CRISM (Compact Reconnaissance Imaging Spectrometer for Mars)
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Geoffrey Brown, Johns Hopkins Applied Physics Laboratory
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January 23, 2014

Ten Years of Opportunity and Groundbreaking Mars Science

As NASA’s Opportunity Rover Marks its Tenth Anniversary, CRISM Continues to Show the Way for Past, Present, and Future Mars Rovers

Two students looking down talking about their project.

NASA's Mars Explorer Rover Opportunity (artist rendering, left) marked its tenth year of operations on Mars this week with new findings at Endeavour Crater, made thanks to data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the Mars Reconnaissance Orbiter (artist rendering, center). CRISM also helped select the landing site for the Curiosity rover (photo mosaic, right), which landed on Mars in 2012.
Credit: NASA/JPL-Caltech

The tenth anniversary of NASA’s Mars Exploration Rover (MER) Opportunity's landing, on Jan. 24, 2004, marks what has become an unprecedented catalog of discoveries and findings about the Red Planet. The achievements of the two MERs (Opportunity’s twin, Spirit, ceased operations in 2010), sometimes operating with guidance from the Mars Reconnaissance Orbiter (MRO, launched in 2005), have helped rewrite our knowledge of Mars and its history.

A new paper, published today in the journal Science, details new findings made on the rim of the Endeavour Crater that were made possible through unparalleled coordination between planetary assets – Opportunity roving on Mars' surface – and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), flying overhead on MRO. These new findings show that water altered rocks on Endeavour’s rim both before and after formation of the crater, roughly four billion years ago. This was a time of both sustained asteroid impacts, and also of persistent liquid water – present both before and after the impact that created a 14-mile (22 kilometer) radius crater. The particular mineral fingerprints left behind by this water tell scientists something even more important: that the water present before the crater formed was neutral to slightly acidic, and potentially suitable for life.

“These conditions would have been much more habitable as compared to” conditions at later times recorded by younger rocks around the crater, says Washington University in St. Louis’s Raymond Arvidson, lead author of the paper and Deputy Principal Investigator for Opportunity, as well as a Co-Investigator on CRISM. “The use of CRISM along-track oversampled (ATO) observations to identify and map relatively small outcrops on the Cape York rim segment of the Endeavour Crater, when combined with directing Opportunity to those locations for detailed surface measurements, allowed us to decipher aqueous [watery] environments that predate formation of the crater.”

CRISM, built by the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Md., has been a primary tool used by scientists working to provide a more accurate image of ancient Mars. Often operating in tandem with rovers – whether to help to choose a landing site (as for the Mars Science Laboratory/Curiosity rover), or to guide the Opportunity rover to geologic targets which show evidence of past water activity – CRISM has played a major role in reshaping our current understanding of the history of water on Mars, a picture that differs drastically from what was imagined just 15 years ago.

“CRISM and the other instruments on MRO have truly revolutionized the thinking about Mars’ surface evolution,” says APL’s Kim Seelos, research scientist and member of the CRISM mission operations team. “Before CRISM and OMEGA [another spectrometer on board the European Space Agency’s Mars Express mission, launched in 2003] Mars was thought always to have been a dry, basaltic planet – a let-down based on expectations from all the great morphologic evidence of flowing water and interesting geology.  But now we are able to see a hugely complex past that hosted different watery environments and areas of alteration and deposition, including activity right up to present day.  It’s fascinating. This new paper is just one of many contributions that CRISM has been able to make to our understanding of Mars.”

CRISM has been hard at work above Mars since 2006; the operations team at APL is constantly coming up with new and inspired ways to get more and better data out of the spectrometer, which “sees” different minerals left behind by past water on Mars. The relatively new ATO mode provides a marked improvement in resolution.

“This way of acquiring data takes advantage of CRISM’s gimbal, or pivoting system, to scan across the surface of Mars a bit faster than we normally do to take out spacecraft motion,” says Seelos. “The gimbal pivots in the direction that the spacecraft is moving, and the modified pivoting increases spatial resolution in the ‘along-track’ direction. The result is that individual pixels in an ATO image are reduced in size from roughly 18 meters down to five to eight meters. Opportunity’s science team would not have known that this extremely interesting exposure of ancient minerals was worth exploring if not for orbital data from CRISM.”

This new ATO mode, along with CRISM's tens of thousands of previous images, provides new exploration targets for Mars scientists and rovers. “New CRISM observations are currently being used to help plan the next phases of Opportunity’s mission in rim segments to the south of Cape York,” says Arvidson. “Results from analyses of CRISM data have also been and will continue to be crucial to directing the Curiosity rover to key locations near and on Mount Sharp.”

One location in particular, according to Arvidson, is of particular interest and is cited in the results published today. “The new excitement,” he says, “is that a possible niche for microbes may be preserved in hematite-bearing rocks capping a ridge to the north of Mount Sharp. Those rocks may record both favorable water chemistry and even a chemical energy source. On Earth, microbes favor the type of environment indicated at this location, and these discoveries have raised the level of excitement within the science teams on both rovers for making detailed measurements to better understand which environments were habitable.”

As CRISM and the scientists analyzing its images unlock more of Mars’ past climate mysteries, data from the instrument guides the two existing rovers and contributes to the selection of where to send the next rover. “We also look forward to both new observations and mining the terabytes of existing CRISM data to help identify the best landing sites for the NASA Mars 2020 rover mission,” says Arvidson.

-  Geoff Brown

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