The Romans were not the first to associate the bright reddish point in the night sky with the god of war. Long before, the Babylonians named it with a moniker that evoked destruction. Millennia of astronomy and science have only intensified our fascination with the inhospitable red planet.
After observing Mars through telescopes, writing countless stories about its imaginary inhabitants, and visiting it with the first probes, humanity has done something far more extraordinary in recent decades: traversing Mars with robotic vehicles—robotic extensions of our own curiosity that have crossed deserts, scaled mountains, and analyzed rocks, unveiling secrets about how our solar system formed and why Mars transformed from a water-rich world into a frozen wasteland.
What are Mars Rovers?
In simple terms, a Martian rover is a wheeled vehicle designed to move and explore the surface of Mars. Unlike landers and other stationary probes, rovers can autonomously navigate the terrain to study a much broader range of rocks and geological features. Equipped with an array of instruments, they analyze the chemical and physical composition of the soil, rocks, and the thin Martian atmosphere.
The push to send rovers to Mars stems from the desire to uncover the planet’s water history and, by extension, whether it could have harbored life at some point in its past. Rovers search for and characterize rocks and soils that may contain traces of ancient hydrological activity, like minerals that only form in the presence of water.
Early rovers had simpler missions: to demonstrate that the technology worked and to find direct evidence that liquid water had flowed on the Martian surface. The pioneering Sojourner mission demonstrated that wheeled mobility was indeed possible on Mars. Following its success, twin rovers Spirit and Opportunity confirmed the presence of abundant water in Mars’ past, while their successor, Curiosity, sought the essential chemical ingredients to confirm the presence of life.
Finally, the Perseverance rover has been tasked with collecting samples of possible biosignatures for a future mission to retrieve them and bring them back to Earth. While the search for extraterrestrial life often focuses on exoplanets, rovers remain our best asset to confirm past microbial life on other planets in our own solar system.
Design, Instruments, and Processor
Current Martian rovers are about the size of a car and weigh approximately a ton. Their six-wheel design, without springs or shock absorbers, is known as “rocker-bogie.” The “rocker” is the larger arm connected to the chassis, while the “bogie” connects the front and mid-wheels.
This mechanical configuration allows the rover to keep all wheels in contact with the ground most of the time, evenly distributing weight. Thanks to this design, a rover can overcome obstacles up to twice the diameter of its wheels while maintaining incredible stability on steep slopes, adapting to the terrain similarly to an insect.
Though they receive instructions from Earth, rovers are entirely autonomous, the only way to avoid missteps in Mars’ harsh environment. Given the distance between Earth and Mars, a radio signal can take up to 20 minutes to arrive, making real-time control impossible. Instead, engineers send a set of commands for the entire day, and the rover autonomously executes them, using its own sensors to avoid obstacles along the way.
Despite this autonomy, Martian rovers have very limited processors. The central unit, the rover’s “brain,” is responsible for processing images from cameras and controlling wheel motors, as well as operating the robotic arm and managing communications.
Perseverance, the most advanced rover yet, uses a PowerPC 750 CPU, the same chip that powered the iMac G3 in 1998. The choice isn’t due to cost but rather reliability. These processors are highly reliable and “radiation-hardened,” designed to withstand the constant bombardment of high-energy particles from space without failing.
Perseverance is equipped with 23 cameras, some for navigation (Navcams), others for detecting nearby hazards (Hazcams), and the main scientific ones mounted on a mast. They can zoom in, take stunning 3D panoramic images in high definition, and more. Additional instruments include a weather station, ground-penetrating radar to “see” beneath the surface and map rock and ice layers, and microphones to capture sounds of the Martian winds.
Which was the first rover on Mars?
While NASA’s Sojourner is celebrated as the first Martian rover, it was not the first to be sent to the red planet. That often-overlooked honor belongs to the Soviet Union. In 1971, 26 years before Sojourner left its footprints on Mars, the Mars 3 mission carried a small vehicle named PrOP-M.
The design of PrOP-M was unique and never replicated. Rather than wheels, it was designed to glide over the surface using two skis. It was a small 4.5 kg box that had to remain tethered to its lander via a 15-meter cable. Its navigation system was rudimentary yet clever for its time: two small metal bars at the front detected obstacles, triggering an autonomous algorithm to reverse and navigate around them.
