HiRISE Captures Stunning Images of Mars Avalanches in Action

Magnificent images of avalanches of ice and rock in the northern polar regions of Mars have been captured by NASA Mars Reconnaissance Orbiter’s (MRO) High Resolution Imaging Science Experiment (HiRISE). These images are not of landslides that have happened in the past, they are actual Mars avalanches happening at the moment of observation. This rare event will be of tremendous value to Mars scientists currently analysing the effects of seasons on the landscape and will provide information on the geological activity of the planet…

This event occurred along a scarp (a distinct cliff, with a steep runoff) around the North Polar Region where surface ice can be found in large quantities. The HiRISE instrument was being used to assess seasonal changes around the North Pole when four areas of activity were seen along the scarp. HiRISE was witness to something more familiar on Earth than on Mars: avalanches.

This particular scarp is a high cliff over 700 m (2300 ft) tall and slopes at over 60 degrees. A mixture of ice, rock and dust can be seen, frozen in time, as it is plummeting down the slope, ejecting a plume of dust as the debris begins to settle on the gentle slope at the bottom of the cliff. The ejected cloud is approximately 180 meters across and extends about 190 meters beyond the base of the cliff. It is worth noting that the clouds are large 3D structures reaching into the Martian atmosphere and not 2D patterns on the surface (shadows from the plume can be seen to the lower left of the clouds of dust).

The Martian landscape does not change very much over millions of years. Unlike the Earth, Mars does not have a thick, eroding atmosphere blasting away at the surface features. The lack of water also reduces these erosion effects. Mars also has very little geological activity as core reactions are thought to have slowed or even stopped – there is therefore very little tectonic movement, no major earthquakes and no evidence for present volcanic activity.

So what caused these avalanches? HiRISE scientists have some ideas:

• Disappearance of carbon dioxide frost, dislodging rocks.
• Expansion and contraction of ice due to seasonal temperature differences.
• Small Mars-quakes.
• A nearby meteorite impact.
• Vibrations from other avalanches causing other avalanches along the scarp

It seems most likely that the trigger may be down to seasonal changes. As the North Polar Region heats up (progressing toward summer), solid carbon dioxide (“dry ice”) may be subliming, weakening rocks around the edge of the cliff. The same could be said for the thermal expansion and contraction of water ice as the seasonal air temperature becomes warmer or cooler.

Whatever the cause, we are very lucky to have captured this event, the science collected from these observations will be critical to understanding how the Martian landscape can change very rapidly. The HiRISE instrument continues to return the most magnificently detailed images of the Red Planets surface, these observations of Mars avalanches will certainly go into the Mars Reconnaissance Orbiter’s Hall of Fame…

Source: HiRISE Project Site