From small dust devils to regional dust storms to massive global storms covering the entire world. Mars sees it all. And scientists have a handle on many of the patterns that shape them. But like the weather here closer to home, the moment you think you have it figured out – you get a surprise.

A few weeks ago, a regional dust storm began to take shape in the Acidalia area of northern Mars. It blew southward where it turned into a huge storm bigger than the United States. It wasn’t too big of a deal. Dust storms often form during spring and summer in Mars’ southern hemisphere (it’s mid-summer now). Plus, the development path followed a pattern scientists are used to seeing.

Mars dust storm vid

What surprised scientists is what they saw last week. A second storm began brewing in the same location as the one a few weeks ago. “What’s unusual is we’re seeing a second one so soon after the first one,” said Mars meteorologist Bruce Cantor of Malin Space Science Systems. The company built the Mars Color Imager (MARCI) aboard NASA’s Mars Reconnaissance Orbiter (MRO).

“We’ve had orbiters watching weather patterns on Mars continuously for nearly two decades now, and many patterns are getting predictable, but just when we think we have Mars figured out, it throws us another surprise,” Cantor added.

Meteorologists on Earth feel your pain, Bruce. New York City was supposed to be in the midst of a blizzard. Instead, the blizzard warning was canceled early this morning. Hey, you get the snow day without the crippling snow. Win-win.

This second storm has a small chance of becoming a global storm last seen in 2007, but it’s not expected to. Most regional storms that morph into global storms occur earlier in the summer. Still, it’s something for Martian meteorologists to keep an eye on.

It’s not just MRO scientists keeping close tabs on the storm. The team responsible for the Opportunity rover is also watching closely. But, a dust storm isn’t all bad news. In fact, the increase in wind can be helpful. Back in late February, when the first dust storm was intensifying, the Opportunity received a good cleaning of its solar panels. This resulted in an energy output bump of more than 10%. Not bad considering the usual dust cleaning from storms results in just a one or two percent increase.

dust storm approaching rover

Since the first storm swept through, the sky has become dustier with some of the dust falling back onto the solar panels.

Scientists will have to wait and see how Opportunity looks once the second storm sweeps through and dissipates.

“Before the first regional dust storm, the solar panels were cleaner than they were during the last four Martian summers, so the panels generated more energy,” said JPL rover-power engineer Jennifer Herman. “It remains to be seen whether the outcome of these storms will be a cleaner or dirtier Opportunity. We have seen both results from dust storms in the past.”

The last global dust storm on Mars

In 2007, Mars looked more like a gas giant then the rocky planet we are used to seeing. Here’s a comparison image from the global dust storm in 2001. The image on the left was taken a month before the image on the right.

Mars global dust storm

At the time, Mars rovers Spirit and Opportunity had to batten down the hatches. With dust blocking out most of the sunlight, normal operations were halted as both rovers drastically reduced their power consumption for a few weeks. Each day, the two rovers would power up just long enough to warm them up. Then, they would switch off again.

The good news is, global dust storms on Mars don’t last that long. Transforming into a global dust storm is the beginning of the end for the weather phenomenon. Heat reaching the red planet’s surface is the main driving force for dust storms. As sunlight hits the ground, it heats the air closest to the surface. The air above it remains cool. As the two air masses collide, warm air rises bringing dust with it.

With most of the light blocked from hitting the surface, the global dust storm eventually fades away.

The global dust storms are still a mystery to scientists. They’re not sure why there’s such a long period between dust storms.

Last year, James Shirley (a planetary scientist at NASA’s JPL) published a prediction that a global dust storm will begin within a few weeks or months of October 29th, 2016. About four months later and we’re still waiting. We’ll see if the latter half of Mars’ summer (in the southern hemisphere) has a surprise in store for us.

Image credits: NASA