Mars Opportunity rover's days are numbered but not all agree they should be

If NASA's longest-serving planetary rover doesn't pick up the phone soon, its missionon Mars may finally be over.

Opportunity is the space agency's workhorse, roving the Red Planetsince 2004 on a mission that was only supposed to last 90 Martian days. (A Martian day, or sol, is about 40 minutes longer than a day on Earth.)

But after an intensedust storm enveloped the planet, communication between Opportunity and Earth was cut off on June 10.

Now NASA has given the energetic rover just overa month to send a signal home, saying that it's still raring to go.

But not everyone agrees with NASA's timeline.

Unravelling Mars' secrets

Opportunity and its twin rover, Spirit, landed on different parts of the planet more than 14 years ago. Their discoveries have since burst open the door to a better understanding of the history of Marsa planet that humans have been racing to reach.

Using the rovers' findings, scientists have come to understand that the dusty, seemingly barren planet was once a wet world, home to an ocean that covered most of its northern hemisphere.

A bit of serendipity has also made the rovers'missions exciting.

In 2007, a limping Spirit one of its wheels damaged and refusing to spin left a deep track in the Martian soil, revealing several bright patches found to be rich in silica.The discovery hinted at evidence of pastconditions that would have been favourable for life, as here on Earth, silica is found around hot, underwater vents often teeming with bacteria.

Spirit's mission formally came to an end in 2011, but Opportunity continued to roll.

Now thisrecent dust storm may be Oppy's biggest challenge yet:It's believed the intense dust covered its solar panels,depriving the roverofthe sunlight it needs to operate.

But a lack of power isn't the only problem. Scientists are also worried about whether Oppy has been able to keep itself warm on a planet wheretemperatures can reach 60 C or colder, which could irreparablydamage thetireless rover.

#SaveOppy

Since the dust storm, NASA has continued tosend signals to Opportunity, waiting for it to answer.So far, it has been met with silence.

The agency thenfaced a question: How long is too long to keep calling, waiting for Opportunityto pick up?

At the end of last month, NASAcame up with a plan.

With the Martian atmosphere more opaque than normal a measurement referred to as tau the scientists decided to wait until the dust had cleared enough to let some sunlight reliably reach the rover. Then the team would start a 45-day period of "active listening," nudging Opportunity by sending it commands.After that time, they willgo into "passive listening" mode, where the signals stopand the rover's frequencies will simply bemonitored to see if Opportunity is calling them instead.

The countdown clock started ticking on Sept. 11.

The decision has caused an uproar among both some of the public and those who have worked on the rovermissions.

The arguments for extending the deadline past the 45 days are largely two-fold:

• Some team members believe that the best time for a "cleaning event" where winds on Mars can blow dust off the rover's solar panels will come after the 45-day period wraps up. If no one is actively listening, a call home from Opportunity might be missed.
  
• When Spirit lost communication with Earth in 2010, it was given far longer 10 months to pick up the calls from Earth.

But Steve Squyres, the principal investigator for the Mars Exploration Rover mission, said Spirit's situationwas an entirely different scenarioand that cleaning events aren't guaranteed.

"In the case of Spirit, we had made a mistake," he said. "Without correcting that problem, the vehicle would wake up and then bang go back to sleep without sending us anything. So the only chance we had to hear from Spirit was by active listening."

It's a cute, adorable, intrepid, dutiful little creature. It's a machine, but it exhibits human-like qualities. It explores, it discovers and it shares that with us.- John Callas, Opportunity mission manager

Opportunity mission manager John Callas has denied that the recommendations from team members were ignored.

"I know there are a couple of people out there saying their ideas weren't considered," he said. "They were considered and they were rejected,and there are good technical reasons why they weren't accepted. Unfortunately, they don't seem to accept that."

Some in the space community have taken to social media,most notably Twitter, to express their hopes thatOpportunity will wake up, or be given a longer timeline.Hashtags like #SaveOppy and #WakeUpOppy are circulating, and nearly 8,000 digital postcards have been sent to Opportunity.

A much-loved rover

Much of thatcomes from an emotional attachment to a rover that has been a large part of some people's lives, Callas said, including those who havespent their entire careers working on Spirit and Opportunity.

"People are very attached to this roverI mean, they've anthropomorphized it," Callas said. "It's a cute, adorable, intrepid, dutiful little creature. It's a machine, but it exhibits human-like qualities:it explores, it discovers and it shares that with us."

And despite the fact that Opportunity haslived 5,119 sols past "warranty" to date, some feel the roverstill has more left.

"My biggest fear is just leaving a perfectly functional vehicle on the surface of Mars, that's just sitting there waiting for commands to be sent to it, that is actively transmitting and we're just not listening," said Mike Seibert, a former lead spacecraft systems engineerand driver for Spirit.

"That would be the absolute worst way to end this mission."

NASA offered Opportunity's supporters some hope on Sept. 11, when the agencyupdated its original statementas the clock started counting down: "[After the 45 days], the team will report to NASA HQ to determine whether to continue with the strategy or adjust it."

And those who workon the mission remainhopeful that the roverwill continue to outperform expectations.

"This is the toughest thing the rover has ever been throughno question about that," said Squyres. "But you could have lost a lot of money over the years betting against Opportunity."