Initially intended for a 90-day mission, which included investigating for evidence of water on Mars, the Opportunity rover landed on the Red Planet in 2004 and has since operated for fourteen years. However, it looks like this service record may soon come to an end.
On May 30, a dust storm began – a common occurrence on Mars, except this one encompassed the entire planet within a month. Opportunity relies on solar panels for power, so, with the sky dark, it entered hibernation mode on June 10 to conserve energy. Comparatively, the more modern Curiosity rover, powered by heat from an on-board radioactive sample, was unaffected.
For the rover’s operators at Caltech’s Jet Propulsion Laboratory (JPL), this was not immediately a cause for concern. The rover is designed to ‘awaken’ at regular intervals to accept commands. During these times, the science team at JPL use NASA’s Deep Space Network (DSN) to listen for signals from the rover that indicate it is still operational. Additionally, three times a week they send a command outside of the usual window to elicit a ‘beep’ from the rover, in case it’s awake at an unexpected time. This is called ‘active listening’.
However, despite giving off regular pings, Opportunity has not responded. The storm reached its peak in June and has since cleared significantly, so the rover’s continued silence has raised concerns that it has been permanently rendered inoperable by the dust and cold.
In light of this, on August 30, JPL Opportunity project manager John Callas announced a timeline. Once the tau level – a measure of atmospheric opacity in the Martian sky – dropped below 1.5 (it reached 10.8 at the storm’s peak), Opportunity would be given 45 days of active listening. If no response was heard, JPL would then be forced to declare the rover dead.
Although Callas’s statement is realistic, some would argue that it is fatalistic. Reportedly, Opportunity team members were not consulted about the deadline or given prior notice of the August 30 announcement. Many team members felt that cutting active listening after 45 days would be giving up on Opportunity too soon. Former Opportunity director Mike Seibert remarked, “it just seems like it’s an easier thing to say we’re done than putting the extra effort into soldiering on…”
Indeed, over the fourteen years, JPL has already seen Opportunity endure far more challenges than anticipated. The rover has lasted more than 55 times its expected lifetime; designed to travel about 1000 metres, it has logged 45 kilometres and become the furthest-travelled vehicle on any moon or planet besides Earth. Its unplanned longevity is owed to an unexpected Martian phenomenon, discovered only after the rover arrived on Mars. Every Martian year, the planet experiences a windy season lasting about two Earth months. Strong gusts of wind, called ‘cleaning events’ or ‘dust devils,’ can clean accumulated dust off the rover’s solar panels. If not for these devils, Opportunity would have lost power long ago.
This year, the windy season is expected to come in November and last until January. But, if the tau level drops soon, the 45-day deadline will not be enough time to last the whole season.
It appears that the Opportunity team believes that the short deadline is due to economic concerns. Opportunity science team collaborator Tanya Harrison commented, “in the grand scheme of things, [dust devil season] is not that long from now… you’re not going to suddenly be saving tens of millions of dollars by cutting the mission short.” However, Callas seems to think the windy season will not help. His announcement emphasises that it is unlikely that dust build-up on the solar panels is the sole reason for Opportunity’s silence – even if the wind can clean the dust, the rover has also likely suffered permanent damage that will prevent it from rebooting. But, Callas is not blind to the emotional impact on his team: “It’s just like a loved one that’s missing in action… you still hold out hope, and we are. We’ll still listen. But we have to be realistic, too…”
The experience is particularly acute for the team because they have been through it before. Spirit, the sister rover to Opportunity and part of the same Mars Exploration Rover (MER) mission, fell silent in March 2010. Like Opportunity, it’s inability to be solar-powered led to Spirit’s untimely fate. In May 2009, it became stuck in a position where it could not face the sun. The rover could not run its heaters, and when the Martian winter came, the cold left it inoperable.
According to Seibert, Spirit’s chances were far worse than Opportunity’s are now, yet Spirit was given much more time – it was May 2011 before attempts to re-establish contact were halted and the rover was declared dead. “We did everything we could have done,” he said.
This time, the stakes are higher. Regarding Spirit‘s loss, Seibert said: “It was just losing half of the spacecraft, but there was still plenty to do”. Now, if Opportunity remains silent, the MER mission comes to a close. The team is understandably anxious for this not to happen anytime soon.
However, even if it the operation must conclude, Opportunity’s life has had no shortage of extraordinary discoveries. In its first few weeks on Mars, it uncovered small, highly spherical pieces of the mineral hematite in the soil. The discovery of hematite was critical, as it is the mineral form of rust which usually forms in water. However, it was likely formed in highly acidic water that would be difficult for life to survive in. In 2011, Opportunity also detected smectite, a clay mineral, in the Endeavour Crater. Like hematite, smectite forms in water – specifically water with a neutral pH – thereby providing much stronger evidence for the possibility of life on Mars.
Perhaps in fifty years, when Mars seems as close as the moon does now, we will look back at Opportunity’s discoveries and be amazed that they were made by a robot controlled from fifty million kilometres away.