The Curiosity rover celebrated a milestone birthday this month – an impressive nine years of exploration on Mars, and still going strong. The day a rover lands on Mars is typically considered its birthday – with Curiosity being ‘born’ on August 6th 2012. At that time, Curiosity was the most advanced, complex and largest rover ever built for exploration on another world. Despite being designed for a primary mission of just two years duration, Curiosity has far outlived its original lifespan and made countless discoveries along the way. So, what has Curiosity found after all these years, and how much longer might it survive on Mars?

Next generation of advanced rovers

Curiosity has proved a highly successful rover mission, but it is far from the first to explore the red planet. Sojourner was a true pioneer when the microwave-sized rover explored Mars for several months in 1998. NASA followed this success with the twin rovers Spirit and Opportunity. Both landed in 2004 and dramatically increased what we knew about Mars. The twins were like robot geologists and were able to give insight into the changing conditions on Mars and what it was like in the past. Discoveries made by these rovers hinted for the first time that Mars was once a water world much like Earth, but they lacked the scientific instruments that could confirm this theory.

This is where Curiosity came in. NASA designed this rover to detect signs of water and if investigate if conditions were ever right for microbial life to develop. The rover is much larger than its predecessors, weighing almost 900 kilograms (compared to the Spirit and Opportunity twins weighing in at just 185kg). Curiosity is almost twice as large too, much more comparable to the size of a car, where as the twin rovers were comparable to a golfcart. Curiosity also contained a far more complex suite of cameras, instruments and drills to investigate the conditions on Mars. Curiosity was not just an updated version of the twin rovers; it was a completely new type of rover. Many of the systems aboard the rover simply did not exist when Spirit and Opportunity were conceived, and NASA even had to develop a more complex landing system to ensure they could safely land such a heavy rover on Mars.

The landing site was an important decision for NASA too. Not all of Mars was thought to contain water, so they had to pick somewhere where conditions would have been favourable for water to form in the past. Eventually the 154km wide Gale Crater was selected as Curiosity’s landing site. The large crater displayed tell-tale signs of past water from orbiting spacecraft, and it was theorised that the crater was in fact a dried lakebed.

A simulated view of the ancient lake that existed in Gale Crater some 3.5 billion years ago.

Curiosity was launched from Cape Canaveral in late 2011, and after a nine-month journey to Mars it successfully landed in Gale Crater on August the 6th 2012. It was a nerve-wracking process as many of the systems developed to land the large rover had never been used, but Curiosity landed flawlessly and in the process made history as the largest and heaviest object ever landed on another planet.

The first image snapped by Curiosity after it successfully landed in Gale Crater. NASA/JPL

What has Curiosity found so far?

After its successful landing, Curiosity got straight to work and within months started making huge discoveries. The mission team began to assess which path Curiosity would take as it drove towards and eventually up the slopes of Mount Sharp – officially known as Aeolis Mons – a 5.5km high mountain which forms the central peak within the Gale Crater. In September 2012, Curiosity found evidence of an ancient streambed that suggest there was once large amounts of flowing water in the area. Just a month after this, the rover performed a chemical analysis of soil that revealed the presence of water molecules sulphur and chlorine in the Martian soil. This was a huge discovery for Curiosity, and the mission team pushed on as the rover began to drive towards other locations of interest. In March 2013, NASA reported that Curiosity has confirmed that geochemical conditions in Gale Crater were once suitable for microbial life after analysing rock samples. This was another huge achievement for Curiosity and a fulfilment of one of its mission goals. On Curiosity’s first birthday, NASA programmed the rover to sing ‘Happy Birthday’ to itself – a somewhat lonely birthday party for the rover at the end of an extremely successful first year on Mars.

2014 was another big year for Curiosity, as the mission team announced that the rover’s primary goal would now be to search for direct evidence of life. In late 2014, NASA announced that Curiosity has detected a tenfold spike in the amount of methane in the Martian atmosphere. The measurements taken over a 20-month period showed that the readings were seasonal. This was a huge discovery, as methane is a sign of organic life on Earth. The chemical had not been detected in the atmosphere by orbiters, so the discovery on the ground was a revelation. Methane can be produced by naturally accruing geological processes, but this would not account for why the rise in methane would be seasonal. The discovery to this day stands as one of the most significant that the rover has made – but the origin of these methane spikes has not yet been entirely explained and remains a mystery.

Curiosity’s view of a large outcrop of mudstone at the bottom of Mount Sharp. NASA/JPL

As Curiosity celebrated its 5th birthday in 2017 it was providing insight into the radiation levels that humans would experience on the surface of Mars. The mission team announced that a solar storm had caused the radiation levels to double on the surface, causing an aurora 25-times brighter than any ever observed on Mars previously. Curiosity’s drill began to break around this time, and damage to the rovers’ wheels became more evident as it continued to traverse up steep, fractured terrain. The rover also began to experience problems with its onboard computer, and NASA had to switch systems several times to ensure it could continue to operate.

