June 11 (UPI) -- NASA's Opportunity rover is currently hunkered down, waiting out a severe dust storm on Mars. On Sunday, the rover sent a transmission back to Earth, letting NASA engineers know the rover still has enough battery life for basic communication.
Opportunity is currently inside Mars' Perseverance Valley. The valley and surrounding region have been shrouded by an intensifying dust storm over the last several days.
Like all Martian spacecraft, Opportunity uses solar panels to keep its batteries charged. Dust storms can block out the sun for days, making it near impossible for the rover to recharge.
"Science operations for Opportunity are temporarily suspended while it waits out a Martian dust storm," the Mars rovers' account announced on Twitter. "The dust in the atmosphere is impacting the amount of power generated by the rover's solar panels."
Scientists gauge the strength of a dust storm using the unit tau, a measurement of the atmosphere's opacity. In 2007, Opportunity weathered a large dust storm with a tau of 5.5. As of Sunday morning, the current dust storm boasted a tau of 10.8.
Opportunity's original mission was expected to last just 90 days, but the rover is still operational nearly 15 years later. It's a hardy machine, but the latest conditions are challenging its grit.
Engineers are closely monitoring its battery levels and temperature. Nighttime on Mars is extremely cold, but using Opportunity's heaters can drain the batteries. It's a balancing act.
"Its heaters are vitally important to keeping it alive, but also draw more power from the battery," NASA wrote in a recent update. "Likewise, performing certain actions draws on battery power, but can actually expel energy and raise the rover's temperature."
Dust storms on Mars are a well known phenomenon but are infrequent. However, they can develop seemingly overnight and last weeks, even months. During the southern hemisphere's summer, Martian dust rises higher into the atmosphere as its heated. The updrafts of dust can trigger more winds, triggering a feedback loop that fuels the birth of a dust storm.
The current dust storm, which first emerged on June 1, now spans 7 million square miles -- bigger than North America.
NASA scientists will continue to monitor Opportunity's status using the agency's Martian orbiters, MRO, Odyssey and MAVEN, as well as NASA's Deep Space Network.