[meteorite-list] Mars Rovers See Earth, Moon and Stars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:48 2004
Message-ID: <200403112154.NAA04716_at_zagami.jpl.nasa.gov>

http://www.space.com/scienceastronomy/mars_earth_040311.html

Mars Rovers See Earth, Moons and Stars
By Robert Roy Britt
space.com
11 March 2004

The Spirit rover on Mars took the first picture of Earth ever made from the
surface of another planet. It also did a little astronomy, imaging bright
stars.

It also spotted what could be a Viking Orbiter spacecraft or a meteor --
scientists aren't sure which.

The photo of Earth shows the planet as a bright dot above the horizon about
an hour before sunrise. The image is not in color, though scientists say if
a human stood in the same spot and looked earthward, home would probably
appear pale blue.

On the other side of the planet, Opportunity captured animated images of
Mars' moon Phobos eclipsing the sun. This, along with the previous image of
Deimos' solar eclipse, will help astronomers pin down the small moons'
orbits around the planet. Mark Lemmon, a rover science team member from
Texas A&M University, said Phobos' orbital position is uncertain, with its
actual route varying by about 6 miles (10 kilometers), which is roughly the
size of the moon itself.

Knowing Phobos' exact orbital path would allow satellites orbiting Mars to
obtain close-up photos of the moon. Researchers do not know if the moons
formed along with Mars or are captured asteroids.

Stars and streaks

Spirit is also seeing stars. The rover took nighttime images in the
direction of the constellation Orion. The bright star Betelgeuse is visible
in the upper right. Orion's belt, a row of three bright stars, can be seen
near the bottom of the photograph.

Faint specks on the image are the result of cosmic rays hitting the camera,
Lemmon said.

None of Spirit's astronomy images are part of the rover's primary mission,
but by taking more of them, scientists hope to learn something about the
amount of dust and water vapor in the nighttime atmosphere of Mars.

Another sky photo from Spirit shows a thin and short streak of light.

"That streak could have been a meteor," Lemmon said. Or it could have been
the Viking Orbiter 2, still circling Mars long after its 1970s mission
ended. Lemmon said the other nine spacecraft currently orbiting Mars --
three of which are presently in working order -- have known positions and
did not create the streak.

Spirit reaches Bonneville

Meanwhile, carrying out its day job, Spirit has finally peered down into an
impact crater called Bonneville. It is the first view of a good-sized impact
crater on Mars ever taken from this vantagepoint, said Matt Golombek of
NASA's Jet Propulsion Laboratory (JPL).

The crater does not appear to harbor any sedimentary rock outcroppings, like
what was found at the Opportunity landing site, Golombek said at a press
conference today. Instead, the rocks around the rim appear to all be similar
to rocks the rover has encountered running up to the rim. They are all
thought to have been cast out by an ancient impact.

The lack of outcroppings of bedrock is somewhat of a disappointment for
scientists, because it suggest there might not be any easy-to-find signs of
standing water at the Spirit site. The craft has found signs of past water
associated with volcanic activity, but not the sort of soggy situation
revealed by Opportunity.

Spirit will explore the crater rim for a week or two before deciding whether
to drive down in or move on toward the distant East Hills. The decision will
be made based on both science and rover safety.

On the other side of the planet, the Opportunity rover is in the process of
analyzing the "blueberry bowl," a high concentration of BB-sized spheres.
Scientists are confident the spheres, which they sometimes call blueberries,
formed in water, but they don't yet know their composition.

Hematite was water-generated

One of Opportunity's next tasks will be to further investigate a mineral
called hematite, which is abundant on the plains that surround the shallow
depression in which the robot landed. Phil Christensen of Arizona State
University in Tempe said the latest infrared observations show the hematite
is highly concentrated in hot spots.

"We call them the mother lode of hematite," Christensen said. The hotspots
suggest the hematite has been on the plains for perhaps a billion years and
has been broken up from an original rock. He also figures the hematite was
long ago punched out of the landing-site crater, which contains very low
quantities of the mineral.

Over the eons, some hematite has been transported back down into the shallow
crater, but "that's a very slow process," he said.

On Earth, hematite usually forms in the presence of standing water.
Scientists had sought to determine if water was the source of the Martian
hematite, which had first been detected from orbiting spacecraft and was one
reason Opportunity's landing site was picked.

Given the discovery of past water at Opportunity site announced earlier this
month, "I think it's fair to say the hematite also formed in water,"
Christensen said. His team will now try to find out how the hematite fits
into the overall story of past water on Mars.
Received on Thu 11 Mar 2004 04:54:17 PM PST