Each Martian spring, the northern polar cap undergoes warming by the sun. The ices sublimate into the thin atmosphere and leave behind dust and rocks. This image shows the edge of the ice cap at the upper right and a dust cloud from an avalanche of this dust and rock debris toward the lower left. The avalanche had just occurred when the image was recorded.
The 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). MRO launched in 2005. The mission timeline originally called for an end in 2009. But, the mission is now designated as ongoing.
The rare events are of value to Mars scientists analyzing the effects of seasons on the landscape and provide information on the geological activity of the planet. These avalanches occurred along a steep scarp, or cliff, around the North Polar Region. Surface ice can be found in large quantities. The HiRISE instrument was being used to assess seasonal changes around the North Pole when areas of activity were seen along the scarp. This scarp is a high cliff over 700 m tall and slopes at over 60 degrees. It is the pinkish brown region extending from the white ices at the top right part of this image. A mixture of ice, rock and dust slid down the slope and ejected a plume of dust at the bottom of the cliff. The dust cloud is about 180 meters across and reaches about 190 meters beyond the base of the cliff. The dust clouds are large 3D structures reaching into the Martian atmosphere.
This is a video of the north polar cap. Courtesy of European Space Agency.
The next two images show avalanches caught in the act along the scarp of the ice cap by the same pass of the MRO spacecraft. Capturing two at once indicated the frequency of these springtime events.
The Martian landscape does not change very much. Unlike the Earth, it doesn’t have a thick atmosphere eroding the surface. It lacks the water we have on Earth to cause large erosion effects. Mars also has very little geological activity and tectonic movement. No major earthquakes or present volcanic activity has been detected by the craft which are monitoring and studying Mars.
So why are there avalanches? HiRISE scientists have some ideas:
- Disappearance of carbon dioxide frost dislodges rocks
- Expansion and contraction of ice
- Small Mars-quakes
- Nearby meteorite impact
- Vibrations from other avalanches
Seasonal change seems the most likely trigger. As the North Polar Region warms, solid carbon dioxide, “dry ice”, sublimes. It goes from the solid frozen state to the vapor state without melting. This loosens the larger rocks at the upper edge of the cliff. Thermal expansion and contraction of water ice can do the same thing and loosen rocks here on Earth. Each of the recent spring seasons on Mars, the spacecraft has captured avalanches in action.
Some of the avalanche images came from the PDS image release of February 2012. This release covers MRO orbits 25,000 to 25,399. One of my favorite parts of this image release is the anaglyph set. These are images viewed with red and blue colored filters over your eyes to give the effect of depth. (Red over left eye. Blue over right eye.) The PDS is the curator for images of planetary missions at NASA.
The Imaging Node of the Planetary Data System is the curator of NASA’s primary digital image collections from past, present and future planetary missions. The node provides to the NASA planetary science community the digital image archives, necessary ancillary data sets, software tools, and technical expertise necessary to fully utilize the vast collection of digital planetary imagery.
The 2013 PDS image release is just out. Here is an image from that set. It is along the scarp of the ice cap. The higher elevation ice is on the right. The lower elevation Martian surface on the left. The boundary shows layering in this overhead view. But, no avalanches show in this image. Click the image for a large detailed version.