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THEMIS: The Thermal Emission Imaging System |
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By looking at the visible and infrared parts of the spectrum, THEMIS is determining the distribution of minerals on the surface of
Mars and helping scientists understand how the mineralogy of the planet relates
to the landforms.
A word from THEMIS' lead scientist
How THEMIS Works in the Infrared
During the martian day, the sun heats the surface. Surface minerals
radiate this heat back to space in characteristic ways that can be
identified and mapped by the instrument. At night, since it maps heat,
the imager searches for active thermal spots.
In the infrared spectrum, the instrument uses 9 spectral bands to
help detect minerals within the martian terrain. These spectral bands,
similar to ranges of colors, can obtain the signatures (spectral "fingerprints")
of particular types of geological materials. Minerals, such as carbonates,
silicates, hydroxides, sulfates, hydrothermal silica, oxides and
phosphates, all show up as different colors in the infrared
spectrum. This multi-spectral method allows researchers to detect
in particular the presence of minerals that form in water and to
understand those minerals in their proper geological context. THEMIS'
infrared capabilities have significantly improved the data from TES, a
similar instrument on Mars Global Surveyor.
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The instrument's multi-spectral approach also provides data on
localized deposits associated with hydrothermal and subsurface water
and enables 100-meter (328-feet) images of martian terrain to be
captured in each pixel, or single point, of every image.
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ASTER, an Earth orbiting instrument on the Terra
spacecraft, has used a similar approach to map the distribution of minerals
here on Earth.
Variations in the thermal infrared "color" in the right-hand image are due
to differences in the kinds of minerals that make up rocks and soil. In the
visible part of the spectrum that our eyes can see (left-hand image), it would
not be apparent what minerals are present.
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How THEMIS Works in the Visible
Using visible imaging in five spectral bands, the experiment
also takes 18-meter-resolution (59-foot) images to determine the
geological record of past liquid environments on Mars. More than 15,000 images-- each 20X20 kilometers
(12X12 miles)-- have been acquired for martian surface studies. These
more detailed data were used in conjunction with mineral maps to
identify potential landing sites for the 2003 Mars Exploration Rover
mission and new images will be used for future Mars missions.
The part of the imaging system that takes pictures in visible
light is able to show objects about as big as a semi-truck.
This resolution helps fill in the gap between large-scale geological
images from the Viking orbiters in the 1970s and the very
high-resolution images from the currently orbiting Mars Global Surveyor.
THEMIS Specs
For more information, visit the THEMIS instrument site at Arizona State University
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