The martian dust storm that put the Opportunity rover to sleep in early June has by now intensified into a Planet-Encircling Dust Event, or PEDE, that would cover both North America and Russia completely if it were on Earth.
Though its current location is nowhere near Opportunity’s, the Curiosity rover (currently studying Gale Crater) captured the growing impacts of the storm in a selfie snapped June 15.
The dust storm, though not unexpected, is a bit untimely — Mars is quickly approaching opposition in July, with its closest approach to Earth occurring shortly after. This setup normally affords excellent views of the planet’s surface features, which certainly won’t be the case if it’s buried under a thick cloud of dust. Regional dust storms are common, but scientists aren’t entirely sure what causes them to occasionally grow into PEDEs. The planet’s dust storms are typically prompted by warming as the planet approaches its closest point to the Sun; temperature contrasts generate winds that pick up and spread fine surface dust grains. As the polar ice caps melt, the additional carbon dioxide in the atmosphere increases surface pressure and suspends the particles in the air, sometimes in clouds reaching up to 40 miles (60 kilometers) high.