(CNN) - Last week, a giant dust storm on Mars took up about a quarter of the Red Planet. Now, it's officially "planet-encircling" global dust event, according to NASA.
The solar-powered Opportunity rover stopped communicating with NASA engineers after June 10 because it didn't have enough energy to function, and it put itself to sleep. The rover is maintaining radio silence because the dust has turned day to night on Mars.
Opportunity, in its 15th year of exploration, is the oldest operating rover on Mars. It's riding out the storm in Perseverance Valley, and engineers are hopeful it will awaken after the storm.
Perseverence Valley is the area Opportunity has been observing in order to learn what created the valley, which is a channel carved in the rim by Endeavor Crater. It's been testing to determine whether the valley was sculpted by flowing water, wind erosion or combination of factors. Learning how it was formed could provide insight into the history of the Red Planet.
Luckily, Opportunity isn't alone. It's supported by fellow rover Curiosity and three orbiters high above: the Mars Reconnaissance Orbiter, the 2001 Mars Odyssey and MAVEN. The Mars Reconnaissance Orbiter gave Opportunity's engineers an early warning about the approaching storm and acts like a weather satellite. The other two orbiters can measure the amount of dust and study how the upper atmosphere behaves.
The Curiosity rover, which runs on a nuclear-powered battery, is still tweeting and snapping selfies on the other side of the planet. It's also able to keep NASA engineers updated on the storm.
"Martian haze, all around. The dust storm now circles the whole planet. The measure of atmospheric opacity, or 'tau,' is over 8.0 here in Gale Crater -- the highest I've ever seen. Still safe. Science continues," Curiosity tweeted.
Curiosity remains largely unaffected. It faces the rim of the crater, and photos from its Mast Camera show a hazy sky that is between six and eight times thicker than normal for summer on Mars.
The tau, which is what the haze blocking the sunlight is called, has reached a level of 8 over Gale Crater where Curiosity hangs out. That's a record for Curiosity's recordings. The last measurement over Opportunity's location was a record 11.
Storms are common in the spring and summer on Mars, but sometimes they remain small and last only a week. Other times, like in 2007 and now, they encircle the planet and can last up to two months. The current storm started May 30.
The dust clouds can reach 40 miles or more in elevation, which helps the suspended dust particles circulate and cause a global dust event.
Curiosity and the orbiters are perfectly poised to observe and study this unique storm. The scientists who study Mars have been waiting since 2007 for a chance like this, which will offer an unprecedented look at weather on the Red Planet.
"This is the ideal storm for Mars science," said Jim Watzin, director of NASA's Mars Exploration Program at the agency's headquarters in Washington. "We have a historic number of spacecraft operating at the Red Planet. Each offers a unique look at how dust storms form and behave -- knowledge that will be essential for future robotic and human missions."
"Each observation of these large storms brings us closer to being able to model these events -- and maybe, someday, being able to forecast them," added Rich Zurek, chief scientist for the Mars Program Office at NASA's Jet Propulsion Laboratory in Pasadena, California. "That would be like forecasting El Niño events on Earth, or the severity of upcoming hurricane seasons."
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