John Grotzinger folds his rangy frame into a plastic leather booth at Conrad’s, an unassuming diner in Pasadena, California. It is nearly midnight, and a smattering of customers have drifted in for a late-night snack. In the booth on one side, members of a Neil Young tribute band relax after a gig; on the other, a personal-trainer-cum-actor is winding down from a script reading.

But Grotzinger, who is chief scientist for NASA’s Mars Science Laboratory mission, is trying to gear up for the start of his working day at the nearby Jet Propulsion Laboratory, as the rover Curiosity begins its fourth Martian day. Still riding the high of the rover’s triumphant landing on 6 August, Grotzinger says that he is “overjoyed” with the landing site, a level plain between the rim of Gale Crater and Aeolis Mons, the imposing mountain at the crater’s centre. But he is sobered by the demands of managing such a complicated machine and the 400-strong science team behind it. “I feel the burden of two-and-a-half billion dollars,” says Grotzinger, a geologist at the California Institute of Technology in Pasadena. “I feel the burden of the future of Mars exploration.”

Grotzinger’s job is to get the maximum scientific pay-off from that investment during the two years or more that the rover is expected to remain active. His day will begin at 12:42 a.m. with a science discussion with the principal investigators for the rover’s ten instruments. But first Grotzingerneeds breakfast and some coffee. One cup will do: the excitement of new data, which are expected in a downlink in two hours’ time, will be enough to keep him alert.

P. E. Alers/ NASA

Grotzinger was a regular at Conrad’s in 2004, before and after his working days on the rover Opportunity, which landed that year along with Spirit, its twin, comprising the Mars Exploration Rover mission. Because the rovers were positioned on opposite sides of Mars, one team would be having breakfast while the other would be eating dinner. “The waitresses were always confused,” he recalls. This time there is only one rover, but still no standard working day. Adapting to ‘Mars time’ requires starting each Earth day 40 minutes later than the last to match Martian daylight, inducing a state of perpetual jet lag.

Grotzinger is already marshalling different opinions on where the rover should go for its inaugural drive, expected to take place in the next week. The first images from the rover’s navigation cameras suggested one possibility when they revealed whitish linear features in a shallow trench scoured out by the blast of the landing system’s retrorockets. The lines could be fractures filled with water-altered minerals — key targets for exploration in the mission’s goal of assessing whether ancient Mars could have supported life. “We want to find out if we’ve got a bird in the bush right there,” Grotzinger says.

Several hundred metres away is a second option for exploration: a five-metre-high slope, or scarp, that separates the dusty desert pavement on which the rover landed from the more hummocky terrain that lies beyond. The scarp marks the edge of materials deposited at the foot of an alluvial fan, a sedimentary feature left behind from floods that once spilled down from the rim of Gale Crater. The materials seem to be cemented or consolidated in some way, and layers exposed on the scarp might reveal the comings and goings of an ancient lake.

Away in the distance is the rover’s ultimate destination: the 5.5-kilometre-high Aeolis Mons, dubbed Mount Sharp by the science team, which casts a long shadow over the rover each morning. Data from orbiting spacecraft suggest that deposits on the mountain’s lower shoulders were formed in water — and for now at least, these deposits represent the team’s best chance of working out whether microbes could have lived on Mars billions of years ago.

Managing the tension between short-term and long-term goals will be a constant challenge for Grotzinger, says Raymond Arvidson, deputy principal investigator for the Spirit and Opportunity rovers and a planetary scientist at Washington University in St Louis, Missouri. “Do we stop and smell the roses or do we button up and continue to the next outcrop?”

Colleagues say that, in his geological field studies on Earth, Grotzinger balances both tendencies, displaying an exuberant fitness that carries him across wide terrain even as he keeps an eye on the minutiae of mineralogy and texture. He scrambles like a mountain goat, says Ralph Milliken, a former postdoctoral student of Grotzinger’s and now a planetary scientist at Brown University in Providence, Rhode Island. Yet Andrew Knoll, a palaeontologist at Harvard University in Cambridge, Massachusetts, recalls a field trip with Grotzinger to Siberia in the early 1990s, during which the geologist discovered small pieces of volcanic breccia rock underfoot that had gone unnoticed by Knoll, no slouch of a field geologist himself. By dating those rocks, the researchers were able to pin down the timing of the Cambrian boundary better than ever before, and show that the Cambrian explosion of animal life happened incredibly quickly (S. A. Bowring et al. Science 261, 1293–1298; 1993).

Having an eye for detail and a gift for stratigraphic field work will certainly help Grotzinger to decode Mount Sharp and the millions of years of history that its layers represent. But he faces sociological challenges as well as scientific ones. Unlike Steven Squyres, the charismatic planetary geologist from Cornell University in Ithaca, New York, who was principal investigator for Spirit and Opportunity, Grotzinger does not have final authority over plans for the rover. Instead, as project scientist, he heads an executive committee that is made up of a representative from NASA headquarters and the principal investigators for the ten instruments. “He appreciates that he’s the head of a committee, and not the Pope,” says Knoll.

Arvidson says that Grotzinger is already aware of the job’s limitations. “John’s working the crowd,” he says. “He really understands that in order to get buy-in, you have to establish trust.”

One exercise that Grotzinger is proud of is a crowd-sourced geological map of Curiosity’s landing ellipse that was put together before touchdown. Recognizing that little was known about the fine-grained detail of the location, he divided the ellipse into 151 quadrangles, measuring roughly 1.6 kilometres on each side, and asked for volunteers from the science team to turn orbiter data into geological maps of each sector. It was partly a team-building effort in the lead up to the landing — how better to bring opinionated geologists into the fold than by working on a patchwork quilt? But he also wanted to show the wider team that the landing terrain was full of intriguing detail that should not be overlooked in a fast trek to Mount Sharp.

“There is going to be something for every­one,” says Grotzinger, slurping his coffee and smiling. “I quoted Bob Dylan when I was talking to these guys … ‘A lot of people don’t have much food on their table. But they got a lot of forks ’n’ knives. And they gotta cut somethin’.’ If you have an empty plate, people are going to go for each other. But if there’s a wealth of riches, we can all share.”