A giant dust storm that now covers nearly the entire southern hemisphere of Mars could permanently jeopardize the future of the Mars Exploration Rovers, officials told Space.com on Thursday.
The new and potentially bleak outlook is a stark shift from the prognosis earlier this week. Michael Malin of Malin Space Science Systems said in e-mail interview that a smaller, second dust storm has recently appeared on the Red Planet, further compounding the threat to the rovers.
The largest dusty squall has reduced direct sunlight to Mars' surface by nearly 99 percent, an unprecedented threat for the solar-powered robotic explorers. If the storm keeps up and thickens with even more dust, officials fear the rovers' batteries may empty and silence the robotic explorers forever.
"This is a scary storm," said Mark Lemmon, a planetary scientist at Texas A&M University and member of the rover team. "If it gets any worse, we'll enter into some uncharted territory. There's been a lot of discussion about what we're going to do if [the rovers] don't have enough power to run during the day."
The storm, first reported by Space.com, hasn't yet reached global proportions, but the dust levels are the thickest the rovers have ever experienced. Lemmon said the conditions rival Mars' global storm of 2001 and another in 1971.
"This thing has been breaking records the past few days. The sun is 100 times fainter than normal," he said. "We're hoping for a big break in the storm soon, but that's just a hope."
Double dusty trouble
In two weeks, the larger dust storm ballooned from a small 230,000 square miles (600,000 square kilometers) to its present size at nearly 7 million square miles (18 million square kilometers), Malin explained. In just a few days, however, its smaller counterpart has emerged as a 3-million-square-mile (7.7-million-square-kilometer) dust bowl. Together, they cover an area larger than the United States, Canada and Greenland combined.
"These large dust events are not a single storm, but are actually made up of a number of local and regional-size dust storms," Malin said. By kicking up enormous amounts of dust, they generate giant dust clouds that can obscure the planet's surface. Once the dust is lifted, he noted, the atmosphere warms and can feed the dust-churning events.
The rover team would be more concerned than at present, Lemmon noted, but early in the storm's genesis, windy conditions swept off light-blocking layers of dust from Spirit and Opportunity.
Caused by Martian dust devils and steady wind, the "cleaning events" doubled the rovers' power to around 800 watt-hours last week and boosted hopes of Opportunity's planned descent into Victoria Crater. As the small storm gathered fury, however, Opportunity's energy-gathering ability has been slashed to a dangerous 280 watt-hours.
"The worst-case scenario is that enough dust in the sky decreases solar energy to the point that we have to shut down too many things to save power," Lemmon said. "The rovers keep their battery alive by keeping their electronics alive."
John Callas, project manager for the Mars Exploration Rover mission at NASA's Jet Propulsion Laboratory in Pasadena, Calif., explained that a dead rover battery could allow cold temperature to maim Opportunity's electronics.
"It's like leaving your laptop out in an Antarctic winter," Callas said. "Soldered joints in the electronics can contract due to thermal contraction. If a rover gets too cold, something essential will fail." Callas explained the situation is unprecedented, so the team isn't certain how much more light-blocking dust the rovers — especially Opportunity — can take.
Fast and furious
Callas said the storm's growth rate was shocking.
"The rovers have weathered weaker storms in the past, which developed over the course of weeks, but nothing like this. This thing came out of nowhere," he said. "The dust levels just skyrocketed."
John Wilson, a planetary scientist who studies Mars' atmosphere at the National Oceanic and Atmospheric Administration in Princeton, N.J., says the topography of Mars' southern hemisphere is probably to blame.
"The southern hemisphere, on average, is about 4 kilometers [2.5 miles] higher than the northern hemisphere, which helps dust storm formation go global," Wilson said, explaining that Earth experiences a similar storm-fueling phenomenon near India. "Tibet is high in regards to mainland India, and so its height helps intensify the Indian monsoon," he said, by generating windier conditions at lower elevations.
"Although the storm threatens the rovers, it's giving us a great opportunity to track another powerful dust storm from start to finish," Wilson said. "We get to see where a storm starts and how it grows, then enter that information into a model to help us predict Martian weather in the future."
Callas noted that global dust storms spawn about every three Martian years (about six Earth years), and the last to occur was about two Martian years ago — so the current storm's potential to become a global event is on cue. If it does, Callas and his team will only be able to cross their fingers.
"The reality of the situation is that we're limited as to what we can do from the ground by cutting power use," Callas said. "If it continues to worsen and stay that way, it's a survivability issue for Opportunity. If Mars wants to kill the rovers, it can."