NEW YORK, June 22 (Xinhua) -- The giant dust storm on Mars that has prevented NASA's exploration rover Opportunity from conducting scientific work last week is now officially a global dust event, the U.S. space agency said Thursday.

"The Martian dust storm has grown in size and is now officially a 'planet-encircling' (or 'global') dust event," the National Aeronautics and Space Administration (NASA) said in a statement.

The solar-powered Opportunity, launched in 2003 as part of NASA's Mars Exploration Rover program, stopped its communication with engineers on Earth after June 10 because it is blotted out by dust at its current location.

Luckily, its fellow rover Curiosity is still working, sending tweets and taking selfies on the other side of the planet.

While Opportunity is powered by sunlight, Curiosity has "a nuclear-powered battery that runs day and night," according to NASA.

Dust has steadily increased over the Curiosity rover, more than doubling over the weekend, NASA said.

"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 Thursday.

According to the U.S. space agency, this is not the first time that an enormous dust storm encircles the whole planet.

"The last storm of global magnitude that enveloped Mars was in 2007," NASA said.