John Grotzinger

Chapter 1 · 1970s – 1985 A lacrosse player caught by rocks

Nothing marked John Grotzinger out for geology. At Hobart College, in New York State, he played lacrosse and simply had to fill a requirement in his course of study. He chose a geology class with a reputation for being easy. He never left the subject again.

“Rocks for jocks”

American students call this kind of class “rocks for jocks”: an undemanding science course taken to earn credits. John Grotzinger took it in his third year. He was hooked at once. His professor, Don Woodrow, remembered the student who read the textbook in a room near his office and would burst through the door, full of excitement, to tell him about the geological fact he had just discovered. “It just captured him,” Woodrow said.

There was, however, a famous geologist in his family: his uncle, Preston Cloud, a renowned geologist and paleontologist. But the uncle, the Los Angeles Times reports, found the young man unfocused.

During his studies at Hobart he also did summer research, which he would talk about much later, in 2020, with the college’s president. He earned his bachelor’s degree in geoscience in 1979.

Montana, then Virginia

He went on to the University of Montana, where he earned a master’s degree in 1981, then to Virginia Polytechnic Institute and State University, Virginia Tech, where he received a Ph.D. in geology in 1985. His specialty was taking shape: sedimentology and stratigraphy, the study of how sediments are laid down and stacked in layers, and of what those layers tell us about the environments of the past.

Sources: Hobart and William Smith Colleges, “HWS on Mars,” August 3, 2012, drawing on A. Khan, “Curiosity geologist looks at Mars, finds eerie reminders of Earth,” Los Angeles Times, August 2, 2012 (lacrosse, the “rocks for jocks” course in his third year, Don Woodrow and “It just captured him,” Preston Cloud); Hobart and William Smith Colleges, “Mission to Mars on the Pulteney Street Podcast,” February 3, 2020 (summer research, conversation with Joyce P. Jacobsen); Caltech, Division of Geological and Planetary Sciences, “John P. Grotzinger” page (B.S., Hobart, 1979; M.S., Montana, 1981; Ph.D., Virginia Tech, 1985; sedimentology and stratigraphy).

Chapter 2 · 1985 – 2001 Reading Earth’s oldest rocks

For fifteen years, John Grotzinger studied rocks hundreds of millions, sometimes billions, of years old, to understand how life and Earth’s environment evolved together. Without knowing it, he was preparing for Mars.

Eyes like a wolf

The geologist Paul Hoffman, now a professor emeritus at Harvard, took him along as a field assistant to Canada’s Northwest Territories. He kept one image of him: when John Grotzinger looks at a rock, he “has eyes a bit like a wolf.” In 1992 Grotzinger coauthored a study of the composition of seawater about 1.9 billion years ago, based on carbonates from the Coronation Supergroup, in those same Northwest Territories, and from a group of rocks in Australia.

After a postdoctoral position at Columbia University, from 1985 to 1987, he became a professor at the Massachusetts Institute of Technology, MIT, from 1987 to 2005. There he would hold the Shrock professorship of Earth sciences and direct the Earth Resources Laboratory.

The ocean before animals

His work focused on the Precambrian, the immense stretch of time before animals appeared. In 1993, with James Kasting, he proposed that seawater of that era favored the precipitation of carbonates far more than today, and that it may have contained very little sulfate before 1.9 billion years ago. He was interested in stromatolites, layered structures built by communities of microorganisms, which are among the oldest traces of life.

Timing the Cambrian explosion

The same year, he coauthored in Science, with Samuel Bowring, Andrew Knoll and others, a dating of rocks from northeastern Siberia. The result: the Cambrian began about 544 million years ago, and two of its early stages lasted, together, only five to ten million years. The explosive diversification of animals had therefore been even faster than thought.

To understand that moment, he worked in Namibia and on the subsurface of Oman, sometimes with his family, collecting rocks about 550 million years old. In Namibia he mapped an ancient reef of the Nama Group; in Oman he studied carbonates protected by an envelope of salt. These microbial reefs served as the base for the oldest known animals with calcified skeletons, Cloudina and Namacalathus. He analyzed the carbon isotopes of these rocks to track the great changes in ancient oceans. Over his career he received, among other honors, the Fred Donath Medal of the Geological Society of America, the Henno Martin Medal of the Geological Society of Namibia and the Charles Doolittle Walcott Medal of the National Academy of Sciences, of which he is a member.

