In March of that year, the Martian winds started blowing and researchers noted an increase of energy supply to the Spirit from 210 watt-hours to 240 watt-hours as the winds blew away the dust covering the rover. This became known as a 'cleaning event'.
There was a similar cleaning event in 2007, but that one was not as helpful because a dust storm shortly after, covered the Spirit in dust again and undid all the good the wind did in cleaning the rover.
After the 2009 cleaning event Colette Lohr, a rover mission manager at NASA's Jet Propulsion Laboratory explained the benefits of cleaning events: "We will be able to use this energy to do significantly more driving. Our drives have been averaging about 50 minutes, and energy has usually been the limiting factor. We may be able to increase that to drives of an hour and a half."
These cleaning events on Mars are very significant considering that the rovers were only expected to last 90 Martian days. Instead of operating for three months before running out of energy, rover Opportunity is still active 10 years after landing!
