December 10, 2018

Growing dust storm encircles Mars, rover remains silent


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A self-portrait taken by NASA’s Curiosity rover taken June 15. A Martian dust storm has reduced sunlight and visibility at the rover’s location in Gale Crater. Credit: NASA/JPL-Caltech/MSSS

The effects of a global dust storm on Mars have been observed by NASA’s plutonium-powered Curiosity rover, which continues its scientific campaign as the thick veil of dust continues starving the aging Opportunity rover of solar energy on the other side of the planet.

The dusty conditions have not limited any of Curiosity’s activities because it draws electricity from a radioactive power source, but images returned by the rover in recent days show distant ridges disappearing in an orange haze.

The storm’s impact on Opportunity is a different story. Ground controllers last received a signal from Opportunity on June 10, and engineers believe the rover tripped a low-power level and went into sleep mode, waiting for its batteries to charge sufficiently to radio engineers on Earth.

On Tuesday, NASA said the dust storm had encircled the Red Planet with global coverage, and a fleet of orbiters circling Mars are surveying the storm’s evolution. Curiosity is acting as a dust storm research outpost on the surface, monitoring weather changes as it continues its primary science mission of studying Martian geology.

Opportunity’s master clock is designed to wake up the rover periodically to check its battery charge. But the rover will go back to sleep if the batteries do not hold enough electrical charge, and the clock will set a new time to wake up for another battery check.

If power levels plummet too low, the clock itself will stop running, but the rover’s on-board software is programmed to switch on Opportunity’s computer automatically once its batteries are sufficiently charged. In such a case, the computer would check to see when the sun is in the sky, then attempt to send a signal to Earth.

Opportunity carries eight radioisotope heater units — each using the radioactive decay of plutonium to produce about one watt of heat — to keep the rover’s internal electronics from getting too cold. NASA officials said last week the dust storm has raised global temperatures on Mars, and engineers believe the rover can withstand the freezing temperatures it was expected to encounter during hibernation.

“A recent analysis of the rover’s long-term survivability in Mars’ extreme cold suggests Opportunity’s electronics and batteries can stay warm enough to function,” NASA officials wrote in an update Wednesday. “Regardless, the project doesn’t expect to hear back from Opportunity until the skies begin to clear over the rover. That doesn’t stop them from listening for the rover every day.”

Artist’s concept of the Opportunity rover on Mars. Credit: NASA

Before the dust storm hit, Opportunity was exploring a valley lining the slope of Endeavour Crater, helping scientists investigate whether the feature formed from a water, ice or debris flow, or from wind erosion.

Opportunity landed on Mars on Jan. 25, 2004, to begin a planned 90-day mission. The rover’s twin, named Spirit, touched down on the Red Planet three weeks before Opportunity, and continued its mission until March 2010.

The long-lived Opportunity rover has driven more than 28 miles (45 kilometers) since landing, visiting multiple impact craters across a broad plain named Meridiani Planum.

NASA said Wednesday that the ongoing dust storm is comparable in scale to a storm observed by the Viking 1 lander in 1977, but is not as extensive as a 2007 storm that Opportunity previously weathered. It’s also different from large dust storms observed by the Mariner 9 and Mars Global Surveyor orbiters in 1971, 1972 and 2001.

“Those storms totally obscured the planet’s surface, save for the peaks of Mars’ tallest volcanoes,” NASA said in an update Wednesday. “The current dust storm is more diffuse and patchy; it’s anyone’s guess how it will further develop, but it shows no sign of clearing.”

At Curiosity’s science station in Gale Crater, the rover has measured the thickest sunlight-blocking haze it has encountered since landing in August 2012. But Opportunity measured even an thicker haze before going into hibernation earlier this month.

Scientists first detected the dust storm May 30, and they do not know when it will abate. Some of the strongest Martian dust storms can stay active for weeks or months.

But researchers hope data gathered on the current dust storm will help predict similar events in the future. NASA and its international partners — Europe and India — have the largest fleet of spacecraft at Mars in history, enabling the collection of a wide array of measurements.

“Each observation of these large storms brings us closer to being able to model these events — and maybe, someday, being able to forecast them,” said Richard Zurek, chief scientist for the Mars Program Office at NASA’s Jet Propulsion Laboratory, in a statement. “That would be like forecasting El Niño events on Earth, or the severity of upcoming hurricane seasons.”

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Follow Stephen Clark on Twitter: @StephenClark1.


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