For 20 years, Robots Have Inhabited Mars. What Keeps Them Humming?

This year marks a significant milestone in the exploration of our solar system. NASA has had wheels on the ground of Mars every day during the last two decades. Beginning with the landings of the Spirit and Opportunity rovers in January 2004, a lineage of increasingly sophisticated mobile and stationary robots—Phoenix, Curiosity, InSight, and Perseverance—have explored the Red Planet, pushing themselves to their operational limits.

These missions have changed our perceptions of the Red Planet, says space historian Matthew Shindell in his recently published book, For the Love of Mars: A Human History of the Red Planet. Shindell, a curator of planetary science and exploration at the National Air and Space Museum, says that the “Red Planet went from being an extreme desert version of Earth to being a planet that a seemingly separate evolutionary path had rendered still and lifeless.’’

In the following excerpt from his book, Shindell looks back at the accomplishments of the past 20 years, when NASA’s plucky robotic explorers became the new heroes of the Space Age and paved the way for future human exploration of Mars.

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On February 12, 2019, a team of engineers at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, sent one final set of commands to the Mars Exploration Rover (MER) Opportunity. Affectionately nicknamed “Oppy,” the rover had been exploring Mars for 15 years. It had proven itself to be a resilient robotic adventurer, surviving broken wheels, sand traps, and the harsh Martian climate. But now it had been unresponsive for months. Its final message to Earth arrived on June 10, 2018, on the eve of a giant dust storm that darkened the Martian sky.

The storm, which Oppy had first detected at the end of May, grew dense enough to cut off sunlight to the rover’s solar panels. The mission team hoped that Oppy could ride out the storm in hibernation mode, using minimal power to keep itself warm. But the final downlink indicated that the rover’s battery was close to dead. To those who worked with her, Oppy wasn’t an “it” but a “she,” and they knew that without battery power, she would have no way of protecting her aging circuits from the cold.

The final transmission from the rover noted that the high levels of dust in the atmosphere had turned the sky dark. The dust storm lasted for two months, and during this time JPL received none of the automated pings from Oppy that mission controllers were expecting.

They didn’t give up all hope, but they knew that her battery had most likely died. They watched as robotic spacecraft in orbit around Mars tracked the storm, waiting to see the surface features of the planet emerge from the cloud of dust. As the Martian sky finally cleared toward the end of June, JPL engineers expected that it could take months for Oppy’s solar panels to recharge her. But one final problem presented itself: Oppy’s solar panels were blanketed with dust, unable to generate sufficient power to bring the rover back online. Though they tried for eight months to revive her, the mission controllers eventually had to let her go.

When the news spread that NASA was giving up on reaching Oppy, the science writer Jacob Margolis translated the rover’s last bit of data (with some poetic license) into the message, “My battery is low and it’s getting dark,” and posted it on Twitter (now known as X). Oppy’s “last words” were quickly made into memes and cartoons that were tweeted and posted widely on the internet. Along with these came heartfelt thank-yous for the many years of exploration and discovery. The well-wishings came not just from those who had designed, built, or operated the rovers, but from people who had enjoyed hearing about the discoveries made on Mars.

For some who had grown up with Oppy on Mars, losing the rover was like losing a piece of their childhood. Margolis remembered first being shown the rover’s images as a kid: “I was enraptured by the promise of NASA’s most ambitious rover mission yet and that we could potentially confirm that water, and maybe even life, once existed there. It’s one of my favorite science memories.”

Many of Oppy’s mourners perhaps knew very little of the esoteric knowledge the rover helped collect, but nonetheless were impressed by Oppy’s seeming tenacity. They were probably inspired by the dramatic horizons captured by her panoramic imaging system or they had enjoyed her occasional selfies atop rocky outcrops. As NASA had learned over the previous quarter century, the public engages with rover missions in ways not inspired by flyby or orbiter missions, and the desert-like landscapes of Mars, even if devoid of alien civilizations, can be used to evoke romantic notions of exploration and discovery. The public mourning of Oppy speaks to an expectation that robotic exploration of Mars is connected to the human future—to human exploration of Mars, or even human settlement.

Intrepid Explorers

When a rover lands on Mars, it demonstrates the incredible feats nations can accomplish when government funding, political will, and technological know-how are aligned with national priorities. Among other things, it demonstrates an impressive level of technocratic ability and organizational power. For the United States, sending missions to Mars has typically been an occasion for great fanfare. These occasions are by design meant for global consumption, as are the events surrounding arrival at Mars and the descent to the surface.

During the Cold War, these moments were one way of providing a civilian face for space technology and infrastructure while demonstrating the capabilities of these technologies through peaceful means. Even though the Cold War context for space exploration no longer exists, these displays of techno-scientific gymnastics have not become irrelevant. The U.S. continues to use space as an arena in which to show off its economic and technological might, to build alliances, and to compete with adversaries. These moments are still used to legitimate political claims of global leadership—in space and on Earth.

