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Martian Chronicles: CRISM
By Scott Perl


CRISM Spectra Top .jpg
CRISM Spectra Top
CRISM spectra (top) and image (bottom) of McLaughlin Crater. The warmer colors relate to clay minerals and carbonates.
I’m the Investigation Scientist for the CRISM instrument onboard the Mars Reconnaissance Orbiter (MRO). CRISM is an orbital spectrometer onboard the Mars Reconnaissance Orbiter that has been actively observing the Martian surface since 2006. A spectrometer is a type of “chemical camera” that returns spectral data showing what rocks are made of. CRISM, which stands for the Compact Reconnaissance Imaging Spectrometer for Mars, gives scientists an idea of the composition of rocks and rock formations that we see from orbit. One of the strengths of MRO is that we can observe the same location simultaneously with multiple instruments, including our regular cameras. Joint HiRISE-CRISM observations can give us a three dimensional view of the surface (such as the Endeavour Crater image on the bottom of the page) with mineralogical information attached - what the rocks are composed of and their relative location on some topography.

Digital Terrain Model of Endeavor Crater - Annotated .jpg
Digital Terrain Model of Endeavor Crater - Annotated
Digital Terrain Model of the western rim of Endeavour Crater.
Other Mars missions work with MRO to use our science payload to help them with their own science. CRISM was instrumental in the selection of Gale as the landing site for the Curiosity rover due to its detection of sulfate minerals and clays within the layers of Mt Sharp – both minerals form in different types of water-rich environments.

As a sedimentary geologist, I’m interested in how fluids interact and assist in the formation of outcrops found on the Martian surface. Sedimentary rocks in particular can show a “layer cake” type of deposition, implying that the sediments within those rocks could have been transported and eventually settle, with the more recent (younger) rock layers above the older units. While rovers have the advantage of seeing the small details of the rocks down to the sediments that form them, they are limited to observations over the distance the rover has driven. However, orbiters can put these local details into context by determining what minerals make up the rocks across a wider area, which allows us to better understand the geological history of the area.

CRISM Mineral Parameter Map .jpg
CRISM Mineral Parameter Map
CRISM Red-Green-Blue mineral parameter map. The red corresponds to iron minerals, green to iron / Mg-clay minerals, and blue colors are associated with sulfates. Image is overlain on CTX mosaic.
Not too far from Gale, the MER rover Opportunity is also using CRISM observations to guide their journey. Opportunity is exploring the rim of Endeavour Crater, where CRISM has detected minerals that form in the presence of water. Just as the CRISM image of Gale Crater above uses colors to describe the types of minerals observed, so does this 3-D view of the rim of Endeavour Crater. Here, the red colors show where clay minerals have found, sulfates are in green, and minerals related to volcanic activity are shown in blue. Sulfate minerals and clays, just as on Earth, are diagnostic of geochemical processes that involve liquid water.

As CRISM and MRO continue its global science investigations we look forward to discovering areas of the planet that have been influenced by ancient surface water and by more present fluid activities.Together with the regional investigations that Opportunity and Curiosity continue to build we as the scientific community anticipate future discoveries that pertain to a better and clearer picture of the surface of Mars, both past and present.

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