With most geologic samples, the composition of the minerals in the rock is important information for understanding how the rock formed and what has happened to it in the time since its formation. Many techniques, such as electron microprobe, determine composition on a mineral by mineral basis, requiring several small samples that often have to be specially prepared for the analysis technique. Middle infrared spectroscopy is just another way of analyzing the composition of a sample, with a few distinct advantages:

• You can analyze the entire rock sample at once, without preparing it in any way (no cutting, polishing, crushing or powdering)
• Because the natural emitted energy of the sample is what is measured, this technique is passive and the sample is not damaged or destroyed by a beam of energy
• Thermal emission spectra allow you to obtain compositional information about all of the minerals in the rock in one analysis
• You can deconvolve the rock spectrum to determine not only the compositions but also the abundances of each mineral in the rock

Thus, the nondestructive nature of this technique is highly desireable for analyzing delicate or valuable samples, such as the Martian meteorites.

How does this relate to Mars?

Aside from the applicability of the infrared technique to geological analyses in a laboratory situation, this technique has a lot to offer when applied in a remote sensing situation. The TES is designed to allow us to analyze rocks passively from orbit. What this means is that instead of seeing the composition of a single fist-sized rock, we can analyze the composition of the surface of an entire planet such as Mars. Therefore, we can use spectra of the Martian meteorites to give us a preview of what TES spectra of Mars may look like. We have measured spectra of several of the ~28 Martian meteorites and studied their characteristic features. As part of this study, we have applied linear deconvolution to see how well we can determine the composition of these rocks from just their infrared spectra. When compared to the known mineral compositions and abundances in the meteorites (as determined by other techniques), we find that we can determine the samples' mineralogies with a reasonably high degree of accuracy. Thus, we are confident that we are able to interpret TES data of Mars in a situation where we do not have other methods of compositional analysis available.

Another reason for acquiring emission spectra of the Martian meteorites is to see if we can use the TES to find out where these meteorites came from on the surface of Mars by identifying a similar spectrum in the Martian dataset. Many scientists would like to know where the meteorites came from on the surface so that they can constrain the mechanisms for the ejection of rock from the planet. Other scientists would like to know what kind of environment the rock came from and what the surrounding rock types are. If we can locate the source region(s) of the meteorites, we can use the meteorites' known ages to learn the actual (rather than relative) age of one or more surfaces on Mars. Our recent survey of the TES data revealed several locations on the surface of Mars that have spectral signatures like those of several Martian meteorites.

Finally, a team of scientists suggested in 1996 that they see structures in one of the Martian meteorites, ALH 84001, that resemble fossil life. Humans have always been fascinated with the idea that life may exist on other planets, and missions to Mars are seeking to establish whether or not that planet had or has a biosphere. Therefore, if we can find it, the source region of ALH 84001 may harbor more information that would answer this question.

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