From Sojourner to Perseverance: How Rovers Shape the Future and Our Love for Cute Things
From the first rover that landed on Mars 27 years ago, Sojourner, to car-sized Curiosity and Perseverance – we’ve seen quite an evolution in how these rovers improved. Not only have they got more technologic
ally advanced, they also unleashed a culture of cuteness that we associate with rovers.
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| Pathfinder photographs Sojourner as it analyzes the rock Yogi; Source: Wikipedia |
On December 4, 1996, a Delta II rocket took off from Cape Canaveral, carrying one of the most meaningful missions of its time: the Mars Pathfinder. About half a year after launch, Pathfinder touched down on the Red Planet.
After the successful landing, Pathfinder made way for a tiny but revolutionary companion: Sojourner. Being the first rover to explore Mars, the microwave-sized Sojourner became quite a celebrity. And Sojourner was the beginning of a new era of space exploration — ever since, rovers became bigger and technologically more complex.
But how did these rovers shape our understanding and fascination with the Red Planet? And what does the future hold for robotic exploration?
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| Panoramic view from the Pathfinder lander; Source: Wikipedia |
Before the Space Age, humanity always looked at Mars with wonder; through telescopes, it looked like a dynamic planet, with dark albedo features and polar ice caps, and many thought it’s a world as teeming with life as Earth.
So scientists and engineers targeted the Red Planet as soon as the first s
pacecraft were built – and what they revealed was a planet as dead as the Moon.
That discovery came as a big disappointment to those who thought that Mars is a world of hospitality. But apparently, it was all just misbelief.
Today we know that even though the Red Planet looks dead, it’s much more complicated and was once a habitable haven with oceans and a thick atmosphere. However, we couldn’t have learned much of that without the aid of rovers.
When scientists first sent Sojourner to Mars they didn’t have big expectations for the small rover – it had a planned lifetime of merely seven sols (Martian days). All that scientists wanted to know was whether it was possible to operate a rover on Mars. However, Sojourner proved that it was much sturdier than expected; the rover operated for 83 sols!
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| Pathfinder photo of Ares Vallis, with the Twin Peaks hills in the background; Source: Wikipedia |
The solar-powered rover differed much from the modern, nuclear-powered rovers Curiosity and Perseverance (aka Percy). Sojourner had travelled just 100 meters (330ft) during those 83 sols, roving around Ares Vallis in the Oxia Palus quadrangle.
Both Pathfinder and Sojourner took a lot of images of Ares Vallis, and although cameras on rovers have since improved significantly, those photos shaped our perception and modern fascination with the Red Planet — maybe we haven’t walked on its surface yet, but it somehow looks like home.
Sojourner also revealed a lot about the Martian geology, thanks to the Alpha Proton X-Ray Spectrometer (APXS), which aided the rover in analyzing rocks around its landing site. Those rocks became really famous. A big boulder near the landing site was named Yogi, another one got the name Pop Tart.
Sojourner roved just a small area, but that region would shape future missions to Mars, all defined by a robotic duo of lander and rover.
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| Artist's concept of one of the MER exploring a rock on Mars; Source: Wikipedia |
The first rover already unveiled Mars’ hidden past of habitability, but it would be the next pair of rovers that discovered even more about its geology: the Mars Exploration Rovers (MER) Spirit and Opportunity.
Compared to Sojourner, the MER were a major upgrade. Not only were they bigger, they also started to evolve to the design that we see in the Curiosity and Percy rovers – and they kind of resembled WALL-E.
Spirit was launched a month before Opportunity on June 10, 2003 on top a Delta II and landed on January 4, 2004 in the Gusev Crater in the Aeolis quadrangle. Its sister, Opportunity, which received the nickname Oppy, lifted off in a Delta II Heavy and landed on the Meridiani Planum, one of the best explored places on Mars.
The expected life span for each rover was 90 sols, a big leap from the seven sols for Sojourner. And Spirit and Oppy not only exceeded that limit, they literally thrived for years to come.
Just like Sojourner, the rovers were solar-powered, but they carried a variety more of scientific instruments. Among these are tools to study rocks up close, such as a rock abrasion tool and a magnet array, as well as a robotic arm to take close-up images of targets. The rovers also had more sophisticated cameras, allowing for stunning panoramic photos in full color.
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| The Mars moons Phobos and Deimos as seen by Spirit. The moons orbit Mars very quickly; the bigger moon Phobos rises twice per sol! Source: Wikimedia Commons |
Spirit travelled a total of 7.7km (4.8 miles) before it got stuck in sand in late 2009. Oppy, which operated well into 2018, made it even further: 45km (28 miles).
They left a legacy of scientific discovery. Spirit and Oppy both found traces of ancient lakes, with rocks altered by water and evidence for flows of water. Oppy also became the rover to find the first meteorite on an extraterrestrial surface; the Heat Shield Rock, roughly the size of a basketball.
The rovers taught engineers on Earth important lessons for future rover designs to avoid mechanical failures and rovers falling victim to rough weather.
The MER truly showed how much affection humans can have to robots; Spirit was featured in a comic, and the movie “Good Night Oppy” depicts the rover’s miraculous journey. When news of Oppy’s mission end came in 2019 following a global dust storm after which the rover stopped responding, everyone declared Oppy as “dead.”
