What are they? I’ve seen some odd photos from the Martian surface, but when I first saw this image, the pinks, blues and yellow smudges looked… alien. The surprise probably comes from the fact that we are so used to the rusty red pictures to come from the various rovers, landers and satellites, that any colour not a variation of red comes as a shock.
Although it looks odd, there is in fact a sensible answer to these ghostly splodges on the horizon. This photo was snapped by Mars Expedition Rover (MER) Spirit back on sol 1919 of the MER mission on May 27th, 2009.
Using its panoramic camera (Pancam), Spirit performed a number of exposures, each one using a different colour filter. With some luck during the photography session of the Martian landscape, a dust devil (a mini whirlwind) meandered through the Pancam’s field of view. In each frame taken with different filters, the only feature moving would have been the swirling dust, so that’s why it appears as a different hue than the surrounding landscape.
Dust devils occur on both Mars and on Earth when solar energy heats the surface, resulting in a layer of warm air just above the surface. Since the warmed air is less dense than the cooler atmosphere above it, it rises, making a swirling thermal plume that picks up the fine dust from the surface and carries it up into the atmosphere. This plume of dust moves with the local wind. — NASA/JPL
Dust devils have provided some unexpected fun for the rovers, often tuning up unannounced. These make for interesting observations of local weather conditions, but they also provide an essential mini-undusting service for the wheeled robot’s solar panels.
And now they’ve been pictured in technicolour. How nice.