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Thermal imager probes Mars’ surface

09 Jun 2003

Detailed images of the surface of Mars appear in this week’s issue of Science.

Images and analysis of a year’s worth of data sent back from the Thermal Emission Imaging System (THEMIS) onboard NASA’s Mars Odyssey spacecraft are unveiled in this week’s Science. By revealing the make-up and thickness of rock layers, the infrared images are helping geologists understand how the environmental conditions on Mars have changed.

THEMIS boasts a thermal infrared multispectral imager operating between 6.5 and 15 microns and a camera operating in the visible to near-infrared (450 to 850 nm).

“THEMIS is creating a set of data that is going to revolutionize our mapping of the planet and its geology,” said Philip Christensen, THEMIS principle investigator from Arizona State University. “It will keep Mars scientists busy for the next 20 years trying to understand the processes that have produced this landscape.”

The 100m spatial resolution of the THEMIS thermal images is said to be 300-times better than that of the thermal emission spectrometer on NASA’s Mars Global Surveyor (MGS). “The camera on MGS takes exquisite images that show layers, but it doesn’t tell me anything about the composition,” says Christensen. “With the THEMIS temperature data, I can actually get an idea – each layer has remarkably different physical properties.”

Daytime and nighttime temperature data allow the THEMIS scientists to distinguish between solid rock and loose materials. Small particles heat up and cool down more rapidly than solid rock that retains heat.

Among many results, the THEMIS team has discovered that the planet has experienced dramatic environmental change. “It’s very difficult to say exactly what happened in any particular place, but what we’ve found is that in many places it hasn’t just been the same thing happening for year-after-after year for billions of years.”

Christensen’s team has also seen km-scale regions of exposed bedrock, where sand has stripped away and eroded the overlying layers. Hyperspectral data from THEMIS has also been used to identify minerals present on the martian surface. Of particular interest is a 50 – 100 m thick layer of a water-soluable mineral called olivine near the bottom of the Ganges Chasma canyon. “If there was groundwater present, the olivine would have disappeared,” said Christensen. “We know that some places on Mars have water, but here we see that some really don’t.”

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