The rover’s existence was kept a secret for nearly two decades as it never deployed. On December 2, 1971, the Mars 3 lander accomplished the feat of being the first spacecraft to achieve a soft landing on Mars. However, the triumph was short-lived. After just 110 seconds of operation, during which it transmitted a partial, unrecognizable image, the lander fell silent forever. The most probable cause was a colossal dust storm that swept across the planet at that time, an early warning of how incredibly challenging Martian exploration would be.
How many rovers have been sent to Mars?
To date, six rovers have successfully reached the Martian surface, not including failed attempts: five from NASA and one from the Chinese space agency CNSA. Each rover has had different objectives and contexts, beginning with brief technological tests and culminating in multi-year expeditions.
Sojourner (1997)
The Mars Pathfinder mission opened the pathway for all subsequent missions. Its small rover, Sojourner, comparable in size to a microwave oven, aimed not to conduct groundbreaking science but to demonstrate that it was possible to land and operate a wheeled vehicle on Mars.
To achieve this, NASA employed a risky landing system based on giant airbags that allowed the probe to bounce on the surface and come to a safe stop. On July 4, 1997, Sojourner descended a ramp from the lander (dubbed “Carl Sagan Memorial Station”) and began exploring Ares Vallis.
Intended to operate for only seven sols (Martian days), it exceeded all expectations by functioning for 83 sols. During that time, it traversed just over 100 meters, analyzed rock compositions with its X-ray spectrometer, and transmitted over 550 images back to Earth. Sojourner’s success was not only technical; it became a cultural phenomenon that captivated the global audience, igniting a massive appetite for real-time planetary exploration.
Spirit and Opportunity (2004)
Following Sojourner’s success, NASA raised the stakes with the Mars Exploration Rover mission. Spirit and Opportunity, two identical rovers the size of golf carts, were sent to opposite sides of the planet with the mission to “follow the water.” Powered by solar panels, these robotic twins ultimately rewrote Mars history.
Spirit landed on January 4, 2004, at Gusev Crater, a site that looked like it had been an ancient lake from orbit. However, the surface was covered in volcanic rock. Spirit’s mission transformed in 2007 due to a fortunate accident: one of its front wheels stopped functioning, forcing it to be dragged. In doing so, the broken wheel dug a trench in the ground, revealing bright white material. Analysis showed it to be nearly pure silica—a mineral commonly formed in hot springs or fumaroles on Earth, environments considered ideal for microbial life development. Spirit continued operating until 2010, when it got stuck in fine sand, ending its mission after more than six years of exploration.
Opportunity landed three weeks later, on January 25, 2004, at Meridiani Planum, and had even better luck. It landed inside a small crater, exposing a rock outcrop just a few meters away. Almost immediately, it discovered what it was searching for. The layered rocks and the presence of small iron-rich spheres, nicknamed ” blueberries,” provided irrefutable evidence that this area had once been the shore of a salty, acidic sea. What followed was one of the most extraordinary missions in the history of space exploration. Designed for a 90-day mission and to travel 1 kilometer, Opportunity continued exploring Mars for nearly 15 years, covering a record distance of 45.16 kilometers. Finally, in June 2018, a massive dust storm enveloped the entire planet, covering its solar panels and preventing it from recharging its batteries. After months of attempts to re-establish contact, NASA declared the mission closed.
Curiosity (2012)
With the Mars Science Laboratory (MSL) mission and the arrival of the Curiosity rover on Mars in 2012, exploration of the red planet took a giant leap forward. Curiosity was a complete chemistry and astrobiology laboratory on wheels. About the size of a Mini Cooper and weighing nearly a ton, it was too large for the airbags method. Therefore, NASA designed an incredibly complex landing maneuver called “Skycrane,” where a rocket-powered platform gingerly placed the rover on the surface while rapidly moving away to crash at a safe distance.
Curiosity landed on August 6, 2012, in Gale Crater, chosen for its central 5-kilometer high mountain, Mount Sharp, with sedimentary layers promising to be a record of Mars’ geological history. Unlike its predecessors, Curiosity operates with a Radioisotope Thermoelectric Generator (RTG), providing constant energy and heat to operate its sophisticated suite of ten scientific instruments. Its primary goal wasn’t just to find water, but to determine if Gale Crater ever had the environmental conditions suitable for microbial life.
The answer was a resounding yes. Shortly after landing, Curiosity discovered beds of ancient streams and confirmed that it was in the basin of a freshwater lake containing all the essential elements for life: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. Later, its sample analysis instrument detected complex organic molecules preserved in 3-billion-year-old rocks—the building blocks of life. Today, Curiosity has spent over 12 years climbing Mount Sharp, sending back stunning videos and revealing secrets about how Mars transitioned from a potentially habitable world to the frozen desert we see today.
