https://phys.org/news/2018-07-image-mars-storm.html

The intensity of this major event means very little light from the Sun reaches the martian surface, a situation extreme enough that NASA's 15-year old Opportunity rover has been unable to recharge its batteries and call home: it has been in hibernation mode since mid-June.

Dust storms on Mars occur regularly during the southern summer season when the planet is closer to the Sun along its elliptical orbit. The enhanced solar illumination causes stronger temperature contrasts, with the resulting air movements more readily lifting dust particles from the surface – some of which measure up to about 0.01 mm in size.