The planet Mars undergoes dramatic changes in its axial tilt on a timescale of hundreds of thousands of years. This is unlike Earth, whose axial tilt is stabilised by the presence of our Moon. As a result, Mars experiences significant changes in climate. This illustration shows cutaways through the crust of Mars during the Hesperian Period (3700-3100 million years ago), when Mars was cold but mostly dry and volcanic. At its coldest (right), much of the surface was blanketed in ice or snow. However, as the climate warmed (left), erupting volcanoes were able to melt the ices both on the surface and just below it, leading to large-scale catastrophic flooding which likely created the Martian outflow channels.The subsurface aquifers remain present during both extremes.