Posted: September 12, 2008
"We expected dust devils, but we are not sure how frequently," says Phoenix Project Scientist Leslie Tamppari of NASA's Jet Propulsion Laboratory. "It could be they are rare and Phoenix got lucky. We'll keep looking for dust devils at the Phoenix site to see if they are common or not."
At least six different dust devils, ranging in diameter from about two metres to five metres, appear in the images captured this week, much smaller than dust devils that NASA's Mars Exploration Rover Spirit has photographed closer to the equator.
Click for animation. The Surface Stereo Imager caught this dust devil in action on 9 September. It was about 1 km away from the Lander when the first frame was taken, ,moving to about 1.7 km away two and a half minutes later. Image: NASA/JPL-Caltech/University of Arizona/Texas A&M University.
"It was a surprise to have a dust devil so visible that it stood with just the normal processing we do," says Mark Lemmon, lead scientist for the stereo camera that captured the dust devils in action. "Once we saw a couple that way, we did some additional processing and found there are dust devils in 12 of the images. 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."
As well as performing science experiments within the onboard laboratory, Phoenix also monitors the daily air pressure, and on the same day the camera saw dust devils, the pressure meter recorded a sharper dip than ever before seen. Phoenix also recorded wind speeds of at least five metres per second.
"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," says 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."
Phoenix scientists believe that the whirlwinds are getting stronger as the difference in day and nighttime temperatures increases. While daytime highs at the Phoenix site are still about minus 30 Celsius, the nighttime lows have been dropping steadily as summer in the northern hemisphere draws to a close, getting close to minus 90 Celsius.
The decline in daylight hours means that the project scientists must hurry to squeeze every last ounce of science out of the mission before Phoenix is unable to produce the electricity required to dig and perform experiments, which it does via its solar panels. With that in mind, a sample of icy soil from the Snow White trench has been selected for the final cell in the wet chemistry laboratory, and plans are being made to fill the remaining four of eight single-use ovens in the Thermal Evolved and Gas Analyser, without waiting for analysis of each sample to be completed before delivering the next.
"Now that the sun is not constantly above the horizon at our landing site we are generating less power every sol," says Phoenix Project Manager Barry Goldstein. "When we landed in late May, and through much of our mission, we generated about 3,500 watt-hours every sol. We are currently at about 2,500 watt-hours, and sinking daily.”
Sep 05 Phoenix's vapour quandary read more
Aug 26 Phoenix digs into extended mission... read more
Aug 06 Martian salts analysed for habitability... read more
Aug 01 Phoenix tastes water on Mars read more
Jul 29 Sticky situation for Phoenix read more
Jul 22 Phoenix in 24-hour monitoring assignment read more
Jul 17 Phoenix rasps frozen layer... read more
Jul 11 First success with Phoenix soil probe... read more
Jul 10 Phoenix struggling with icy payload read more
Jul 03 Next Phoenix bake could be last read more
Jun 30 Phoenix soil could support life read more
Jun 23 Frozen water confirmed on Mars read more
Jun 19 Bright chunks must have been ice read more
Jun 17 First results from Phoenix bakery read more
Jun 12 An oven full of sand read more
Jun 10 Clumpy Martian soil challenges Phoenix read more
Jun 06 Closest view ever of Mars sand read more
Jun 03 Phoenix scoops up Martian soil read more
Jun 02 Phoenix sees possible ice read more
May 30 Phoenix flexes robotic arm read more
May 28 HiRISE captures Phoenix descent read more
May 26 Spectacular new colour view of Mars read more
May 23 Phoenix prepares for Mars landing read more