Space Topics: Mars Exploration Rovers
The Year in Pictures: 2009
Massive Meteorite Makes Martian Mile Marker
Credit: NASA / JPL / Cornell / color mosaic by James Canvin |
The Mars Exploration Rover
Opportunity has spent 2009 on a road trip,
steadily driving southward on a nearly 20-kilometer (12-mile) journey
toward Endeavour crater. The dune-filled landscape of Meridiani Planum
is numbingly similar day after day, with rare but interesting small craters
and cobbles providing fodder for images as Opportunity drives by. Two
days after it roved by this rock, Opportunity’s scientists realized they’d
passed something special, so they turned around and returned to it,
spending nearly two months examining it with all instruments.
Opportunity’s studies
confirmed that the rock, now named “Block
Island,” is an enormous iron-nickel meteorite. At more than half a meter
in length and likely more than half a ton in mass, it is larger than any
other known meteorite on Mars, large enough to be visible from the
HiRISE camera on Mars Reconnaissance Orbiter. In fact, it is so big that
its existence on the Martian surface is problematic: at Mars’ current
atmospheric pressure, Block Island should have come in with so much
velocity that it should have shattered. The fact that it is intact suggests
to scientists that when it landed, the atmosphere was thicker than it
is now.
Block Island up close
Opportunity used its microscopic imager to get this view of the surface of Block Island on its Sol 1963(Aug. 1, 2009). The triangular pattern of small ridges seen at the upper right in this image and elsewhere on the rock is characteristic of iron-nickel meteorites found on Earth, especially after they have been cut, polished and etched. Block Island has been identified as an iron-nickel meteorite based on this surface texture and analysis of its composition with the alpha particle X-ray spectrometer. At about 60 centimeters (2 feet) across, it is the largest meteorite yet found on Mars. This image shows a patch 32 millimeters by 32 millimeters (1.3 inches by 1.3 inches)
Credit: NASA / JPL-Caltech / Cornell University / USGS
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