As a mere earthling, I remember watching in fascination as
Sojourner sent back photos of the Martian surface during the summer of 1997. I was not alone. The servers at NASA’s Jet Propulsion Lab slowed to a crawl when they got more than 47 million hits (a record number!) from people attempting to download those early images of the Red Planet. To be fair, it was the late 1990s, the Internet was still young, and most people were using dial-up modems. By the end of the 83-day mission, Sojourner had sent back 550 photos and performed more than 15 chemical analyses of Martian rocks and soil.
Sojourner, of course, remains on Mars. Pictured here is Marie Curie, its twin. Functionally identical, either one of the rovers could have made the voyage to Mars, but one of them was bound to become the famous face of the mission, while the other was destined to be left behind in obscurity. Did I write this piece because I feel a little bad for Marie Curie? Maybe. But it also gave me a chance to revisit this pioneering Mars mission, which established that robots could effectively explore the surface of planets and captivate the public imagination.
Sojourner’s sojourn on Mars
On 4 July 1997, the
Mars Pathfinder parachuted through the Martian atmosphere and bounced about 15 times on glorified airbags before finally coming to a rest. The lander, renamed the Carl Sagan Memorial Station, carried precious cargo stowed inside. The next day, after the airbags retracted, the solar-powered Sojourner eased its way down the ramp, the first human-made vehicle to roll around on the surface of another planet. (It wasn’t the first extraterrestrial body, though. The Soviet Lunokhod rovers conducted two successful missions on the moon in 1970 and 1973. The Soviets had also landed a rover on Mars back in 1971, but communication was lost before the PROP-M ever deployed.)
This giant sandbox at JPL provided Marie Curie with an approximation of Martian terrain. Mike Nelson/AFP/Getty Images
The six-wheeled, 10.6-kilogram, microwave-oven-size
Sojourner was equipped with three low-resolution cameras (two on the front for black-and-white images and a color camera on the rear), a laser hazard–avoidance system, an alpha-proton X-ray spectrometer, experiments for testing wheel abrasion and material adherence, and several accelerometers. The robot also demonstrated the value of the six-wheeled “rocker-bogie” suspension system that became NASA’s go-to design for all later Mars rovers. Sojourner never roamed more than about 12 meters from the lander due to the limited range of its radio.
Pathfinder had landed in Ares Vallis, an assumed ancient floodplain chosen because of the wide variety of rocks present. Scientists hoped to confirm the past existence of water on the surface of Mars. Sojourner did discover rounded pebbles that suggested running water, and later missions confirmed it.
A highlight of Sojourner’s 83-day mission on Mars was its encounter with a rock nicknamed Barnacle Bill [to the rover’s left]. JPL/NASA
As its first act of exploration,
Sojourner rolled forward 36 centimeters and encountered a rock, dubbed Barnacle Bill due to its rough surface. The rover spent about 10 hours analyzing the rock, using its spectrometer to determine the elemental composition. Over the next few weeks, while the lander collected atmospheric information and took photos, the rover studied rocks in detail and tested the Martian soil.
Marie Curie’s sojourn…in a JPL sandbox
Meanwhile back on Earth, engineers at JPL used
Marie Curie to mimic Sojourner’s movements in a Mars-like setting. During the original design and testing of the rovers, the team had set up giant sandboxes, each holding thousands of kilograms of playground sand, in the Space Flight Operations Facility at JPL. They exhaustively practiced the remote operation of Sojourner, including an 11-minute delay in communications between Mars and Earth. (The actual delay can vary from 7 to 20 minutes.) Even after Sojourner landed, Marie Curie continued to help them strategize.
Initially, Sojourner was remotely operated from Earth, which was tricky given the lengthy communication delay. Mike Nelson/AFP/Getty Images
During its first few days on Mars,
Sojourner was maneuvered by an Earth-based operator wearing 3D goggles and using a funky input device called a Spaceball 2003. Images pieced together from both the lander and the rover guided the operator. It was like a very, very slow video game—the rover sometimes moved only a few centimeters a day. NASA then turned on Sojourner’s hazard-avoidance system, which allowed the rover some autonomy to explore its world. A human would suggest a path for that day’s exploration, and then the rover had to autonomously avoid any obstacles in its way, such as a big rock, a cliff, or a steep slope.
JPL designed
Sojourner to operate for a week. But the little rover that could kept chugging along for 83 Martian days before NASA finally lost contact, on 7 October 1997. The lander had conked out on 27 September. In all, the mission collected 1.2 gigabytes of data (which at the time was a lot) and sent back 10,000 images of the planet’s surface.
