Last updated May 2, 2018 at 12:35 pm
It’s the Mars rover that just won’t quit – Opportunity has clocked up 5,000 Martian days exploring the red planet. And it’s still serving up surprises.
On Saturday 17 February, the NASA-operated rover Opportunity awoke to its 5000th sol, or Martian day, on Mars.
But rather than celebrating, the dependable rover just kept plugging away on its scientific mission.
Each sol, a Martian day, is slightly longer than Earth’s at around 24 hours and 40 minutes, meaning Opportunity has been working for 5,137 Earth days, or just over 14 years. High school students have been born since Opportunity started operating.
This remarkable longevity has been a surprise for everyone involved in the mission – originally it was only designed for a mission lasting 90 sols. When launched, it’s doubtful anyone expected it to operate at least 55-times longer than planned.
Opportunity landed on Mars on 25 January 2004, three weeks after its twin rover Spirit, and has been roving and studying the red planet ever since. NASA lost contact with Spirit in 2010, but Opportunity is still going strong and doing extraordinary science.
Longer, stronger, further
The six-wheeled rover is rather diminutive – standing 1.5 metres tall, 2.3 metres wide and only 1.5 metres long. Weighing 180 kilograms, it’s around one fifth the weight of the more modern, and larger, Curiosity rover launched in 2011.
One of the secrets to its longevity is its solar arrays, which can collect power for up to fourteen hours every sol, while rechargeable lithium ion batteries store energy for use at night. Opportunity has also weathered fierce dust storms, including global storms in 2007 during which it could only operate for as short as a few minutes per day.
Over the past 14 Earth-years, Opportunity has set the record for the longest distance driven on another planet, having travelled 45 km since it landed. While that might not sound like much, because it can take up to 24 minutes for control signals from Earth to reach Mars, Opportunity creeps along with a top speed of only 0.18 km/h. Any faster and there is the risk it could get itself into trouble before its controllers on Earth can react.
Despite this slow journey, Opportunity’s route may well be the best documented 45 km in the whole solar system, with the rover having sent back more than 225,000 images during its mission. That’s an average of 5 images every metre it has travelled.
Basically – a ‘millennial taking selfies on a night out’ level of photography.
Opportunity revolutionised our knowledge of Martian geology
Between the massive library of photographs and its onboard scientific equipment, having lasted so long and travelled so far Opportunity has been able to study Martian geology in incredible detail. During its elongated mission, it has revolutionised our understanding of the nature of the planet.
The primary goal of Spirit and Opportunity’s mission was to study Martian rocks and soils for evidence of past water activity on Mars. Opportunity discovered sediments and mineral formations that indicate its landing site was once a salty pond or sea.
After travelling to the site of impact of its own heat shields, Opportunity also discovered “Heat shield rock,” the first ever meteorite discovered on Mars.
Now, with its primary mission completed, Opportunity is searching for signs of ancient life, or any evidence that Mars could have been habitable in the distant past.
As well as geology, Opportunity has also been studying Mars’s climate and atmosphere. By combining data obtained by Opportunity on the ground with data obtained by the Mars Global Surveyor satellite in orbit, NASA scientists have been able to build up a more complete picture of the Martian atmosphere than either mission could alone.
Opportunity has also been performing astronomical observations, photographing Earth from the Martian surface, and watching Mars’s moons Phobos and Deimos as they passed in front of the Sun.
New discovery may point to water and snow
Not one to rest on its laurels, Opportunity’s discoveries keep coming, Recently, in the sloping walls of Endeavour crater, the aging rover found rock stripes.
On Earth, rock stripes are formed on the sides of mountains when the repeated freezing and thawing of wet soil causes small stones in the soil to be distributed into distinctive lines. If Opportunity is seeing evidence of this process in Endeavour crater, it could mean ice and snow were forming and thawing on the walls of the crater in the relatively recent geological past, a finding that would reshape our understanding of the geology and climate of Mars over the eons.
However, the rock stripes could have been formed by other means, such as wind, or by a combination of processes. More study and evidence is needed to pin down the cause of the surprising formations.
“Perseverance Valley is a special place, like having a new mission again after all these years,” said Opportunity Deputy Principal Investigator Ray Arvidson.
“We already knew it was unlike any place any Mars rover has seen before, even if we don’t yet know how it formed, and now we’re seeing surfaces that look like stone stripes. It’s mysterious. It’s exciting. I think the set of observations we’ll get will enable us to understand it.”
“One possible explanation of these stripes is that they are relics from a time of greater obliquity when snow packs on the rim seasonally melted enough to moisten the soil, and then freeze-thaw cycles organized the small rocks into stripes,” Arvidson said. “Gravitational downhill movement may be diffusing them so they don’t look as crisp as when they were fresh.”
Opportunity has lasted longer, travelled further, and done more than we ever expected, and is still working tirelessly to help us understand Mars. Long may it continue to do so – the elder statesman of Mars.