[meteorite-list] 'Shooting Stars' On Mars: Messages From A Meteorite

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Jan 26 13:40:56 2005
Message-ID: <200501261840.KAA12629_at_zagami.jpl.nasa.gov>

http://space.com/missionlaunches/mars_meteorites_050126.html

'Shooting Stars' On Mars: Messages From A Meteorite
By Leonard David
space.com
26 January 2005

NASA's Opportunity Mars rover has completed its inspection of "Heat
Shield Rock" -- an iron meteorite the robot came across at Meridiani
Planum, a cratered flatland that the machine has called home since
landing on the red planet over a year ago.

The pitted, basketball-size meteorite is mostly made of iron and nickel,
as detected by the rover's set of onboard spectrometers -- devices that
map the presence of different elements on the surface of Mars.

Meteors, often called "shooting stars" have been seen blazing through
the Martian sky by both Opportunity and its sister ship, Spirit, now
rolling through the Columbia Hills at Gusev Crater.

But finding the meteorite was a surprise to scientists running the dual
Mars Exploration Rover effort. The researchers now wonder just how
prolific meteorites might be, perhaps sitting there strewn across the
expanse of Meridiani Planum.

Sitting there a very long time

"We're done with the meteorite," said Steve Squyres from Cornell
University, and the leader of the science team for the Mars Exploration
Rover (MER) mission.

Squyres told SPACE.com that further study of nearby entry shield
hardware that slammed onto Mars during Opportunity's landing is on tap,
followed by setting sail to the south toward a circular feature called
"Vostok".

Discovering the meteorite has raised some speculation it might have been
dislodged from a different locale -- "unmarsed" so to speak -- and
tossed to its present position by the high-speed impact of Opportunity's
entry shield, but Squyres said there was "no morphologic evidence for
disturbance of soil around the meteorite."

"It has been sitting there a very long time," Squyres said.

Difficult questions to answer

There are a number of things that make the meteorite find a very
scientifically interesting and important find, said planetary geologist,
Bradley Jolliff of Washington University in St. Louis, Missouri and a
MER science team member.

"From the well-preserved shape and form of cuspate marks and
'thumb-print'-like cavities, it is possible to say something about the
velocity and atmospheric effects that this meteorite experienced when it
fell," Jolliff said.

How fast the meteorite struck Mars, and just how thick was the martian
atmosphere during its fall are difficult questions to answer. "But
careful study will likely provide some constraints. The external shapes
and overall morphology suggest that this was not a piece broken off from
a larger object, but that this is the entire meteorite," Jolliff told
SPACE.com.

Recent event or ancient?

Rover scientists are also studying the microscopic images of the
meteorite taken by Opportunity. They're on the lookout for any features
that might record the level of shock experienced when the object hit the
surface to help bracket possible velocity ranges, Jolliff said.

"We can look for any tell-tale signs of an impact to determine if
perhaps this was a recent event or an ancient one," Jolliff
explained. "It may be that this meteorite has been buried and re-exhumed
by inflation and deflation of the Meridiani surface regolith over time."

Important questions: If the meteorite is very old, is the external
surface weathered or oxidized? Also, what has been the interplay between
the meteorite and possible weathering and abrasion by wind-blown sand
particles?

Ground-truth learning tool

Scientists are taking a hard look at the nooks and crannies of the
object using Opportunity imagery and other data. By inspecting different
parts of the meteorite's surface and its "protected" hollows, the tale
of what reactions have occurred between the metal and the thin martian
atmosphere may be gleaned.

"In this case, study of the meteorite is providing clues about the
surface and atmosphere of Mars," Jolliff added. Close-up exam of the
object by the rover's camera and Mini-Thermal Emission Spectrometer
(Mini-TES) has meant giving them a sort of a ground-truth learning tool,
he said.

"Now we can recognize these objects, which might be common on the
Meridiani surface, without having to drive up close to them. Their
spectral signature and contrast are quite unique," Jolliff explained.

Fascinating place to explore

Opportunity's discovery of the meteorite is a very important scientific
find for another reason.

"Consider the Apollo samples from the Moon. With the exception of a few
very tiny bits of meteorite and meteoritic metal, there have been no
'large' meteorites found," Jolliff recalled. "Of course, there is no
atmosphere to slow them down. Yet we suspect that they must be
plentiful, even if small, and one day, when we can sample and analyze
[lunar] surface materials routinely, we will likely find lots of them."

They may represent a different "sampling" of meteorite populations in
space and time, Jolliff continued, "and thus give us new insights to the
origins of specific types of meteorites."

One question in Jolliff's mind is whether the distribution of meteorite
types found today on Earth is representative of the meteorite
distribution of past epochs as well, and of different locations in the
solar system.

"This find on Mars reinforces that Mars' surface also holds great
potential in this regard, especially a flat surface such as Meridiani
Planum. It has been likened to some of the ablating ice surfaces in
Antarctica where many -- and in some places nearly all -- of the rocks
at the surface are meteorites," Jolliff pointed out. "What a
spectacularly fascinating place to explore!"

Unknown cycles and intensities

There's yet another incentive to get a handle on the "rainfall" of
meteors plowing into and through the thin martian atmosphere.

Just how vulnerable are spacecraft orbiting Mars, as well as crews
staying for extended stays on the planet?

"There is pure scientific interest in knowing the frequency, intensity,
and radiants of martian meteor showers. Being in a different orbit than
Earth and closer to the asteroid belt, Mars has unknown cycles and
intensities of meteoroid hazards. Knowledge of these hazards can help us
manage risk in future missions, particularly extended and crewed
missions."

That's the view of the Oregon L5 Society in a research paper advocating
a Mars meteor survey, presented back in July 2000 to a Concepts and
Approaches for Mars Exploration workshop, sponsored by the Lunar and
Planetary Institute in Houston, Texas.

Great meteoritical museum

The research group has advocated outfitting instruments on one or more
Mars landers to identify and characterize the meteoroid flux at Mars.

Along with a camera, the survey gear would include a radio (or
microwave) device to pick up a radio frequency signal created by
meteoroid entry; a microphone to perhaps detect any sonic boom or other
sound generated by a meteoroid entry; as well as a seismometer to record
a seismic signal stemming from a meteor impact.

Such equipment could help assess the nature of martian meteor showers,
how big are they and where do they come from. Also, the gear might
determine whether or not meteor storms can be predicted on Mars.
Moreover, could surface operations of human expeditions be exposed to
periodic "rains of rock"?

According to Bob McGown of Portland, Oregon, leader of the research team
on the Mars meteor survey idea, the red planet may well be a storehouse
of fallen shooting stars.

"There is the idea that the red dusty surface of Mars is from the
rusting of iron-nickel meteorites on the surface", McGown told SPACE.com.
"Also, a rock from Venus or from Mercury has never been found. The
deserts of Mars could be like a great meteoritical museum or space
laboratory - a collecting ground of rocks from other worlds."
Received on Wed 26 Jan 2005 01:40:44 PM PST