The Mars Rovers Spirit and Opportunity landed on the Red Planet 14 years ago in January 2004.
Mars rover Spirit was active from 2004 until 2010 greatly exceeding its 90 day planned mission duration. Mars rover Opportunity is still going strong to this day exceeding its 90 day mission time by over 14 years.
Each rover was designed to be powered by solar panels that supply 140 watts of power when fully illuminated by the midday Sun. These panels charge a 7 kg lithium ion battery which is used to power the systems on the rovers through the night.
Mars is very dry, it has a thin atmosphere is a very dusty place. It was expected that the solar panels would slowly get covered in dust and supply less power over time eventually becoming totally useless.
This was largely true until someone accidentally let the janitor onto the fake NASA Mars set and he accidentally cleaned up the dirty solar panels causing the power output from the panels to be restored to near original condition (this set is right beside the fake Moon landing set in Area 51).
Credit: NASA/JPL/Caltech link Public domain image.
Okay, putting the joking aside the solar power panels were cleaned but not by any janitor on a fake Mars set. They were cleaned off by wind gusts or maybe even dust devils in an unanticipated phenomenon called a cleaning event.
A cleaning event is self explanatory phenomenon in which the dust on solar power panels is removed by some postulated atmospheric event. The most likely hypotheses are either just a simple strong gust of wind or a dust devil passing over the location of a rover.
The atmospheric pressure on Mars is about 0.6 kPa in comparison to the atmospheric pressure on Earth which is around 100 kPa (about 150 times thicker). So the Martian atmosphere is pretty thin but still capable of gusts of wind as well as dust devils as you can see in the image above.
These cleaning events have been absolute life savers for the rovers allowing them to get 'power-ups' and to avoid the inevitable decline in power output and the subsequent end of mission. The cleaning events can either be rapid (over the course of a night) or slow (over the course of a few days). These events have occurred randomly on multiple occasions providing an ongoing source of renewed power output for the rovers.
Credit: NASA/JPL/Caltech link Public domain image.
The remarkable thing about the cleaning events which is apparently not fully explained is that intricate surfaces (i.e. the nooks and crannies) are also apparently cleaned as well.
It is remarkable that a wind or dust devil in such a thin atmosphere would be able to clean off the rovers so well. On the other hand if you think about it, any dust that is light enough to be carried by a thin atmosphere should also be able to be blown away very easily. It might imply that Martian dust is finer than flour and very easily blown around.
Also I suspect that the moisture content in the Martian atmosphere is very low so this dust cannot get wet and adhere to any surfaces. It is always lightly attached to the surfaces and able to be easily dislodged by vibrations from moving around the surface as well as the wind.
Closing Words
I would have liked to see the faces of the Mars rover systems engineer when he or she came into work that morning and read over the rover's system performance for the day only to see that the power output had jumped up dramatically. There definitely would have been lots of head scratching and double checking of the data that morning.
Eventually someone would have suggested taking a picture of the rover itself to see if any dust was actually removed from the solar panels. They would then have had to wait for an interminable period of time until the results came in to show a nice clean looking Mars rover.
I think that these cleaning events indicates that Martian dust is incredibly light and incredibly fine. This means that when a team of astronauts finally land on Mars to live and work on the Red Planet that THIS STUFF IS GOING TO GET ABSOLUTELY EVERYWHERE.
Thank you for reading my post.
Post Sources
https://en.wikipedia.org/wiki/Mars_Exploration_Rover
https://en.wikipedia.org/wiki/Spirit_(rover)
https://en.wikipedia.org/wiki/Opportunity_(rover)
https://en.wikipedia.org/wiki/Cleaning_event
https://en.wikipedia.org/wiki/Dust_devil
https://en.wikipedia.org/wiki/Mars