A diagram of the Nili Fossae Trough on Mars shows an area ripe for remote mineral analysis. The proposed rover landing site is an oval outline at center. Credit: JPL/NASA

Brown team’s Mars site makes short list for 2009 NASA mission

At a Mars landing site selection workshop in California, scientists seeking evidence of past life on the red planet promoted seven potential sites for exploration. Professor Jack Mustard and his team made a strong case for the Nili Trough’s mineral riches.
By Zahra Hirji ’09  |  September 18, 2008  |  Email to a friend

In the hunt for evidence of life on Mars, location is everything. A Brown planetary geology team led by Professor Jack Mustard is betting on a martian region called the Nili Fossae Trough, located in the planet’s northern hemisphere.

Mustard and his team were among seven groups proposing specific sites for the September 2009 Mars Science Laboratory (MSL) mission, the next in NASA’s Mars Exploration Rover series. Planetary scientists have yet to reach agreement on where to send the MSL rover to obtain the most useful results.

On September 15, the MSL mission convened a landing-site selection workshop in Monrovia, California, to narrow the field. By the workshop’s conclusion on September 17, the Brown team had made the cut for the next round of eliminations in November.

Colors represent mineral-rich areas in Nili Trough. (Jack Mustard/Brown University): Colors represent mineral-rich areas in Nili Trough. (Jack Mustard/Brown University) Nili Trough, a Martian mineral treasure-trove located at 21° N, 74.45° E, had fared extremely well at an MSL workshop last year. “We settled on the trough,” Mustard explains, “after scouring the martian landscape for a place that had superb mineral diversity, clear geologic relationships of the terrains that hosted the diverse mineralogy, and a smooth region 25 kilometers in diameter where we could set the rover down.”

This time the seven potential sites were being judged strictly on scientific merit based on four criteria: (1) diversity in geological morphology and mineral composition, (2) a well-established geological record prior to launch, (3) aspects conducive to habitability, and (4) aspects favorable to preserving potential evidence of habitability. Nili Trough ranked high on the first two criteria but lower on the second two, ultimately finishing fifth – good enough to remain in the running.
Bethany Ehlmann, a third-year graduate student on Mustard’s team, explained that workshop attendees represented “two philosophical trains of thought.” Supporters of Nili Trough preferred its mineral diversity, especially its clay and carbonates that indicate water presence and erosion; they did not feel a past standing body of water was needed to prove habitability. Others argued that evidence of Martian life could only be found in a lake or basin area. The top three sites – Eberswalde Crater, Holden Crater, and Gale Crater – are basins, while number four, Marwth Vallis, and Nili Trough are rich in minerals.

Mustard, who is chair of the Mars Exploration Program Analysis Group, emphasized the importance of putting individual site attachments aside in order to determine the optimal place to continue assessing Mars’s habitability.

Attending the workshop in Monrovia with Mustard and Ehlmann were graduate student Leah Roach and postdoctoral student Caleb Fassett.

For now, the Brown geologist and his graduate students will continue to collect Nili Trough data in support of their proposal. “I'm still very excited by what this site presents for understanding Mars as a planet and assessing its habitability,” Mustard notes. In November, the MSL committee will meet to cut the number of potential landing sites from five to three on the basis of engineering constraints. The fourth and final MSL site selection workshop will convene next spring.

For more information about the MSL selection process and results of the third workshop, visit the Marsoweb Web site.