Picking on Mars

Categories: Feature Stories Mars

"It has been a roller coaster ride, let me tell you!" SETI Institute/NASA Ames scientist, Dr. Nathalie Cabrol describes the nerve-wracking process to select a landing site for the NASA’s Mars Expedition Rover (MER) mission.

At a recent interview in the SETI Institute offices, Dr. Cabrol and Edmond Grin, her scientific partner (and husband), relived the ups and downs of their quest; a visit to an ancient dry lake bed at the end of the Ma’adim Vallis, a huge martian drainage channel.

"If something like Ma’adim Vallis (above) is actually a lava flow and looks so much like a fluvial channel, well, we better reassess what we think about the channels we’re seeing on Mars." -Nathalie Cabrol
Credit: R. Irwin III (CEPS/NASM,UVa), T. Maxwell, A. Howard, R. Craddock, D. Leverington

The combined backgrounds of Cabrol and Grin, in planetary geology and hydraulic engineering, give them a special affinity for the site. Each can visualize the ancient and dynamic processes that most likely formed the martian drainage system with its channels cut by flowing water and the lake into which the water emptied. Cabrol and Grin were some of the earliest planetary scientists to recognize the tell tale features of lakes on the Red Planet.

It is not always easy to be first. For nine years (1985-1994) the duo conducted their planetary geology research at the University of Paris-Sorbonne and Observatory of Paris-Meudon, France. Grin assembled a large "Gusev mosaic" of Viking images that stretched across the wall of their office. The martian landscape caught the eyes of NASA scientist Chris McKay, whose 1994 visit to Meudon coincided with the closure of the lab where Cabrol and Grin worked. Cabrol describes the visit as "a defining moment" as it determined their future.

"We left Meudon and followed Chris," she continues. "Edmond packed up the mosaic in his suitcase and we flew to Ames where the mosaic stayed in our cubicle when we arrived and is now archived in our office at the Space Science Division."

With the conviction that Gusev and similar sites were rich with astrobiology potential and thus logical places to visit (ancient lakes are excellent environments for life), Cabrol and Grin pressed on at NASA Ames Research Center, in Mountain View, California. "We had a landing site with no mission," Cabrol explains. What followed was a suite of Mars and Mars-analogue studies supported by several papers on Mars crater lakes. "At the time [between 1994 and 1997], paleolakes were not considered. We had to fight for the notion of crater lakes."

The tide began to turn as the evidence mounted with increases in data resolution, and the community of planetary scientists came to accept the idea of impact crater lakes. Meanwhile, the mandate for Mars exploration had become: "Follow the water!" The timing was right.

A view of Gusev Crater.
Credit: NASA

Thus the MER mission would look for evidence of the past activity of water on Mars, and with the landing site selection process, Cabrol and Grin boarded the "real roller coaster." In January 2001, the first MER landing site workshop, held at NASA Ames, considered a list of 185 potential sites. The preliminary MER landing ellipses, (the landing probability area) were larger than Gusev could accommodate. Knowing this constraint she considered skipping the first workshop altogether.

Realizing that the process "is like voting," and that "if you do not vote, you cannot complain if you do not like the result," she submitted her abstract at the very last minute. On day one, Cabrol presented several sites, including Gusev and Gale Craters both made the first cut. Fortunately, the calibrations determining the size of the ellipse had been refined, and Gusev was now accessible.

Viking image of Gusev Crater, an ancient proposed lakebed that will be targeted in forthcoming Mars Exploration Rover mission.

The "ride" continued. Cabrol recalls another defining moment during the second workshop in October 2001 in Pasadena. This workshop examined safety issues and heard presentations on the sites’ scientific interest. Cabrol pleaded the case of the geologically rich Gusev site. After a first round of votes ten minutes prior to the workshop’s end, Gusev’s chances looked "uncertain." But then safety issues eliminated two very popular Valles Marineris sites. More presentations and discussions preceded a second round of voting. Gusev made it once again. Says Cabrol, "In five minutes we went from deep concern to our candidates selection as one of four primary sites. I began to believe something big was going to happen. It was a very deep experience."

Two more workshops in March 2002 and January 2003 would scrutinize the remaining candidates in detail and take the pair up and down their own emotional peaks and valleys before the April 10th announcement of the two final sites: Meridiani and Gusev. Throughout that year and a half Cabrol happily noted that Gusev research had ceased to be "personal." The research was a community effort involving many scientists and engineers. The community scrutinized all of the sites using new data. When the science selection came through, it was unanimous.

Nathalie Cabrol of NASA Ames Research Center/SETI Institute

If all goes well, soon after landing, MER like a human infant gazing upon its own toes will focus its camera upon the rover’s front wheels then transmit this first image back to Earth. The view from Mars will be immeasurably more exciting as MER transmits its first panorama of the dry and ancient Gusev lakebed.

For Cabrol and Grin, the Gusev studies have been a labor of love that began in 1990, and now, "one revolution of Jupiter later," says Cabrol, "we had consensus of the science team. That was a very rewarding moment". The SETI Institute, which has partnered with NASA since 1998 on Cabrol and Grin’s Mars projects, recently lauded Cabrol and Grin for their work, which represents both the quality and the spirit of wonder that characterizes the interdisciplinary science conducted by the Institute.

"We are not there yet," she reminds us. There are several critical moments, between the countdown, and the moment early in the coming new year when MER opens its ‘eyes’ and transmits the first image to the expectant team at JPL. Nathalie is equally excited and anxious for the second mission, MER B, to the second site (the "Hematite") in Meridiani Planum.

For now, however, Cabrol and Grin are smiling. Asked whether she has an idea of what the panorama will look like, Cabrol answers, "Of course." Asked to describe it she smiles coyly and looks at Grin. "Edmond and I will each make a drawing of what we think the site will look like and compare them after the landing."

After years of meticulous analysis of the site, each has built a vivid mental image of the place but for now they have made a pact not to discuss their respective ideas. Comparing their drawings side by side and with the MER images is a private ritual the two scientists look forward to as a celebration of a successful journey they’ve made together: an exhilarating ride towards Mars.

The Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Mars Exploration Rover project for the NASA Office of Space Science, Washington, D.C. Banner image credit: Artist rendering of Gusev Crater, in a wetter epoch on Mars, used by permission, space4case.com, © Kees Veenenbos.

Related Web Pages

Red Rovers: Returning to Mars
Mars Exploration Website
Two Mars Rover Sites Get Science Stamp of Approval
Evidence for Snow on Mars – and Perhaps an Abode for Life?
Mars Odyssey web site (with new images)
MARIE instrument
Valles Marineris
Mars by Stories
Impact Crater Landing Sites for the 2003 Mars Exploration Rovers
Mars Exploration Rover Homepage
2003 Mars Exploration Rover Mission