Frost? - Sol 257

Caption NASA originale:"Frost can form on surfaces if enough water is present and the temperature is sufficiently low. On each of NASA's MER's, the calibration target for the PanCam provides a good place to look for such events. A thin frost was observed by Opportunity's PanCam on the Rover's 257th Sol (Oct. 13, 2004), just 11 minutes after sunrise (left image). The presence of the frost is most clearly seen on the post in the center of the target, particularly when compared with the unsegmented outer ring of the target, which is white. The post is normally black. For comparison, note the difference in appearance in the image on the right, taken about 3 hours later, after the frost had dissipated. Frost has not been observed at Spirit, where the amount of atmospheric water vapor is observed to be appreciably lower. Both images were taken through a filter centered at a wavelenght of 440 nnmts (blue)".