page_title: Cleaning event
hierarchical_section_title: Cleaning event
caption_attribution_description: From press release: Dusty Solar Panels on Spirit The deck of NASA's Mars Exploration Rover Spirit is so dusty that the rover almost blends into the dusty background in this image assembled from frames taken by the panoramic camera (Pancam) during the period from Spirit's Sol 1,355 through Sol 1,358 (Oct. 26-29, 2007). Dust on the solar panels reduces the amount of electrical power the rover can generate from sunlight each sol. Earlier self-portraits by Spirit, such as one taken on Sol 586, offer a comparison view of cleaner solar panels. The vertical projection used here produces the best view of the rover deck, though it distorts the ground and antennas somewhat. The eight-pointed star shape near the front of the rover (bottom of the image) marks the location of the camera mast, which is out of view of the Pancam atop the mast. This mosaic view in approximate true color is a composite of frames taken through the Pancam's filters centered on wavelengths of 600 nanometers, 530 nanometers and 480 nanometers.
context_page_description: A cleaning event is a phenomenon whereby dust is removed from solar panels, in the context of exploration and science rovers on Mars, supposedly by the action of wind. The term cleaning event is used on several NASA webpages; generally supposing that Martian winds have blown dust clear off the probes on Mars, including the solar panels which power them, increasing their energy output. The nature of the cleaning events is not known, but the assumption is that wind blows the dust off the panels. Cleaning events were discovered in 2004 when several times power levels increased by 5% overnight, in contrast to the expectation they would decrease—the added power allowed the missions to continue beyond their expected lifetime. One theory is that wind currents in craters aid in cleaning events, and also if the rover is sloped, this is speculated to help remove dust.
  The term started being used in 2004 as the Mars Exploration Rovers' solar panels started to benefit from these events. The rovers were expected to last about 90 sols on Mars, after which dust would cover their solar panels and reduce solar power to levels too low for the rovers to operate.
context_section_description: A cleaning event is a phenomenon whereby dust is removed from solar panels, in the context of exploration and science rovers on Mars, supposedly by the action of wind. The term cleaning event is used on several NASA webpages; generally supposing that Martian winds have blown dust clear off the probes on Mars, including the solar panels which power them, increasing their energy output. The nature of the cleaning events is not known, but the assumption is that wind blows the dust off the panels. Cleaning events were discovered in 2004 when several times power levels increased by 5% overnight, in contrast to the expectation they would decrease—the added power allowed the missions to continue beyond their expected lifetime. One theory is that wind currents in craters aid in cleaning events, and also if the rover is sloped, this is speculated to help remove dust.
  The term started being used in 2004 as the Mars Exploration Rovers' (MER) solar panels started to benefit from these events. The rovers were expected to last about 90 sols (Martian days) on Mars, after which dust would cover their solar panels and reduce solar power to levels too low for the rovers to operate. However, power levels went back up due to the cleaning events caused by the winds in the Martian atmosphere. Periodic cleaning events have allowed the MERs to operate far longer than the planned 3 months. The Spirit rover finally ceased operation in early 2010, and the Opportunity rover remained active until mid 2018, more than 14 years after landing.
  Cleaning events can either be rapid, such as overnight, or over many days where solar power slowly goes up. For example, with the MER-A Spirit rover, on 18 and 28 April 2009, the power output of the solar arrays was increased by cleaning events. The power output of Spirit's solar arrays increased from 223 watt-hours per day on 31 March 2009 to 372 watt-hours per day on 29 April 2009. Spirit had experienced multiple cleaning events during its operation that aided in its mission extension. However, the lack of cleaning events was noted as a factor in its demise.
  Other factors that affect solar power output include the opacity of the Martian atmosphere and Martian seasonal changes; however, this does not account for the directly observable removal of dust from the upper surfaces of the rovers as shown in the images.
  The Materials Adherence Experiment had a glass plate that allowed the dust to be cleared off and protected a Gallium arsenide photo-cell. It was part of the Mars Pathfinder program in the 1990s. This allowed the rate at which dust accumulated to be measured.
caption: Circular projection showing MER-A Spirit's solar panels covered in dust in October 2007 on Mars. Cleaning events have periodically increased power from the solar arrays.
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