A rendering of NASA's Opportunity roverImage: NASA

Right now, NASA's Opportunity rover is doing its best to weather an intense dust storm on the surface of Mars — one that could prevent the robot from ever phoning Earth again. The storm is so bad that the dust is blotting out the Sun, making it hard for Opportunity to get the light it needs on its solar panels, which generate power and charge the robot's internal battery. Engineers at NASA are waiting to see if the rover can make it through the storm and still function once the dust has settled.

The good news is that Opportunity is a hardy space bot. After landing on the Red Planet in January 2004, the rover has lasted for more than 14 years on Mars, much longer than its planned three-month mission. Plus, the rover survived another Martian dust storm back in 2007, so engineers know what it takes to get through one of these events.

It's almost as if the daytime has turned into night

The bad news is that the 2007 storm was nowhere near as bad as the one that's happening now. This storm took engineers by surprise. It formed right above the rover on June 3rd, with little notice, and it's quickly strengthened since then. As of this weekend, the storm is so dusty that the skies on Mars are much darker than they were when the other storm hit a decade ago. It's almost as if the daytime has turned into night. And because of this, Opportunity is generating the lowest amount of power it's ever collected on Mars, according to a source at NASA familiar with the matter.


— Doug Ellison (@doug_ellison) June 11, 2018

A chart showing different levels of opaqueness on Mars, represented by tau values. Over the weekend, the storm's estimated tau value was 10.8.

With such low power generation, Opportunity must dip into its battery reserves to continue working. But if the battery's voltage gets too low, Opportunity may not be able to communicate with engineers on the ground throughout the rest of the storm, and NASA will no longer know what state the robot is in. That's scary because engineers will have no idea if the rover is getting too cold while it deals with the dust. Just moving around a little bit each day heats Opportunity's battery up enough to function in the frigid Martian environment. But if Opportunity's reserves get too low, it won't be doing any movement for the rest of the storm. The rover does have heaters on board to provide necessary warmth if the battery's temperature drops too low, but the heaters also need power to function. It's a Catch-22.

To combat the storm, NASA has stopped all science activities on Opportunity and turned off most of its instruments. All the rover has to do now is recharge as much as it can for most of the day, then wake up every so often to communicate with Earth, and take a picture of the Sun to show how bad the storm is. So far, it seems like Opportunity still has enough power to do these basics. On Sunday, June 10th — a week after the storm formed — NASA engineers received a normal transmission from the rover and were able to give it some commands.

This storm hit us by surprise. But by chance we happened to be in about the best configuration possible to weather this storm. Another saving grace is dust storms trap heat, so it won't get as cold at night.

— Keri Bean (@PlanetaryKeri) June 11, 2018

But things may soon change. As Opportunity dips into its battery storage, the rover will go into what's known as a "low power fault mode." In this state, the bot operates on a very simple autopilot: it remains off for most of the day, only waking up during certain predefined windows of time to listen for commands from Earth. It won't even take pictures.

For now, engineers believe Opportunity is not in "low power fault mode" yet, according to the NASA source. But it's also possible that Opportunity's power has gotten so low that it's skipped the fault mode entirely and has entered a rolling brownout. If that's the case, Opportunity may not communicate at all for a while, or only communicate sporadically when it's gathered enough power over longer periods of time. NASA has requested additional time with the Deep Space Network — a global system of communication antennas here on Earth — to better listen for transmissions from the rover.

If the rover does lose communication with Earth, NASA is in the dark. Engineers won't know what type of condition Opportunity is in or if it's getting too cold and the robot is in danger of breaking. Extreme cold is a big concern: low temperatures are what caused Opportunity's twin, the Spirit rover, to cease functioning on Mars in 2010.

A map of the growing dust storm on Mars, taken on June 6thImage: NASA

Fortunately, Opportunity entered this storm under the best circumstances. The rover is near the equator on Mars, where summer is about to begin. Plus, dust storms can act like a big blanket on the Martian atmosphere, absorbing the Sun's heat and warming up the planet. So it's possible that Opportunity may make it through this relatively unscathed. It may eventually shut down for the duration of the storm only to wake back up in a stable condition once the Sun is shining again.

The storm, however, could last a while. It's been growing in size, and there are signs that it could eventually span nearly the entire Martian globe. If that happens, the storm could last as long as month or more, which was the case for the 2007 storm. That means NASA could be in for a long month of June, as it waits to learn the ultimate fate of one of its hardiest rovers.