National Aeronautics and Space Administration researchers say an image captured by lander's robotic arm camera Sept. 1 shows growth of the clumps compared with what was present when a similar image was taken about three months earlier.

The NASA science team said it has discussed various possible explanations for the clumps. "One suggestion is that they may have started from a splash of mud if Phoenix's descent engines melted icy soil during the landing," the space agency said in a statement. "Another is that specks of salt may have landed on the strut and began attracting atmospheric moisture that freezes and accumulates."

The scientists note the clumps are concentrated on the north side of the strut that's usually in the shade, so the accumulation could be a consequence of the fact that condensation favors colder surfaces.

The Phoenix Mission is led by the University of Arizona-Tucson, on behalf of NASA. The project is managed by the space agency's Jet Propulsion Laboratory in Pasadena, Calif.