[meteorite-list] Opportunity Discovers Tiny Craters on Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed May 18 17:31:58 2005
Message-ID: <200505182131.j4ILVL224482_at_zagami.jpl.nasa.gov>

http://marsrovers.jpl.nasa.gov/spotlight/opportunity/20050427.html

Opportunity Discovers Tiny Craters on Mars
Jet Propulsion Laboratory
April 27, 2005

On Earth, people tend to think of craters as giant holes in the ground
like Meteor Crater in Arizona, ancient features too big to miss that
mark the site of a catastrophic collision with an asteroid or comet.

But craters can also be small objects, like the two discovered recently
by the Opportunity rover on the plains of Meridiani on Mars. Both are
less than half an inch deep and clearly visible in images taken by the
rover's navigation cameras.

"These are the smallest craters yet observed by either rover," said Matt
Golombek, a veteran Mars researcher at NASA's Jet Propulsion Laboratory
and principal scientist on the Mars Exploration Rover mission. "I think
the smallest crater we saw in Gusev Crater (where Opportunity's twin,
the Spirit rover, is exploring the other side of Mars) was 40
centimeters (15.7 inches) wide and that was in a hollow that had already
been filled by sand and sediment."

The largest of the two craters discovered by Opportunity is only half as
big, measuring 20 centimeters (7.9 inches) in diameter and 1 centimeter
(0.4 inches) deep. The smallest of the two is 10 centimeters (3.9
inches) wide and less than 1 centimeter deep. Opportunity took pictures
of the two tiny craters with its left and right navigation cameras,
creating a stereo image that allowed scientists to measure their
distance and size.

On Earth, small craters are not commonly recognized because they're
quickly filled with dirt, pine needles, or other debris carried by water
and wind. On Mars, craters are primarily filled by wind-blown sediment,
though in the past they may also have been filled by lava, melting ice,
or flowing water.

"Given that these two craters haven't been covered by sand even though
they are surrounded by sand ripples on a flat plain lends support to the
idea that they're fairly recent," said Golombek. "Of course, recent
might mean any time from yesterday to 100 million years ago."

Both are impact craters formed either by an object from space that was
large enough to make it through the martian atmosphere without burning
up or by rock fragments ejected from a larger crater that formed when
something crashed into the martian surface.

"Come to think of it," added Golombek, "there were also no small, fresh
craters seen by the previous three martian landers, which include
Pathfinder and the two Viking landers. These are the smallest craters
yet seen on Mars." Golombek was project scientist for the Pathfinder
mission.
Received on Wed 18 May 2005 05:31:20 PM PDT