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."
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