NASA’s long road to Gale Crater

If Gale Crater isn’t your favorite choice for a landing site for NASA’s next Mars rover, you can’t claim the choice was made hastily. The international community of Mars scientists thoroughly sifted the Red Planet to find a feasible landing site for the Mars Science Laboratory (MSL) rover, dubbed Curiosity. It is due to launch in late November 2011 and will arrive at Gale Crater in August 2012.

OUT OF MANY, ONE. All the 59 sites considered as landing places for the Mars Science Laboratory appear on this Mars map. Initially, the band from 45° N to 45° S (dotted white lines) was considered safe and feasible from the engineering viewpoint. These bounds were later narrowed to 30° N and S (solid white lines). The Final Four candidates are in blue; the winner - Gale Crater - is number 54, located toward the right edge. (Figure 3 from the paper.)

MSL’s mission is to look for a geologic environment (or set of environments) that would support microbial life, past or present, and which could be assessed by the rover’s instruments. Scientists held five workshops between 2006 and 2011 to identify potential sites — a search that turned up a total of 59 individual landing sites, each of which was examined carefully.

The process of how scientists converged on a small group of suitable sites is described in a recent paper in Planetary and Space Science by John Grant (National Air and Space Museum) and colleagues. Grant headed the search effort along with the Jet Propulsion Laboratory’s Matt Golombek, also a co-author on the paper.

While engineering constraints, plus snags in technology development, imposed latitude and altitude limits for potential sites, in the end all of the Final Four sites (Eberswalde Crater delta, Gale Crater, Holden Crater, and Mawrth Vallis site 2) came out equal from an engineering perspective. It was science that drove the choice.

At the first workshop, 35 sites were proposed, debated, and ranked. The second tackled 50 sites (many of them new), and came up with a short list of six. A seventh site was added at the third workshop, from which emerged the Final Four. The last two workshops sharpened the picture of these sites, using new data from Mars Odyssey, Mars Reconnaissance Orbiter, and Mars Express. (The fifth workshop, in May 2011, had not yet occurred when the paper was completed.)

To leave NASA and the MSL project with a free hand to choose among the candidates, the last workshop reviewed all the data and summed up the pros, cons, and uncertainties of each site — but deliberately made no recommendation. About a month later, on June 24 NASA announced that the four sites had been narrowed to two (Gale and Eberswalde), and on July 22, the space agency announced the final choice of Gale as the landing site for the Mars Science Laboratory.

It should be a spectacular place to explore.

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