Since 1997, because of longer-lived spacecraft and a mostly continuous stream of missions, Mars exploration has been a largely uninterrupted activity introducing a new cast of orbiters, landers, and rovers. This enterprise has produced more data, in more spectral wavelengths and at higher resolution, than was achieved in the first decades of exploration. It has transformed Mars into a known world—one that still holds questions, to be sure. The orbiting missions have done the lion’s share of the science, at least when it comes to geographic coverage and description of planetary-scale phenomena.

But it’s the landers, and especially the rovers, that have engaged the public imagination. The fact that this exploration has been done robotically, without human “boots on the ground,” has not, by and large, dampened the public’s appetite for exploration—an appetite fed by new media that provide constant access to images and stories and which encourage followers to imagine themselves in the Martian landscape.

The robots themselves are often presented as intrepid explorers, reminiscent of an earlier era of terrestrial exploration and the romantic notions that went along with it—one in which human explorers risked their lives to reach the inhospitably extreme environments of the North and South Poles. 

Oppy’s “last words” recall those of the seasoned adventurer Lawrence Oates, who died on Robert Scott’s Terra Nova expedition to the South Pole (1910–13). Suffering from frostbite and gangrene, Oates knew that his lingering on was only putting the other members of the expedition at risk. He walked out of his tent into a blizzard, telling his crew, “I am just going outside and may be some time.” Scott interpreted this act of self-sacrifice as the ultimate example of a British army officer’s bravery and resolve.

Or consider another arctic explorer, Alfred Wegener—famous today as the originator of the theory of continental drift—who died in Greenland in 1930 while attempting to resupply his expedition. He had insisted that exploratory science demanded heroics. Clues to the inner workings of the universe were, he believed, much more significant than himself. His men built an ice-block mausoleum around him, with a large iron cross to mark the grave. Like Oates and Wegener, Oppy now rests in the spot where her exploration ended. Rovers and their imaging systems have made Mars seem closer than ever before and have allowed even greater fidelity in our imaginings of humans on Mars.

Managing Martians

The Spirit and Opportunity rovers survived much longer than expected, and in the process were able to cover much more ground and do a lot more science than originally anticipated. Spirit traveled five miles over its seven years on the planet, while Opportunity covered just over 28 miles over 14 years.

Launched on November 26, 2011, Curiosity landed in Gale Crater on August 6, 2012. The landing site, a 96-mile-wide impact crater, was selected on the basis of infrared data that indicated the crater might once have held a large lake. At the site, science teams using Curiosity’s instruments confirmed that the floor of the crater contained clays and sulfates. The rover spent several years ascending a three-mile-tall mound of sedimentary debris nicknamed Mount Sharp (officially named Aeolis Mons) and studying its mineralogy one layer at a time.

The science teams speculated that the base of the mound was the remnant of sediment laid down over perhaps as many as two billion years by a lake that once filled the crater. Some have proposed that the lake was a temporary but recurring body of water created by a series of flash floods. The minerals and their presence in Mount Sharp speak to a time when Mars’ climate was saturated with water. The science teams are still trying to get these layers to tell them when and why Mars became the dry world we know today.

Other spacecraft have followed. InSight arrived in late 2018 carrying instruments to detect Marsquakes and subsurface temperatures. Most recently, in February 2021, NASA’s Perseverance rover landed in Jezero crater, another site on Mars suspected to have held an ancient lake. The feature that most attracted scientists when selecting this landing site was what appears to be a river delta where sediments from water flowing into a lake within the crater were deposited.

Perseverance, similar to Curiosity in many ways, is specifically tuned to look for biosignatures—signs that life might once have enjoyed Mars’ warmer, wetter past. For the first time, it carries a drill that can collect rock core samples that NASA plans to retrieve and send back to Earth in a series of future robotic missions. It also carried a successful technology demonstration: a small autonomous rotorcraft, or Mars helicopter, named Ingenuity (see “The Little Copter That Could”), which captured the imagination of a world still in the throes of a pandemic. We may see increasingly capable helicopters sent to Mars in the future.

Landers and rovers enable humans to replay the history of terrestrial exploration on another world. These spacecraft are tools, of course—not explorers in their own right. The explorers are on Earth, in large teams of scientists and engineers from universities and research centers around the world.

Who are these Mars explorers? Within the story of Mars exploration, Donna Shirley, who joined JPL in 1966 as one of its few women engineers (and the only one with an engineering degree), served as development lead of the Pathfinder mission and then went on to become the manager of the lab’s Mars Exploration Program. In 1998, Shirley published Managing Martians, a memoir of her time at JPL, which describes her path from engineering student to leader of a team of 30 engineers designing Sojourner and making the rover a reality.

The charismatic scientists who managed to catch the public’s eye in the 1990s put forward an image of Mars exploration that was a far cry from the “cool militarism of the old Cold War space program” and instead presented the new model of “nerds in love.”