NASA held on to
Marie Curie with the hopes of sending it on another mission to Mars. For a while, it was slated to be part of the Mars 2001 set of missions, but that didn’t happen. In 2015, JPL transferred the rover to the Smithsonian’s National Air and Space Museum.
When NASA Embraced Faster, Better, Cheaper
The
Pathfinder mission was the second one in NASA administrator Daniel S. Goldin’s Discovery Program, which embodied his “faster, better, cheaper” philosophy of making NASA more nimble and efficient. (The first Discovery mission was to the asteroid Eros.) In the financial climate of the early 1990s, the space agency couldn’t risk a billion-dollar loss if a major mission failed. Goldin opted for smaller projects; the Pathfinder mission’s overall budget, including flight and operations, was capped at US $300 million.
In his 2014 book
Curiosity: An Inside Look at the Mars Rover Mission and the People Who Made It Happen (Prometheus), science writer Rod Pyle interviews Rob Manning, chief engineer for the Pathfinder mission and subsequent Mars rovers. Manning recalled that one of the best things about the mission was its relatively minimal requirements. The team was responsible for landing on Mars, delivering the rover, and transmitting images—technically challenging, to be sure, but beyond that the team had no constraints.
Sojourner was succeeded by the rovers Spirit, Opportunity, and Curiosity. Shown here are four mission spares, including Marie Curie [foreground]. JPL-Caltech/NASA
The real mission was to prove to Congress and the American public that NASA could do groundbreaking work more efficiently. Behind the scenes, there was a little bit of accounting magic happening, with the “faster, better, cheaper” missions often being silently underwritten by larger, older projects. For example, the radioisotope heater units that kept
Sojourner’s electronics warm enough to operate were leftover spares from the Galileo mission to Jupiter, so they were “free.”
Not only was the
Pathfinder mission successful but it captured the hearts of Americans and reinvigorated an interest in exploring Mars. In the process, it set the foundation for the future missions that allowed the rovers Spirit, Opportunity, and Curiosity (which, incredibly, is still operating nearly 13 years after it landed) to explore even more of the Red Planet.
How the rovers Sojourner and Marie Curie got their names
To name its first Mars rovers, NASA launched a student contest in March 1994, with the specific guidance of choosing a “heroine.” Entry essays were judged on their quality and creativity, the appropriateness of the name for a rover, and the student’s knowledge of the woman to be honored as well as the mission’s goals. Students from all over the world entered.
Twelve-year-old Valerie Ambroise of Bridgeport, Conn., won for her essay on
Sojourner Truth, while 18-year-old Deepti Rohatgi of Rockville, Md., came in second for hers on Marie Curie. Truth was a Black woman born into slavery at the end of the 18th century. She escaped with her infant daughter and two years later won freedom for her son through legal action. She became a vocal advocate for civil rights, women’s rights, and alcohol temperance. Curie was a Polish-French physicist and chemist famous for her studies of radioactivity, a term she coined. She was the first woman to win a Nobel Prize, as well as the first person to win a second Nobel.
NASA subsequently recognized several other women with named structures. One of the last women to be so honored was
Nancy Grace Roman, the space agency’s first chief of astronomy. In May 2020, NASA announced it would name the Wide Field Infrared Survey Telescope after Roman; the space telescope is set to launch as early as October 2026, although the Trump administration has repeatedly said it wants to cancel the project.
These days, NASA tries to avoid naming its major projects after people. It quietly changed
its naming policy in December 2022 after allegations came to light that James Webb, for whom the James Webb Space Telescope is named, had fired LGBTQ+ employees at NASA and, before that, the State Department. A NASA investigation couldn’t substantiate the allegations, and so the telescope retained Webb’s name. But the bar is now much higher for NASA projects to memorialize anyone, deserving or otherwise. (The agency did allow the hopping lunar robot IM-2 Micro Nova Hopper, built by Intuitive Machines, to be named for computer-software pioneer Grace Hopper.)
And so
Marie Curie and Sojourner will remain part of a rarefied clique. Sojourner, inducted into the Robot Hall of Fame in 2003, will always be the celebrity of the pair. And Marie Curie will always remain on the sidelines. But think about it this way: Marie Curie is now on exhibit at one of the most popular museums in the world, where millions of visitors can see the rover up close. That’s not too shabby a legacy either.
Part of a continuing series looking at historical artifacts that embrace the boundless potential of technology.
An abridged version of this article appears in the June 2025 print issue.
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