It took Opportunity nearly 15 years to build the record for driving on another world. Perseverance has beaten it in five and a half.
NASA's Perseverance rover reached 28.10 miles (45.22 kilometers) on its odometer on October 11. Opportunity, which explored Mars from 2004 to 2018, finished with 28.06 miles (45.16 kilometers). Perseverance moved ahead on its 2,006th Martian day, or sol, and no vehicle has now driven farther across the surface of another world.
Perseverance is ahead by only about 0.04 miles, but it got there much faster than Opportunity did. The method behind the drive matters more than the final figure.
A rover that does most of its own driving
Perseverance uses an autonomous driving system called AutoNav. Commands from Earth arrive after a long communications delay, and AutoNav lets the rover cross much of the Martian ground without waiting for step-by-step driving instructions.
As it drives, the rover keeps photographing the area around it, builds a three-dimensional map of possible obstacles and chooses a safe path between the destinations mission controllers set. NASA engineers have a name for this: “thinking while driving.”
All of this happens at or close to the rover’s top speed, which means Perseverance can travel up to 1,351 feet (412 meters) in one sol. AutoNav has evaluated the terrain for over 90% of the total distance the rover has covered.
Earlier rovers relied on it far less. Autonomous navigation on Opportunity and its twin, Spirit, handled only about 5% of their driving distances. Sojourner, NASA’s first Mars rover, worked out its safest route from just 20 measurement points. Perseverance looks at approximately 600,000 points each time it checks the ground ahead.
Steven Lee, the project manager of the Curiosity and Perseverance rovers at NASA’s Jet Propulsion Laboratory in Southern California, said: “It is an honor to be working on Perseverance at a moment when the technology has evolved to the point that drives like these are routine. The original mission called for no more than 12.4 miles of driving. We’ve blown well past that, and with all mobility systems fully operational and favorable extended-ground-life test results, we expect Perseverance to keep adding to this record for many years to come.”
NASA has already approved the rover’s first mission extension. It began in October and keeps Perseverance working along the rim of Jezero Crater until approximately the end of 2028.
Glare from the Sun is the next hurdle
The team admits the software has limits. Strong sunlight creates glare in the navigation cameras, and that makes the ground harder for the software to interpret. If Perseverance is heading toward the Sun, planners currently halt it by mid-afternoon.
Mark Maimone, deputy team chief for robotic operations on Perseverance, put it this way: “The rover that broke this record did so by making its own decisions about the path. Given the autonomy to just go, Perseverance is a better driver than the one that landed, and we’re not done. Our newest software teaches Perseverance to steer less and roll more, and to check its own position against orbital maps mid-drive. The next frontier is sunlight itself. Glare in the navigation cameras is why we park by mid-afternoon if we’re driving toward the Sun, and if we can teach the rover to see past those artifacts, every rover that follows gets a longer working day.”
A fix would give Perseverance, and the Mars rovers that come after it, more of each day for exploration.
The ground where it happened
Perseverance passed Opportunity’s total on its way to a site called “Idubi,” while crossing an area beyond the western rim of Jezero Crater called “Lac de Charmes.” The terrain there may rank among the oldest ever studied in the solar system.
Rocks like these have mostly disappeared on Earth, worn away by erosion or recycled by plate tectonics, which keeps renewing the planet’s crust. Mars has no tectonic plates, so its ancient rocks survived. Scientists hope Idubi will show evidence of ancient hydrothermal systems, where heated water once flowed through rock and may have produced conditions suitable for life.
Some of the rim rocks date to major impacts approximately 4 billion years ago. They preserve a record of a very early stretch of planetary history that Earth’s geology has mostly wiped out.
Distance is a tool for science
Setting distance records isn’t why NASA sends rovers to Mars. Covering more ground, and covering it faster, lets scientists reach more geological formations, sample a broader range of rocks and piece together the planet’s environmental history.
Perseverance began on an ancient lakebed inside Jezero Crater and then drove through the remains of a river system that once carried water and sediment into the basin. On that route it found a rock called “Cheyava Falls,” where scientists identified a potential biosignature: a feature or chemical pattern that could indicate past life, although nonbiological processes can sometimes leave similar signs.
On the crater rim, researchers are asking something different. They want to know whether hydrothermal activity took place there. These systems form when water comes into contact with hot rock, and they can produce chemical conditions that might support microbial life.
So far the rover has gathered 29 samples of rock and regolith, the loose material that covers the Martian surface. The samples come from the crater floor, the crater rim and a fan-shaped deposit left behind by an ancient river.
When the work at Lac de Charmes wraps up, Perseverance is expected to continue along the rim and later turn south during the extended mission. Rainbow Falls is one of the planned stops. It is a section of ancient Martian crust 328 feet (100 meters) wide that was thrust upward by the impact that formed Jezero Crater.
Almost three decades of rovers on Mars
The new record comes nearly 30 years after the first Mars rover touched down. Sojourner landed in 1997. About as big as a microwave oven, it traveled approximately 330 feet (100 meters) over its 83-sol mission.
Spirit and Opportunity landed in 2004. Each was about the size of a golf cart and designed to last only 90 Martian days, and both outlived that by a wide margin. Spirit drove 4.8 miles (7.7 kilometers) before its mission ended in 2010, when it did not survive the Martian winter.
Opportunity lasted 5,111 sols. In 2015 it became the first vehicle to complete a marathon distance on another world, and its final tally held the record until this month.
Curiosity landed in Gale Crater in 2012, is still operating and has covered more than 23.65 miles (38.07 kilometers).
Perseverance had already overtaken the Moon’s best totals earlier in its mission. In 1972, Apollo 17 astronauts Gene Cernan and Harrison Schmitt drove 22.2 miles (35.7 kilometers) on the lunar surface. The following year, the Soviet Union’s robotic Lunokhod 2 rover traveled 24.2 miles (39 kilometers). Perseverance has gone past both, and its original mission plan called for no more than 12.4 miles of driving in total.