Opportunity and its twin, Spirit, lasted for years after being sent on a mission expected to run for three months. (Supplied: NASA)
NASA is looking for a final time to contact its record-setting Mars rover Opportunity, before calling it quits.
- Opportunity was designed to last for three months but has survived for 15 years
- It had set and record for endurance on Mars and had also traveled the furthest across the planet – 45 kilometers
- Opportunity's twin spirit was pronounced dead by NASA in 2001 after becoming stuck in the sand
The rover has been silent for eight months, having fallen victim to one of the most intense Martian dust storms in decades.
Thick dust darkened the sky last year and, for months, blocked sunlight from the solar-powered solar panels.
NASA will issue a final series of recovery commands, on top of more than 1,000 already sent.
NASA suspects will be the case – Opportunity will be declared dead, 15 years after arriving at the red planet.
Tweet Spirit and Oppy NASA: "Tonight, we will make our last planned attempts to contact Opportunity." The solar-powered rover last communicated on June 10, 2018, as a planet-wide dust storm swept across Mars.
When did Opportunity fall silent?
NASA last heard from Opportunity on June 10.
Flight controllers tried to awaken the rover, devising and sending command after command for months.
The Martian skies eventually cleared enough for sunlight to reach the rover's solar panels, but there was still no response.
Now it's getting darker and darker on Mars, further dimming prospects.
Engineers speculate the rover's internal clock may have become scrambled during the prolonged outage, disrupting the rover's sleep cycle and draining its batteries.
A growing dust storm on Mars in June, 2018 with the approximate location of Opportunity indicated by the blue dot. (Supplied: NASA)
Opportunity was only expected to last three months
Team members are already looking back at Opportunity's achievements, including confirmation of water once flowed on Mars.
Opportunity was, by far, the longest-lasting lander on Mars.
Besides endurance, the six-wheeled rover set and a roaming record of 45 kilometers.
Its identical twin, Spirit, was pronounced dead in 2011 a year after it had become stuck in the sand and communication ceased.
Both outlived and outperformed expectations, on opposite sides of Mars.
The golf cart sized rovers were designed to operate as geologists for just three months, after bouncing onto our planet's inner cushioning air bags in January 2004.
They were rocketed from Cape Canaveral a month apart in 2003.
It's no easier to say goodbye now to Opportunity than it was to Spirit, project manager John Callas said.
"It's just like a loved one who's gone missing, and you keep holding out hope that they will show up and that they're healthy," he said.
"But every passing day that diminishes, and at some point you have to say enough and move on with your life."
Opportunity and Spirit were not designed to deal with severe weather like dust storms. (Supplied: NASA)
Deputy project scientist Abigail Fraeman was a 16-year-old high school student when Opportunity landed on Mars.
She was in the control center as part of an outreach program.
Inspired, Dr. Fraeman went on to become a planet scientist, joined the NASA's Jet Propulsion Laboratory, and he was a project scientist for Opportunity.
"It gives you an idea of how long this mission has lasted," she said.
"Opportunity's just been a workhorse … it's really a testament, I think, how well the mission was designed and how careful the team was in operating the vehicle."
Global dust storms typically kick up every few years, and "we had gone a long time without one", Mr Callas said.
Unlike NASA's nuclear-powered Curiosity rover, which is still chugging along on Mars, Opportunity and Spirit were never designed to endure such a severe weather.
Ground sloping downward towards the Perseverance Valley on Mars, as seen by Opportunity. (AP: Supplied NASA)
Death in a dust storm and a honored end
Cornell University's Steve Squyres, a leading scientist for both Opportunity and Spirit, believes succumbing to a ferocious storm and a "honourable way" for the mission to end.
"You could have lost a lot of money over the years betting against Opportunity," Professor Squyres said.
The rovers' greatest gift, according to Professor Squyres, was providing a geological record at two distinct places where water once flowed on Mars, and describing the conditions there that may have supported ancient life.
Now it's up to Curiosity and the newly arrived InSight lander to carry on the legacy, Mr Callas said, along with a spacecraft in orbit around Mars.
As for Opportunity: "It has given us a larger world," Dr Callas said.
"Mars is now part of our neighborhood."