Curiosity snaps a selfie on Mars after drilling a hole into the ground. NASA/JPL

In 2018, Mars experienced a global dust storm that engulfed the entire planet in a haze of thin dust particles. The storm hit Gale Crater in June, blanketing the area in darkness for several months. The Curiosity rover was designed to withstand such events however, drawing its power source from plutonium, not solar power. Curiosity rode out the storm and continued on generally unaffected by the storm, but its predecessor did not fare as well. The older Opportunity rover was still active on Mars at the same time, but this rover did run on solar power. Opportunity was eventually killed by the storm, as dust blocked out the Sun and caused the rover to fall silent as it ran out of battery. It brought an end to an incredible 14 years of exploration on Mars – a record which Opportunity still holds to this day. The end of Opportunity’s mission made Curiosity the lone active rover on Mars, but not for long. The continued success of Curiosity led NASA to develop Perseverance, a highly advanced rover whose design was based heavily on Curiosity but carrying far more advanced tools. Perseverance’s mission would be to search for ancient and potentially fossilized life on Mars, based on the groundwork done by Curiosity confirming favourable conditions.

Curiosity was imaged by the orbiting MRO spacecraft as it continued to climb the slopes of Mount Sharp. NASA/JPL

As of August of 2021, Curiosity has driven 26 kilometres across the surface of Mars, an impressive distance, but not to be outdone by Opportunity who maintains the record of travelling 45 kilometres during its lifespan. Curiosity has now far outlived its expected lifespan, but continues to make discoveries on Mars. You can track the progress of Curiosity in real-time here: Where is Curiosity? | Mission – NASA’s Mars Exploration Program

How long will it last?

Just like the tragic end of Opportunity in 2018 due to a dust storm, Curiosity will not last forever and its days on Mars will eventually come to an end. The rover has experienced increasingly major computer and memory issues since 2016. The rover carries two computers or ‘brains’ that the mission team can alternate if one of them experiences a problem. Radiation levels on Mars are high and typical electronics would be fried if exposed to the harsh conditions. Curiosity does carry hardened and radiation-treated computers, but they still experience problems that would not be occur on Earth, and eventually the computers will degrade due to the harsh radiation. The mission team has had to rely on one side of the rover’s brain, as problems on the second side continue to cause issues which prevent the rover from storing key data. Since 2018, the issue has not been remedied and the rover continues to operate on just one computer – meaning that there is now no back up. If Curiosity’s computer were to experience a serious issue, this would likely spell the end for the rover.

Curiosity captured this image of a rock formation known as Mont Mercou, along with thin clouds of water ice in the Martian sky. NASA/JPL

In recent years Curiosity’s wheels have also experienced serious wear-and-tear as it traverses the red planet. Large punctures and holes have been imaged by the rover, showing that the wheels are slowly breaking down under the harsh and cold conditions. The rocks on Mars were found to be much more jagged and brittle that previously thought, and they have pierced through the rover’s wheels with ease over time. These holes were first detected in 2014, and as of 2021 the wheels are displaying increasingly heavy damage. The mission team has altered the way the rover moves to try and minimise the damage to its wheels, and later designs for Perseverance’s wheels were modified to be much more durable and stronger than Curioisty’s. If the rover were to breakdown and become immobile on Mars, this would not necessarily end the rover’s mission. It could act as a ‘stationary science platform’ and continue to study the area around it, but it would severely reduce its capabilities if it were unable to move across the Martian surface. The rover is safe from other dangers like dust storms since it does not require solar power, but it’s plutonium battery will eventually run out of energy. This power source will keep Curiosity alive for a bare minimum of 14 years, but this is likely to be much longer as different instruments can be turned off to conserve power.

Curiosity has sustained a lot of damaged to its wheels over the past 9 years on Mars, evident in these images. NASA/JPL

If Curiosity can survive until 2026, it will become the most long-lived and durable rover on Mars, surpassing Opportunity’s record. It is a long way off, but the rover has already shattered its previous lifespan estimates as it continues to surprise us with its continuous discoveries. Regardless of when Curiosity will eventually fall silent on Mars, its legacy and impact will live on. It will stand on Mars as a true pioneer of exploration, having forever changed our understanding of how Mars formed and searching for signs of life.

Maybe one day in the future, human explorers will visit the silent Curiosity on the surface of Mars as we continue on our path of discovery and exploration made possible by our robotic pioneers.

A beautiful view of the slopes of Mount Sharp by Curiosity. NASA/JPL