Brownlee, the father of
the Stardust mission, said plans are to place the chips in a museum when the
spacecraft returns to Earth in early 2006. He hopes they will go to the
Smithsonian Institution.
The drive to gather names for the mission has gotten new emphasis with the
recent release of the movie Deep Impact, a science-fiction thriller about a
comet colliding with Earth, and the imminent release of "Armageddon," about
an asteroid colliding with Earth. Paramount Studios and and the DreamWorks
SKG, which collaborated on "Deep Impact," are promoting the gathering of
names.
The only way to submit a name for inclusion on a chip is through Stardust's
web page, http://stardust.jpl.nasa.gov. Submitting a name automatically
grants permission for the name to be used in future exhibits and
publications by the Stardust collaboration, which includes the UW, NASA, the
Jet Propulsion Laboratory and Lockheed Martin Astronautics.
###
STARDUST MISSION TIMELINE
1929: Hoagy Carmichael writes the song "Stardust."
1974: Close encounter with Jupiter causes major orbital shift for comet Wild 2
1978: Wild 2 discovered by Swiss astrophysicist Paul Wild on Jan. 6 during
its first close approach to Earth.
1995: NASA selects Stardust mission to retrieve samples from Wild 2.
1999: Launch of Stardust spacecraft scheduled for Feb. 6.
2000: March through May, interstellar dust collection.
2001: Jan. 15, Stardust passes near Earth to get a gravitational speed boost.
2002: July through December, interstellar dust collection.
2004: Jan. 2, encounter with Wild 2; spacecraft will fly through comet's
coma, take pictures and collect dust samples.
2006: Jan. 15, spacecraft returns to earth; capsule containing comet samples
dropped by parachute to the Utah Test Training Range; speed of 13
kilometers
(about 7 miles) per second is the fastest for any re-entry vehicle.
SOME STARDUST MISSION FACTS AND FIGURES
Principal investigator: Don Brownlee, University of Washington astronomy
professor
Miles traveled: About 3.1 billion.
Distance from Earth during comet encounter: About 242 million.
Spacecraft: Weight 375 kilograms (about 825 pounds), about the size of an
average office desk.
Capsule: About 30 inches across and 20 inches deep.
Thrusters: About 1 inch long and 0.5 inch wide, they look something like a
pawn in a chess game (Manufactured by Primex Aerospace Co. of Redmond,
Washington).
Camera: A spare from NASA's Voyager <b style="color:black;background-color:#66ffff">program</b>, it has been retooled for this
mission but contains the original optics; a new camera would cost a
prohibitive $25 million to $30 million.
Transmitter: A dish-shaped antenna about 3.3 feet across will send images of
Wild 2 back to Earth (Manufactured by The Boeing Co., Tukwila, Wash.).
Solar panels: They will collect energy from the sun to provide electrical
power to the spacecraft.
Assembly: Conducted at the Lockheed Martin Astronautics in Denver;
continually updated pictures of the work can be seen at the Stardust home
page.
Launch vehicle: A Delta II rocket made by Lockheed Martin.
Collaborators: The project is being done for NASA by the University of
Washington; the Jet Propulsion Laboratory in Pasadena, Calif., a division of
the California Institute of Technology; and Lockheed Martin.
SOME FACTS ABOUT AEROGEL
Discovered: In the late 1930s, though scientists continue puzzling over its
properties
Manufacturing process: Supercritical drying is used to extract the liquid
from silica dioxide gel (similar in form to a gelatin dessert); normal.
evaporation would cause the gel to collapse, but in this process the gel
keeps its form.
Density: The lowest of any known solid; one form is 99.9 percent air and 0.1
percent silica dioxide.
Strength: A block the size of a human being would weigh less than a pound
but could support a car weighing 1,000 pounds.
Other uses: It is being considered as a non-flammable alternative to
insulation and sound-proofing in walls and windows; it could be used as
lightweight insulation in aircraft.
###
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