On July 4, 1997, a tiny, flat robot touched down on the surface of Mars and became the first wheeled vehicle to roam around on another planet. Since then, a fleet of Martian rovers have followed in the tracks of Sojourner and they have become bigger, better, and more autonomous over the years.
Sojourner was followed by Spirit and Opportunity, both landing on Mars in 2004. Curiosity, which is still roaming the dusty Martian terrain, landed in 2012, and finally, the latest addition to the rover fam, Perseverance touched down in 2021.
Although the legacy of NASA’s Mars rovers are well known, these other-worldly explorers are a world of hidden gems on their own. Here are lesser known facts sprinkled across nearly three decades of Martian robot history that you may not have known about before.
Secret code
As Perseverance descended towards Mars’ Jezero Crater on February 18, 2021, its parachute had two messages encrypted in binary code. The inner portion of the parachute spelled out “DARE MIGHTY THINGS,” with each word of the Jet Propulsion Laboratory motto located on its own ring of gores (individual segments that make up a parachute) while the outer band had the GPS coordinates for NASA’s JPL in Southern California, where the rover was built.
Traveling backwards
On March 13, 2006, the Spirit rover’s front wheel broke, likely due to a broken circuit in the motor that powered the wheel. After engineers lost hope that the robot’s wheel could keep turning, they began driving Spirit backwards while dragging the inoperable right-front wheel behind.
That unfortunate malfunction led to a surprising discovery by Spirit. In 2007, the rover’s broken wheel kicked up bright white soil, which turned out to be concentrated silica deposits. “It showed that there were once hot springs or steam vents at the Spirit site, which could have provided favorable conditions for microbial life,” Steve Squyres, principal investigator for Spirit and Opportunity, said in a 2011 statement.
Slow and steady
The Mars rovers are way slower than you think.
Curiosity and Perseverance both move at roughly the same clip, at around 0.1 miles per hour (4.2 centimeters per second, or 152 meters per hour). “For comparison, a 3 mph walking pace is 134 centimeters per second, or 4,828 meters per hour,” NASA says. The rovers were designed to trek up to 100 meters (about 110 yards or 328 feet) across the Martian surface on each Martian day.
But when it comes to the total distance traversed, the rovers are achingly slow. Considering that there’s a time lag between Earth and Mars, engineers send commands to the rovers and wait to examine the data that they send back before moving the rovers along their trek. It takes around 20 minutes for a radio signal to travel the distance between the two planets, depending on their positions.
Lucky coin
Curiosity has had quite the lucky streak on Mars, perhaps due in part to the rover’s secret weapon. The Curiosity rover is carrying a 1909 VDB penny minted in Philadelphia during the first year that Lincoln cents became available. The lucky penny actually has a practical use as a calibration target for the robot’s Mars Hand Lens Imager (MAHLI) instrument.
Say my name
Perseverance is the rover of the people, carrying the names of 11 million Earthlings on its back. Before its launch, NASA invited the public to submit names to be sent on the journey to the Red Planet. Engineers stenciled the 11 million names onto the finger-nail sized chips using an electron beam, which were then mounted to a small plate attached to the center of Perseverance’s aft crossbeam.
Morse code tracks
Wherever Curiosity goes on Mars, it leaves behind a special message disguised in its trail. The straight lines in Curiosity’s zigzag track marks are Morse code for “JPL,” the acronym for NASA’s Jet Propulsion Laboratory—the rover’s birthplace. The specific Morse code is: .—- (J), .—. (P), and .-.. (L).
Mars memorial
NASA’s Spirit and Opportunity rovers, by carrying small pieces of the wreckage, paid tribute to the victims of the September 11, 2001, attack on the twin towers of the World Trade Center. Aluminum recovered from the destroyed World Trade Center towers was fashioned into an aluminum cuff serving as a cable shield on each of the rock abrasion tools on the rovers.
Opportunity’s “last words”
On June 10, 2018, when news broke out that Opportunity’s mission had ended on Mars, science reporter Jacob Margolis jokingly tweeted that the robot’s last words were, “My battery is low and it’s getting dark.” The famous last words spread like wildfire, with some attributing the literal phrase to the robot. Opportunity obviously didn’t say that—it communicates in data and is completely devoid of sentience. The misquote became so widely circulated and misinterpreted that Margolis had to write an article clarifying that the last words were a poetic interpretation of the robot’s final moments.
Comet spotter
NASA’s Opportunity rover snapped the first-ever image of a comet from the surface of Mars. On October 19, 2014, Comet C/2013 A1 Siding Spring passed much closer to Mars than any previous known comet flyby of Earth or Mars, missing the Red Planet by a mere 87,000 miles (139,500 kilometres). Opportunity was there to witness this moment in celestial history, snapping a fuzzy image of the Oort cloud comet as it made its way across the pre-dawn Martian sky.