S ANCIENT IMPACT Some landscapes on Mars seem to be all about texture. The bumpy-looking surface surrounding this crater vaguely resembles reptilian skin. The crater lies west of Olympia Mensae in the Red Planet's high northern plains. (A mensa is a flat-topped prominence with cliffy edges, like a mesa on Earth.) S MARTIAN INK-BLOT TEST We recognize the dunes and ripples, but what are the black blotches? They toy with the mind for an explanation of shape, pattern, consistency. What we're looking at is the result of sublimation of carbon dioxide frost in the late Martian winter. This jump from solid to vapor is complicated, resulting in the multifarious forms and patterns we see here, including grayish halos around some of the larger blotches. SHADOWED GULLIES Deeply incised walls like this one characterize many craters in the Martian mid-latitudes. Of particular interest to scientists are seasonal changes, such as the color-enhanced blue deposits seen here in Gasa Crater. Captured in the early spring, the deposits are carbon dioxide frost that appeared the preceding winter. sk yandtelescope.org * OCTOBER 2 02 0 19http://www.skyandtelescope.org