Models of the stability of ground ice as a function of obliquity. The different panels show stability as a function of latitude and longitude for different obliquities, Theta. In the shaded areas ice is unstable at all depths. Contour lines in the unshaded areas show depths below which ice is stable. At present obliquity (panel b), ice is unstable at all depths at latitudes less than about 50 degrees. At lower obliquities the stability boundary moves slightly poleward. At higher obliquities the stability relations change dramatically such that at obliquities higher than 30 degrees ground ice is stable at shallow depths everywhere on the planet. (Adapted from Mellon and Jakosky, 1995. Courtesy of M. Mellon, NASA/Ames.)