A massive dust storm on Mars, which circled the planet since late May - and even halted operations for the Opportunity rover - is starting to lift.
As the skies clear over Opportunity's resting spot in Mars' Perseverance Valley, NASA engineers at the organisation's Jet Propulsion Laboratory (JPL) in California believe solar-powered rover will soon receive enough sunlight to automatically initiate recovery procedures.
NASA said the Opportunity rover mission team has developed a two-step plan in preparation for better weather in a bid to provide the highest probability of successfully communicating with the rover and bringing it back online.
"The Sun is breaking through the haze over Perseverance Valley, and soon there will be enough sunlight present that Opportunity should be able to recharge its batteries," said John Callas, Opportunity project manager at JPL.
"When the tau level [a measure of the amount of particulate matter in the Martian sky] dips below 1.5, we will begin a period of actively attempting to communicate with the rover by sending it commands via the antennas of NASA's Deep Space Network. Assuming that we hear back from Opportunity, we will begin the process of discerning its status and bringing it back online."
The rover's last communication with Earth was on 10 June, and the current health of the rover is unknown. Its engineers are relying on the expertise of Mars scientists who have been analysing data aboard NASA's Mars Reconnaissance Orbiter (MRO) to estimate the tau near the rover's position.
"The dust haze produced by the Martian global dust storm of 2018 is one of the most extensive on record, but all indications are it is finally coming to a close," added MRO Project Scientist Rich Zurek.
"Images of the Opportunity site have shown no active dust storms for some time within 3,000 kilometers [about 1,900 miles] of the rover site."
With skies clearing, mission managers are hopeful the rover will attempt to call home, but they are also prepared for an extended period of silence.
"If we do not hear back after 45 days, the team will be forced to conclude that the Sun-blocking dust and the Martian cold have conspired to cause some type of fault from which the rover will more than likely not recover," said Callas.
"At that point our active phase of reaching out to Opportunity will be at an end. However, in the unlikely chance that there is a large amount of dust sitting on the solar arrays that is blocking the Sun's energy, we will continue passive listening efforts for several months."
However, while the situation in Perseverance Valley is critical, the rover team is optimistic, knowing that Opportunity has overcome significant challenges during its 14-plus years on Mars.
"In a situation like this you hope for the best but plan for all eventualities," added Callas. "We are pulling for our tenacious rover to pull her feet from the fire one more time."
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