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| Oppy's last image... Source: Wikipedia |
Solar-powered systems worked well for Sojourner, Spirit, and Oppy, but a global dust storm can easily wipe these rovers out of service. Despite so-called cleaning events, where wind swipes the sand off the solar panels, it became clear that for a robot to rove for a long time on the Red Planet, solar pabels don’t work that well.
Solar panels also diminish the amount of time scientists can study Mars when a rover has to hibernate. A solution for this came with Curiosity, the next rover in line to land on the Red Planet. It touched down in Gale crater in the Aeolis quadrangle on August 6, 2012 after the infamous “Seven Minutes of Terror” landing and has since investigated the area.
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| Self portrait of Curiosity; Source: Space |
If you’ve seen the self portraits Curiosity took, you may also have thought “cute!” But don’t be fooled – Curiosity is the size of a car, powered by nuclear batteries. These nuclear batteries work thanks to the decay of radioactive isotopes like plutonium.
Another factor that makes Curiosity stand out from the previous rovers is one specific goal — to provide enough information for future crewed missions to Mars.
Thanks to Curiosity’s improved photo capabilities, the rover has already produced more than 600’000 raw images available to the public. And, in the 12 years since it landed on Mars, it’s close to breaking Oppy’s record as the longest-operating rover.
One of Curiosity’s prime objectives is identifying whether Mars could have ever had life. Not only does the rover measure radiation levels with the Radiation Assessment Detector (RAD) and Dynamic Albedo of Neutrons (DAN), it also drills holes in the ground to analyze the composition of Martian rocks.
An exciting discovery that came from the first drill samples are the building blocks of life – carbon, oxygen, nitrogen, hydrogen, sulfur, and phosphorus. It doesn’t mean that there’s life on the Red Planet, but it’s the first step in determining whether life was once thriving here.
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| Curiosity's view of a sunset on Mars, with Sun going down to the right of Mount Sharp; Source: Wikipedia |
Ginny clearly showed that flying on the Red Planet is a valuable choice for future scientific missions. The helicopter exceeded its planned altitude and reached a ceiling of 24 meters (79ft)! It also exceeded the planned amount of five flights, finishing 72 flights. This January, one of Ginny’s rotor blades broke, and Percy had to abandon the helicopter to continue its mission.
While a lot of Percy’s technology is similar to Curiosity’s, the rover collects rock samples that a future sample-return mission will bring to scientists on Earth for study.
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| Percy's view of the rim of Jezero crater; Source: Wikipedia |
One interesting instrument is the Mars Oxygen ISRU Experiment (MOXIE), which attempts to produce oxygen from carbon dioxide in Mars’ atmosphere. MOXIE successfully produced five grams of oxygen in April 2021 – this could be useful for future crewed missions or to produce fuel for return missions.
In the three Earth years that Percy has already spent on the Red Planet, it travelled 25km (15 miles), coming close to the 31km (19 miles) Curiosity has already roved.
Just a few months after Percy arrived in Jezero crater, Mars got another robotic visitor: Zhurong. Zhurong is part of the China National Space Administration’s (CNSA) Tianwen-1 mission to Utopia Planitia, the country’s first rover.
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| Self portrait of Zhurong with lander; Source: Wikipedia |
Visually, Zhurong resembles Spirit and Opportunity — it’s also powered by solar energy, planned to operate for 90 sols. Zhurong exceeded that and lived for half a Martian year, breaking down during the Martian winter amidst dust storms. Sadly, no cleaning event allowed Zhurong to operate any further and the mission’s end was announced in 2023.
Zhurong found that Mars’ climate changed dramatically about 400’000 years ago, during the Red Planet’s last major ice age.
At the moment, there are two active rovers on Mars: Curiosity and Percy. However, they are obviously not the last ones, with more to follow. NASA’s focus for now will be on a return mission to collect the samples Percy took.
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| One of the many prototypes for Rosalind Franklin, here being tested in the Atacama desert in 2013; Source: Wikipedia |
Meanwhile, the ESA is working on the Rosalind Franklin rover, named after the British chemist and DNA pioneer. It was supposed to launch in July 2020, then delayed to 2022. The Russian space agency, Roscosmos, was also involved in the mission, but the ESA ended cooperation with Roscosmos after Russia’s invasion of Ukraine. Because of that, Rosalind Franklin won’t be launched before 2028 in order to build a new lander.
Other focus lies on orbiters and landers. In 2026, JAXA plans to launch the Martian Moons eXploration (MMX) mission for sample returns from Phobos. JAXA is also working on a rover concept named Mars Exploration of Life and Organism Search (MELOS). MELOS also potentially comes with an aircraft!
Rovers of the future will become even more interesting. We are used to the six-wheeled rovers, but NASA is currently testing robodogs for lunar exploration. These robodogs can navigate through rough terrain and are more adaptable to terrain. Who knows, maybe one day these robodogs also venture on the Red Planet!
Robotic exploration of Mars is taking a turn — rovers are still important, but they will become more diverse as time passes. Whether they be robodogs or even fixed-wing aircraft, robots will revolutionize extraterrestrial exploration.
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