Sources: Hobart and William Smith Colleges, “HWS on Mars,” August 3, 2012, drawing on the Los Angeles Times of August 2, 2012 (Paul Hoffman, the Northwest Territories, “has eyes a bit like a wolf, when he looks at a rock,” Namibia and Oman, 550 million years, family, carbon isotopes, MIT Shrock professorship and laboratory, medals, National Academy of Sciences); J. Veizer et al., including J. P. Grotzinger, Geochimica et Cosmochimica Acta, June 1992 (NTRS 19920062098: Coronation Supergroup, about 1.9 billion years); J. P. Grotzinger and J. F. Kasting, Journal of Geology, March 1993 (NTRS 20040090319); S. A. Bowring, J. P. Grotzinger et al., “Calibrating rates of early Cambrian evolution,” Science, September 3, 1993 (NTRS 19940035299); J. P. Grotzinger, reports to NASA, 2002 and 2003 (NTRS 20020045524 and 20030063979: Oman, Namibia, Nama Group, Cloudina, Namacalathus); English Wikipedia, “John P. Grotzinger” (Columbia postdoc 1985–1987, MIT 1987–2005; tertiary source).

Chapter 3 · 2001 – 2006 The layers of Meridiani

In 2001, a friend suggested that John Grotzinger apply to NASA’s Mars Exploration Rover program, Spirit and Opportunity. He was selected. He thought it would be an enjoyable interlude.

Ninety days, he thought

The rover mission was planned to last ninety days. He figured, he told the Los Angeles Times, that it would be fun, and that he would go home after the ninety days.

Opportunity landed in 2004 at Meridiani Planum. The images it sent back showed layered rocks that looked strikingly like those Grotzinger had studied in Namibia, and, in those rocks, small hematite spheres the team nicknamed “blueberries,” clues to ancient water. For geologist Dave Rubin, of the U.S. Geological Survey, the Mars program was lucky to have a sedimentologist like him. He himself would say that the experience stayed with him “forever,” and, in 2020, that this first NASA project “changed my career.”

He also worked on the results from Spirit, which landed in Gusev crater: in 2004 he coauthored a presentation of the first results of its traverse, described with the usual tools of field geology. He also became a participating scientist for the HiRISE camera on Mars Reconnaissance Orbiter.

The move to Caltech

His ties to the California Institute of Technology, Caltech, went back a long way: he was a visiting associate professor there in 1996, then a Moore Distinguished Scholar in 2004. In 2005 he left MIT for Caltech, where he became the Fletcher Jones Professor of Geology. Caltech manages for NASA the Jet Propulsion Laboratory, from which the Mars missions are operated.

Sources: Hobart and William Smith Colleges, “HWS on Mars,” August 3, 2012, drawing on the Los Angeles Times of August 2, 2012 (2001, the friend, the ninety days, Meridiani Planum, the resemblance to Namibia, the hematite “blueberries,” Dave Rubin, “forever”); Hobart and William Smith Colleges, “Digging into the Martian Past with Grotzinger ’79,” January 29, 2020 (Opportunity in 2004, “changed my career”); NTRS 20040057995, “MER Field Geologic Traverse in Gusev Crater, Mars: Initial Results From the Perspective of Spirit,” 2004 (L. Crumpler et al., including J. Grotzinger and M. Golombek); English Wikipedia, “John P. Grotzinger” (MER and HiRISE participating scientist; tertiary source); Caltech, “John P. Grotzinger” page (1996, 2004, Fletcher Jones professorship 2005–2021); SpacePolicyOnline, “NASA Determines Mars Was Habitable,” March 12, 2013 (Caltech manages JPL for NASA).

Chapter 4 · 2007 – 2012 Teaching a robot to do fieldwork

In 2007, John Grotzinger became project scientist for Mars Science Laboratory, the mission meant to put the Curiosity rover on Mars. For the sedimentologist, it was a chance to do what he had always done, but hundreds of millions of kilometers away.

Conductor of the scientists

The project scientist coordinates the work of an international team of nearly five hundred researchers who share the rover’s ten science instruments: cameras, spectrometers, a laser, a drill, analytical laboratories. He was assisted by two deputies, one of them Ashwin Vasavada, of JPL, deputy since 2004.

In a photograph taken on March 5, 2010, he can be seen in JPL’s instrument laboratory alongside director Charles Elachi, project manager Pete Theisinger, Michael Ravine of Malin Space Science Systems, and filmmaker James Cameron, a member of the mast camera team. Together they are watching the motions of an engineering model of that mast.

“If you were the rover, where would you drive?”

To prepare the team, he took it into the field near Death Valley, about 250 miles northeast of JPL, away from the control rooms, to practice field geology. Ashwin Vasavada recalls a 2008 trip on which Grotzinger asked everyone: “If you were the rover, where would you drive?”

