Long-lived rover survives its eighth Martian winter

Next task is studying how water carved Perseverance Valley within Endeavor Crater.
By Laurel Kornfeld | Dec 19, 2017
NASA's Mars Opportunity rover, which has functioned continuously since landing on the Red Planet in January 2004, has survived the coldest and darkest parts of its eighth Martian winter.

The coldest months of the Martian year, which is 687 Earth days long, coincided with October and November 2017.

Unlike NASA's larger Curiosity rover, which landed on Mars in August 2012 and is powered by a radioisotope thermoelectric generator that transforms heat produced by the radioactive decay of plutonium into electricity, Opportunity is solar-powered, meaning it has to angle itself toward the Sun in order to recharge.

Because it is located in Mars' southern hemisphere, Opportunity has to face north to receive the sunlight crucial to its ability to power up and stay warm.

Both Opportunity and its twin, Spirit, landed in the southern hemisphere for a mission designed to last three months. In 2009, after five years, Spirit got stuck in soft terrain and was unable to orient its solar panels toward the Sun, leading it to freeze during the ensuing winter.

Opportunity is currently driving through Perseverance Valley, which runs down the inner slope of Endeavor Crater's western rim. The large crater is 14 miles (22 km) wide.

The rover's solar panels are regularly cleaned by the Martian wind and are currently free of dust, noted Opportunity's power subsystem operations team lead Jennifer Herman, who is based at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

While the area has had no major dust storms for 10 Earth years, the fact that the wind keeps cleaning the solar panels means Opportunity will have a good chance of surviving such a storm, Herman said.

During its winter drive through Perseverance Valley, which is believed to have been carved by ancient water, the rover has regularly stopped to recharge at sites facing north.

As the weather warms up, Opportunity will position itself to study the deposits at the bottom of the valley in an attempt to determine the amount of water that once flowed there.

Like winters on Earth, Martian winters vary in their severity, with some having more impact on the rover than others. The impact they have had on Opportunity has varied based on its location.

"I was told not to get too settled in because Spirit and Opportunity probably wouldn't make it through that first Martian winter," Herman said. "Now, Opportunity has made it through the worst part of its eighth Martian winter."

Opportunity was able to stay active during its first winter because it was on the northern slope of a crater. In contrast, it was largely inactive during it fourth winter, in 2009-2010, because it was forced to remain in the same location for 19 weeks.

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