At their best, Mars memoirs convey a level of enthusiasm about exploration and the production of knowledge that is difficult to find in more academic histories or ethnographies of Mars exploration. They’re also much more personal than those academic accounts. The astrobiologist Sarah Stewart Johnson’s The Sirens of Mars: Searching for Life on Another World (2020) delivers a well-curated chronology of previous eras of Mars exploration and recounts the stories of those whose passions and research have informed her own thinking about the Red Planet, as she applies the still young science of extremophiles to the question of life on Mars.

The people she describes in her book are kindred spirits: Some are from past eras, peering at the fuzzy red disk of Mars through observatory telescopes or from hot-air balloon gondolas, and others are contemporaries working alongside her in university laboratories or at far-flung field sites. In their stories she finds the “great strides forward, the longing for answers.” Johnson’s account is one of a participant in history, of being among the first cohort of women to explore Mars.

Two Futures

Toward the end of the first quarter of the 21st century, at least two futures for Mars seem to lie ahead. One path leads to a Mars that remains distant from human activity. Scientists and engineers will likely find new ways of exploring this Mars and drawing from it the secrets of its past. Perhaps they will find some form of Martian life or evidence that it once existed. Perhaps they will uncover planetary knowledge or new technologies that will help abate or alleviate the impacts of climate change. It’s even possible that this extended period of interest in Mars science will wane, replaced by missions to the icy ocean moons of the outer planets. All of this can happen without one human ever setting foot on Mars.

The other path leads to humans on Mars. We don’t yet know exactly what this future will look like—whether it will be small-scale scientific expeditions, an orbiting Mars station, or full-scale efforts to build new communities or even cities on Mars. Perhaps all of these things can happen, and perhaps one will lead to the others.

At present, however, there is no solid plan for such endeavors. It’s possible that the success or failure of the currently planned Artemis missions to the moon will at least partially determine the fate of a human Mars. Will NASA and its partners succeed in building a sustainable presence on the moon? Or will we find ourselves living through another Apollo: another impressive technological spectacle that is abandoned when the goal is reached and the price has grown too high? There is no agreed-upon answer to the question of what ends these efforts at the moon, let alone Mars, will serve. Who will benefit from a human presence on Mars? Will these journeys serve a larger purpose, such as developing new technologies that help us live better on Earth? Or will they be used to extract new wealth from a new environment? Will they lead to a utopia, a dystopia, or something in between?

Meanwhile, NASA’s most recent Mars rover, Perseverance, is meant to pave the way for human exploration of Mars. Not only is it collecting rock samples to be sent back to Earth by follow-on robotic missions for laboratory analysis—work that will no doubt help in better characterizing the Martian environment and in determining what will be required to keep humans alive there—but it also carries experiments directly related to human needs.

One experiment, the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE), first proposed in the early 2000s, has shown that oxygen can be produced from the planet’s carbon dioxide-rich atmosphere. Oxygen is, of course, required for humans to breathe, but it is also a component of rocket fuel that could be used for the return journey to Earth. Spacesuit materials can also be found on the Perseverance rover, and another experiment is recording how those materials hold up to the Martian elements over time. While these components don’t add up to a fully realized map to Mars, one can imagine how each is an incremental step toward the planet.

We can call Mars the most Earth-like planet in our solar system. And yet Mars remains distinctly uninhabitable—or at least very inhospitable. The surface is cold and constantly bombarded by radiation; the atmosphere is incredibly thin and made up mostly of carbon dioxide. The soil, if we can call it soil, is toxic to anything we would want to grow there, and the dust storms that occasionally cover the entire planet carry a very fine powder that would damage skin, eyes, and lungs. In short, for the first astronauts on a return trip to Mars, the Red Planet would be one of the most hazardous worksites ever attempted.

For anyone who tried to live on the planet in the long term, Mars would present more challenges than the most remote and hostile places on Earth. And yet so much of the discourse surrounding Mars today treats the planet as a new frontier—a territory filled with nothing but wide-open spaces waiting to be transformed by the human hand.

Right now, the idea of going to Mars does not dominate our culture. It mostly belongs to small communities of experts and enthusiasts. It has a larger cultural resonance, as it has for centuries, because it allows us to tell stories about ourselves that engage the imagination. This is as true about technical plans for Mars expeditions as it is about science fiction novels, films, and television series.

If and when we do go to Mars, it will by necessity be such a massive undertaking that it will become one of the largest technological and cultural projects of its time. It will both shape and enact ideas about ourselves and our relationships to each other, our world, and the cosmos. For this reason, I think the most important question we can ask now is not “How will we get to Mars?” but “Who do we want to be when we become Martians?”  

Reprinted with permission from For the Love of Mars: A Human History of the Red Planet by Matthew Shindell. Published by the University of Chicago Press, © 2023. All rights reserved.

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Matt Shindell curates the National Air and Space Museum’s collection of spacecraft, instruments, and other artifacts related to the exploration and study of the solar system.

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This article is from the Spring 2024 issue of Air & Space Quarterly, the National Air and Space Museum's signature magazine that explores topics in aviation and space, from the earliest moments of flight to today. Explore the full issue.

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