He also kept an eye on the tests. In front of a test rover at JPL, he watched the plume of dust raised by the drill and asked the engineers whether that dust could contaminate other instruments.

A two-year delay

The launch, first planned for 2009, was pushed back to 2011. One of his doctoral students, Katie Stack, later said she benefited from the delay: when Curiosity finally landed, she was a senior graduate student, and her advisor, the project scientist, “let me run with my own passions” on the rover team.

Gale, a five-kilometer book

Meanwhile, the scientific community was choosing the site. After five workshops, the choice was announced on July 22, 2011: Gale crater. The site, Grotzinger explained, lies on the boundary between the southern highlands of Mars and the northern lowlands; its low elevation makes it a place where water could have pooled and formed lakes. At its center rises a mountain about five kilometers high made of layers of rock. Those layers read like a book: “You start at the bottom of the mountain and those are the oldest layers.” He compared the landscape awaiting the rover to that of Sedona, Arizona.

Before landing, he had a neglected part of the crater mapped in an original way: the area was divided into sixty-eight squares, and researchers from across the team, including foreign scientists, each mapped one. The edges, he said, mostly lined up.

Curiosity launched on November 26, 2011, and landed in Gale crater on August 5, 2012. The Los Angeles Times then described a fifty-five-year-old man, tall and rangy, with blue eyes often turned toward the ground. His wife, Donna, said the mission had changed the way he worked with others: he had become skilled at building consensus.

Sources: Caltech, “Grotzinger Steps Down as Curiosity’s Project Scientist,” January 15, 2015 (project scientist since 2007); JPL, “New Project Scientist for Mars Rover,” January 5, 2015 (nearly 500 scientists, 10 instruments, Vasavada deputy since 2004); NASA, “Moviemaker with Mars Rover ‘Stunt Double,’” photograph of March 5, 2010; Hobart and William Smith Colleges, “HWS on Mars,” August 3, 2012, drawing on the Los Angeles Times of August 2, 2012 (two deputies, Death Valley about 250 miles away, the 2008 trip and the quotation, the drill and the dust, the 68 squares, age 55, the portrait, Donna Grotzinger); NASA, “Small Steps, Giant Leaps” podcast, episode 52 (Katie Stack Morgan, the delay, the quotation); NASA Science, “Mars Science Laboratory Landing Site: Gale Crater,” July 22, 2011 (transcript of the video narrated by J. Grotzinger: the boundary, the lakes, the 5 km mountain, the book, the quotation, Sedona); E. Lakdawalla, The Planetary Society, July 22, 2011 (the choice, the fifth workshop); K. M. Stack et al., 2013 (NTRS 20150001274: landing on August 5, 2012); English Wikipedia, “John P. Grotzinger” (launch on November 26, 2011; tertiary source).

Chapter 5 · 2012 – 2013 “You would have been able to drink it”

Curiosity’s goal was not to find life, but to say whether Mars could ever have supported it. In less than a year, under John Grotzinger’s scientific leadership, the mission would answer yes.

A slab of city sidewalk

During the first forty days, the mast camera examined two outcrops, “Hottah” and “Link,” through its telephoto lens. They are conglomerates: gravel, from the size of a grain of sand to that of a golf ball, often rounded, cemented into rock. Their shapes and sizes show that they were rolled by water, not by wind. “Hottah looks like someone jack-hammered up a slab of city sidewalk,” Grotzinger said, “but it’s really a tilted block of an ancient streambed.” The discovery was announced on September 27, 2012. “A long-flowing stream can be a habitable environment,” he added, noting that it was not the top choice for preserving organic molecules. So the team kept heading toward Mount Sharp, but it already had, he said, “insurance”: a first potentially habitable environment.

“One for the history books”

In November 2012, the SAM analytical laboratory was studying a soil sample. On November 20, public radio network NPR aired a report in which Grotzinger, without revealing any result, said the data would be “one for the history books.” He also explained the team’s caution: an earlier analysis of the air had seemed to show methane, and they wanted to be sure they were measuring Martian air and not air brought from Earth. The phrase set off a wave of speculation about a discovery of life. On November 29, JPL issued a clarification: “Rumors and speculation that there are major new findings from the mission at this early stage are incorrect,” and the instruments had detected no definitive evidence of Martian organics.

Yellowknife Bay

Curiosity descended about fifteen meters while driving 450 meters east, from its landing site to an area named Yellowknife Bay. There it drilled into a Martian rock for the first time: two slabs of mudstone, a rock made of hardened mud, named John Klein and Cumberland. The analyses revealed about 20 percent clay minerals, ancient water with a near-neutral pH and low salt content, the chemical elements essential for life, and a source of chemical energy used by some microbes on Earth.

