TES discovered why the "Mountains of Mitchel" (elongated feature, arrow) remain bright well into local spring. The "mountains," a misnomer that dates from the 19th century, are actually a heavily cratered area covered and uncovered each year by the southern seasonal polar cap. TES found the area remains cold and bright longer than other comparable areas because it is covered with unusually small grains of carbon-dioxide frost that persist longer. NASA/JPL/Arizona State University