Figure: Hematite

This mosaic of infrared images shows the abundance and location of hematite at Opportunity's landing site, Meridiani Planum. On Earth, hematite is a mineral that typically forms in water.

The thermal emission imaging system (THEMIS) on Odyssey is both an infrared camera and a visible camera. It has captured telltale signs of past water on Mars. In four locations on Mars, THEMIS has detected high levels of hematite, a mineral that on Earth forms most often in the presence of liquid water. Discoveries by THEMIS and its predecessor instrument (TES, thermal emission spectrometer) on the Mars Global Surveyor orbiter led the 2003 Mars Exploration Rover mission team to choose Meridiani Planum as a landing site for its hematite content.

Since landing, data from the Opportunity rover's science instruments, including the miniature thermal emission spectrometer (mini-TES) has since confirmed THEMIS' results that the area was once covered in water.

"The morphology and thermal properties of the Meridiani Planum region indicate that the hematite-bearing area was deposited in a standing body of water that extended over 100,000 square kilometers, with smaller bodies of water in nearby crater basins," said Christensen.

THEMIS, along with Christensen's two other instruments at Mars (TES on Mars Global Surveyor and mini-TES on the rovers), has shown that liquid water could have been in a few areas within the equatorial region of Mars for thousands or tens of thousands of years.

Credit: NASA/JPL/Arizona State University

http://mars.jpl.nasa.gov/spotlight/images/End_Themis_040820205617.jpg

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http://mars.jpl.nasa.gov/spotlight/odyssey-mission-success.html