At least six different dust devils appear in the images, some of them in more than one image. They range in diameter from about 2 meters (7 feet) to about 5 meters (16 feet).
“It will be very interesting to watch over the next days and weeks to see if there are lots of dust devils or if this was an isolated event,” Lemmon said.
The Phoenix team is not worried about any damage to the spacecraft from these swirling winds. “With the thin atmosphere on Mars, the wind loads we might experience from dust devil winds are well within the design of the vehicle,” said Ed Sedivy, Phoenix program manager at Lockheed Martin Space Systems Company, Denver, which made the spacecraft. “The lander is very rigid with the exception of the solar arrays, which once deployed, latched into position and became a tension structure.”
Phoenix monitors air pressure every day, and on the same day the camera saw dust devils, the pressure meter recorded a sharper dip than ever before. The change was still less than the daily change in air pressure from daytime to nighttime, but over a much shorter time.
“Throughout the mission, we have been detecting vortex structures that lower the pressure for 20 to 30 seconds during the middle part of the day,” said Peter Taylor of York University, Toronto, Canada, a member of the Phoenix science team. “In the last few weeks, we’ve seen the intensity increasing, and now these vortices appear to have become strong enough to pick up dust.”
However, I've been taking a closer look at these photographs, and I believe I can see a rotund robot driving a utility vehicle in the distance. Start the following video at about 1:35 to see what I mean. Turn the sound off, though; someone added a voice-over for Robby that is not particularly good or useful.