Perseverance (2021)
Perseverance landed on Mars on February 18, 2021. It is the most advanced rover ever sent to another planet. Based on Curiosity’s successful design, it shares the same chassis and Skycrane landing system but comes equipped with a completely new set of instruments and an even more ambitious mission. It landed in Jezero Crater, a location that once housed a deep lake and river delta, considered one of the best places on Mars to search for signs of past life.
Perseverance’s mission is to search for biosignatures, meaning chemical or mineral traces left by ancient microbial life in rocks. Most crucially, it is collecting samples for future return. Perseverance has a drilling and storage system allowing it to extract rock cores the size of a finger, sealing them hermetically in titanium tubes to leave on the surface for the Mars Sample Return mission—which is currently on standby—to bring them back to Earth for analysis in the world’s most advanced laboratories.
During its time on Mars, Perseverance has made critical discoveries. It has found a broad diversity of organic molecules in the rocks of the crater, reinforcing the idea that life’s basic components were present. It has also collected particularly promising samples. Yet for years, it was overshadowed by a companion: the Ingenuity helicopter, a technology demonstrator that successfully proved it is possible to fly autonomously in the thin Martian atmosphere, lasting 14 times longer than expected.
Zhurong (2021)
On May 14, 2021, the exploration of Mars ceased to be exclusive to NASA. That day, China accomplished an unprecedented technical feat with its Tianwen-1 mission: in its first attempt, it successfully launched an orbiter, landed a platform on the surface, and deployed its first Martian rover, Zhurong. This success made China the second nation to operate a rover on the red planet, marking the beginning of a new multinational era in Mars exploration.
Zhurong, named after the god of fire in Chinese mythology, landed in Utopia Planitia, a vast plain in the northern hemisphere. Unlike NASA’s larger rovers, Zhurong was more comparable in size to Spirit and Opportunity, relying on solar panels for energy. Its main mission was to study local geology, soil composition, and any potential distribution of subsurface water ice.
During its mission, Zhurong traveled nearly 2 kilometers and made significant discoveries. Utilizing its ground-penetrating radar, it determined that it was situated at what had once been the coastline of an ancient vast ocean that covered Mars’ northern hemisphere. The rover also gained fame for its unique feature: a detachable wireless camera that could be left on the ground to take “selfies” next to its landing platform—an ingenious solution that enabled it to beat Perseverance in the race for the best family photo on Mars.
Current Rovers and Their Missions
As of now, only two rovers are fully operational on Mars: Curiosity and Perseverance from NASA.
Curiosity’s current mission is to continue its methodical ascent up the slopes of Mount Sharp, in Gale Crater’s center. As it climbs, it analyzes progressively younger rock layers, which allows it to read Mars’ environmental history over millions of years, understanding in detail how and why the Martian climate changed from being warm and humid—potentially habitable—to the icy, arid desert we see today.
On the other hand, Perseverance is advancing with its dual mission in Jezero Crater. It continues to explore the ancient river delta, utilizing its advanced suite of instruments to search for rocks with the highest astrobiological potential while also collecting and sealing samples of rock and regolith, constructing the first repository of Martian material destined to be brought to Earth by future missions.
From the failed skis of the PrOP-M to today’s nuclear-powered laboratories on wheels, the saga of Mars rovers is one of the greatest technological and scientific epics of our time. Each mission has reshaped our vision of the red planet, transforming it from a distant speck of light into a tangible world with a rich and complex geological history. We have transitioned from asking whether water ever existed to knowing that it flowed in rivers and accumulated in lakes and seas. We’ve shifted from speculating about habitability to finding places that had all the necessary ingredients for life.
The Ingenuity helicopter accompanying Perseverance has opened the door to a new concept of flying robots, which will reach another level when NASA sends the Dragonfly mission to Titan, Saturn’s moon covered in methane seas—one of the most fascinating places in the solar system.
As for Mars, it will continue to receive visitors for the sample return mission, a milestone where China’s Tianwen-3 mission competes with the United States’ Mars Sample Return. The definitive answer to the question of whether life ever existed on Mars will likely be obtained here on Earth, where we can analyze those Martian rock samples with the full power of terrestrial laboratories.
Images | CNSA, NASA