Deuteronilus Mensae is a region on Mars 937 km across and centered at . It covers 344° -325° West and 40°-48° North.[1] Deuteronilus region lies just to the north of Arabia Terra and is included in the Ismenius Lacus quadrangle. It is along the dichotomy boundary, that is between the old, heavily cratered southern highlands and the low plains of the northern hemisphere. The region contains flat-topped knobby terrain that may have been formed by glaciers at some time in the past. Deuteronilus Mensae is to the immediate west of Protonilus Mensae and Ismeniae Fossae.[2] [3] Glaciers persist in the region in modern times, with at least one glacier estimated to have formed as recently as 100,000 to 10,000 years ago.[4] Recent evidence from the radar on the Mars Reconnaissance Orbiter has shown that parts of Deuteronilus Mensae do indeed contain ice.[5][6]
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It is now widely believed that ice accumulated in many area of Mars, including Deuteronilus Mensae, when planet's orbital tilt was much different than it is now (the axis of Mars has considerable "wobble," meaning its angle changes over time).[7] [8] [9] A few million years ago, the tilt of the axis of Mars was 45 degrees instead of its present 25 degrees. Its’ tilt, also called obliquity, varies greatly because its two tiny moons cannot stabilize it, like our relatively large moon does to the Earth. During periods of high tilt, the ice caps at the poles disappear, the atmosphere thickens, and the moisture in the atmosphere goes up. These conditions cause snow and frost to appear on the surface. Some of the moisture would have coated dust grains until the grains would be too heavy to be held up in the atmosphere; they would then fall and accumulate on the surface. Just plain snow would have also added to the mix. Ice on the surface of Mars today would immediately sublimate (or change directly into the gas phase). The rocky debris and dust covering ice is likely what has allowed it to survive below the surface for millions of years.