On March 12, 2013, at NASA Headquarters, Grotzinger announced the result. “We have found a habitable environment that is so benign and supportive of life,” he said, that if this water had been around and you had been on the planet, “you would have been able to drink it.” Very primitive organisms, he explained, can derive energy just by feeding on rocks. The mission’s main goal had been reached within the first eight months of a mission planned for twenty-three.

On August 2, 2013, for the first anniversary of the landing, he summed up: “We now know Mars offered favorable conditions for microbial life billions of years ago.” Success, he added, had “whetted our appetites to learn more”: the team hoped the layers of Mount Sharp would preserve many other environments.

Younger than expected

On December 9, 2013, with his coauthors, he published the analysis of the Yellowknife Bay layers: the habitable environment had existed at a time “relatively young by Martian standards,” the Hesperian, less than four billion years ago, when parts of Mars were already becoming drier and more acidic. “This habitable environment existed later than many people thought there would be one,” he said. The clays of that era had been thought to have washed in from older deposits; now it was known they could have formed later, which multiplied the places on Mars that could have been habitable.

Sources: NASA/JPL, “NASA Rover Finds Old Streambed on Martian Surface,” September 27, 2012, as reprinted by ScienceDaily (the forty days, Hottah and Link, the gravel, R. Williams, quotations, “insurance”); NPR, “Big News From Mars? Rover Scientists Mum For Now,” November 20, 2012, as summarized in the press (SAM, “one for the history books,” methane); SpacePolicyOnline, “JPL Clarifies Curiosity’s Lack of Historic Discovery So Far,” November 29, 2012 (JPL quotation); K. M. Stack et al., 2013 (NTRS 20150001274: 450 m, 15 m, Yellowknife Bay); D. F. Blake et al., including J. P. Grotzinger, December 2013 (NTRS 20140004215: John Klein and Cumberland, ~20 percent clays, near-neutral pH); K. Chang, The New York Times, March 12, 2013, as quoted by Hobart and William Smith Colleges on March 13, 2013 (quotations, organisms feeding on rocks); NASA, “NASA’s Mars Curiosity Rover Marks First Martian Year with Mission Successes,” June 23, 2014 (mudstone, elements, chemical energy); NASA, “NASA Curiosity Rover Approaches First Anniversary on Mars,” August 2, 2013 (eight months out of twenty-three, quotations); NASA, “NASA Rover Results Include First Age Measurement on Mars and Help for Human Exploration,” December 9, 2013 (Hesperian, quotation).

Chapter 6 · 2014 – 2015 Where there is a mountain, there were lakes

After Yellowknife Bay, Curiosity set off for its main destination, Mount Sharp. For John Grotzinger, it was the great book of layers he had wanted to read since the site was chosen.

On the way

On the way, the rover studied the Windjana sandstones. On June 23, 2014, as Curiosity completed its first Martian year, 687 Earth days, Grotzinger remained cautious: “It’s too early for conclusions, but we expect the results to help us connect what we learned at Yellowknife Bay to what we’ll learn at Mount Sharp.” Windjana still lay within an area where a river had flowed, and it showed signs of a complex history of interaction between water and rock.

At the foot of the mountain

On September 11, 2014, Curiosity reached the base of Mount Sharp. Rather than continuing to Murray Buttes, as planned, the team chose to enter the mountain sooner, near an outcrop called Pahrump Hills. “It has been a long but historic journey to this Martian mountain,” Grotzinger said. The relief there was greater, he explained, and the contact between the base of the mountain and the crater-floor deposits was better exposed.

A series of lakes

On December 8, 2014, he presented the team’s interpretation: Mount Sharp, about five kilometers high, had been built by sediments deposited in a large lake over tens of millions of years. Its layers alternate between lake, river and wind deposits. Rivers carried sand and silt that formed deltas at their mouths, again and again. “We are making headway in solving the mystery of Mount Sharp,” he said. “Where there’s now a mountain, there may have once been a series of lakes.” For the geologist, each return of the lake was a new experiment: “The great thing about a lake that occurs repeatedly, over and over, is that each time it comes back it is another experiment to tell you how the environment works.” In 2015, with the team, he published in Science the study according to which the Gale lakes may each have lasted from tens to hundreds of thousands of years.

Eight days later, on December 16, 2014, NASA announced that Curiosity had measured a tenfold spike of methane in the atmosphere and detected organic molecules in the Cumberland rock powder. “We will keep working on the puzzles these findings present,” he said, asking two questions: could they learn more about the active chemistry causing the methane to fluctuate, and could they choose rock targets where identifiable organics had been preserved?

