The Thermal Emission Imaging System (THEMIS) is a camera that images Mars in the visible and infrared parts of the spectrum in order to determine the distribution of minerals on the surface of Mars. It is used to determine the distribution of minerals on the surface of Mars and help understand how the mineralogy of the planet relates to the landforms.

THEMIS was also named after the ancient Greek goddess of justice.

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 will search for active thermal spots and may discover "hot springs" on Mars.

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 significantly improves the data from the Thermal Emission Spectrometer (TES), a similar instrument on Mars Global Surveyor.

The instrument's multi-spectral approach will also provide data on localized deposits associated with hydrothermal and subsurface water and enable 100-meter (328-feet) images of Martian terrain to be captured in each pixel, or single point, of every image.

Advanced Spaceborne Thermal Emission and Reflection Radiometer (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.

How THEMIS works in the visible

Using visible imaging in five spectral bands, the experiment will also take 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)--will be acquired for Martian surface studies. These more detailed data will be used in conjunction with mineral maps to identify potential landing sites for future Mars missions.

The part of the imaging system that takes pictures in visible light will be able to show objects about as big as a semi-truck. This resolution will help 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 specifications

The Thermal Emission Imaging System weighs 11.2 kilograms (24.7 pounds). It is 54.5 centimeters (21.5 inches) by 37 centimeters (14.6 inches) by 28.6 centimeters (11.3 inches). THEMIS runs on 14 watts of electrical power.

External links

• http://mars.jpl.nasa.gov/odyssey/mission/instruments.html - THEMIS Specs
• http://mars.jpl.nasa.gov/odyssey/technology/themis.html - THEMIS
• http://mars.jpl.nasa.gov/odyssey/mission/profileChristensen.html - A word from THEMIS' lead scientist
• http://themis.asu.edu - THEMIS intrument site at Arizona State University