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Mars Rovers and the Search for Answers

Six Wheels Built for Rough Ground

NASA's Mars rovers use six wheels instead of four because a rocker-bogie suspension system lets each wheel move independently over boulders, sand, and steep slopes without the whole vehicle tipping over. This design, first tested on the Sojourner rover in 1997, has proven durable enough that later rovers like Curiosity and Perseverance climb obstacles nearly a wheel's height tall while keeping their body and instruments level and stable.

Because a round trip radio signal between Earth and Mars can take anywhere from about 6 to 44 minutes depending on the planets' positions, a rover cannot be driven with a joystick in real time. Instead, engineers on Earth plan a day's route in advance, and the rover's onboard computer uses cameras and hazard-avoidance software to navigate that path safely on its own.

The Mast, Cameras, and Robotic Arm

The tall mast on a rover carries navigation cameras that act like eyes, letting the science team back on Earth build 3D maps of the Martian terrain and plan safe routes around large rocks or soft sand traps. Some masts also hold a laser instrument that can vaporize a pinhead-sized speck of rock from several feet away just to analyze what gas and dust the flash releases.

The robotic arm folds and extends to bring tools directly to interesting rocks, including a drill that can bore into stone to collect a powder sample, and a magnifying camera that photographs mineral grains up close. Perseverance, which landed in 2021, even carries sample tubes and seals them for a future mission that hopes to bring pieces of Mars back to Earth for the first time.

A Red, Rocky, and Dusty World

Mars gets its reddish color from iron oxide, essentially rust, coating dust and rock across its surface, and that same fine dust regularly kicks up into planet-wide storms that can last for weeks and block sunlight from reaching solar panels. Mars is also home to Olympus Mons, the tallest known volcano in the solar system, standing about three times the height of Mount Everest, along with Valles Marineris, a canyon system long enough to stretch across the entire continental United States.

Surface temperatures on Mars swing wildly, from around 70 degrees Fahrenheit at the equator during the day to well below minus 100 degrees Fahrenheit at night, since the planet's thin atmosphere holds almost no heat once the sun sets. That thin atmosphere, only about 1 percent as thick as Earth's, is also why a parachute alone cannot slow a spacecraft enough to land safely - rovers rely on a mix of parachutes, retrorockets, and in Curiosity and Perseverance's case, a hovering "sky crane" that lowers the rover on cables before flying off to crash a safe distance away.

Working Long Past Their Planned Mission

The rover Opportunity was designed for a 90-day mission when it landed in 2004, yet it kept exploring the Martian surface for almost 15 years before a massive dust storm finally ended communication in 2018, traveling more than 28 miles in total - a distance record for any vehicle on another world. Its twin rover Spirit worked for six years before getting stuck in soft sand, and both rovers together sent back tens of thousands of images that reshaped scientific understanding of ancient water on Mars.

Today's rovers search specifically for signs that Mars once had the right conditions to support microbial life, since evidence already shows the planet had rivers, lakes, and even an ocean billions of years ago. Every rock a rover like the one in this scene stops to examine is a small piece of evidence in that much larger ongoing investigation.