Handing over

In 2014, Caltech named him chair of its Division of Geological and Planetary Sciences. On January 5, 2015, JPL announced that he was stepping down as project scientist; Ashwin Vasavada succeeded him. “John Grotzinger put his heart and soul into Curiosity for seven years,” said his successor. Grotzinger, who remained a member of the science team, stated: “I have considered it a privilege to help guide the MSL mission for almost eight years.” The mission, he added, had achieved its main goal: finding an ancient habitable environment. And he praised his successor: “Ashwin Vasavada is a great choice as the next project scientist.”

Sources: NASA, “NASA’s Mars Curiosity Rover Marks First Martian Year with Mission Successes,” June 23, 2014 (687 days, Windjana, quotation, the river, the complex history); NASA, “NASA’s Mars Curiosity Rover Arrives at Martian Mountain,” September 11, 2014 (Pahrump Hills, Murray Buttes, quotation, the contact and relief); NASA, “NASA’s Curiosity Rover Finds Clues to How Water Helped Shape Martian Landscape,” December 8, 2014 (5 km, tens of millions of years, lake, river and wind, deltas, quotations); J. P. Grotzinger et al., Science, vol. 350, 2015, cited by A. M. Kling et al., 2016 (NTRS 20170000316: lakes lasting tens to hundreds of thousands of years); NASA, “NASA Rover Finds Active, Ancient Organic Chemistry on Mars,” December 16, 2014 (methane, Cumberland, quotation); Caltech, “John P. Grotzinger” page (division chair 2014–2024); JPL, “New Project Scientist for Mars Rover,” January 5, 2015 (Vasavada, quotation); Caltech, “Grotzinger Steps Down as Curiosity’s Project Scientist,” January 15, 2015 (quotations, the goal achieved).

Chapter 7 · Since 2015 Reading Mars’s history like a book

After Curiosity, John Grotzinger led Caltech’s Division of Geological and Planetary Sciences for ten years. He stayed on the rover team and continued to sign the major studies of Gale.

The discoveries continue

In 2018 he was among the authors of the study published in Science announcing the discovery of organic matter preserved in mudstones about three billion years old at Gale crater. In 2021, as a co-investigator on the CheMin mineralogy instrument, he coauthored a study showing that very salty water from later lakes had seeped into the clay-rich layers and transformed them. These transformations, called diagenesis, can erase the traces of life from the original lake, but they also create the conditions for life underground: “These are excellent places to look for evidence of ancient life and gauge habitability,” he said.

Training, passing on

From 2014 to 2024 he led the division; from 2016 to 2024 he also held its Ted and Ginger Jenkins Leadership Chair. In 2021 he became the Harold Brown Professor of Geology. He teaches sedimentology and stratigraphy, and advanced field geology. Among his former doctoral students, Katie Stack Morgan would become deputy project scientist of the Perseverance rover.

His old college has not forgotten him. Hobart awarded him an honorary doctorate on May 19, 2013; he gave the commencement address there in 2018. In January 2020 he returned to give a lecture. He opened with a question: why is this mission worthwhile? Because of the question of life on Mars. Science, he explained, is a hypothesis, then a plan, then a test: “We have a hypothesis that the earliest history of Mars could have been a place where microorganisms could have survived.” The layers of Martian rock, he said, “can be read like reading a history book.” Curiosity is, for him, the most complicated vehicle humankind has built and sent to space, a summit of systems engineering. And he presented the next mission, Mars 2020, designed to sample the diversity of Mars, search for habitable conditions and signs of past microbial life, and prepare the return of samples to Earth.

Sources: J. L. Eigenbrode et al., including J. P. Grotzinger, “Organic matter preserved in 3-billion-year-old mudstones at Gale crater, Mars,” Science, 2018; NASA, “NASA’s Curiosity Rover Finds Patches of Rock Record Erased, Revealing Clues,” July 8, 2021 (CheMin, brines, diagenesis, quotation); Caltech, “John P. Grotzinger” page (division 2014–2024, Jenkins chair 2016–2024, Brown professorship since 2021, courses); NASA, “Small Steps, Giant Leaps” podcast, episode 52 (Katie Stack Morgan, Perseverance deputy project scientist, former doctoral student of J. Grotzinger); Hobart and William Smith Colleges, “Digging into the Martian Past with Grotzinger ’79,” January 29, 2020 (honorary doctorate of May 19, 2013, 2018 address, the lecture, the hypothesis, “can be read like reading a history book,” the most complicated vehicle, Mars 2020).