Mars has a number of striking geological features and one among them is the giant dome of layered ice and dust at its northern pole, which can be said to be similar to what we find here on Earth – ice sheets.
Just recently European Space Agency’s Mars Express sent across a comprehensive view of Mars’ unique north polar ice cap in the form of a mosaic created using images stitched together. The mosaic was generated from 32 individual orbit ‘strips’ captured between 2004 and 2010, and covers an area of around a million square kilometres and shows distinctive dark spiralling troughs on Mars’ north polar ice cap.
The ice cap is a permanent fixture, but in the winter season – as it is now in early 2017 – temperatures are cold enough for around 30 percent of the carbon dioxide in the planet’s atmosphere to precipitate onto the cap, adding a seasonal layer up to a metre thick. During the warmer summer months most of the carbon dioxide ice turns directly into gas and escapes into the atmosphere, leaving behind the water-ice layers.
Strong winds are thought to have played an important role in shaping the ice cap over time, blowing from the elevated centre towards its lower edges and twisted by the same Coriolis force that causes hurricanes to spiral on Earth.
One particularly prominent feature is a 500 kilometre-long, two kilometre-deep trench that almost cuts the cap in two. The plunging canyon, known as Chasma Boreale, is thought to be a relatively old feature, forming before the ice, dust spiral features, and seemingly growing deeper as new ice deposits built up around it.
Subsurface investigations by radar instruments onboard Mars Express and NASA’s Mars Reconnaissance Orbiter revealed that the ice cap is made up of many individual layers of ice and dust extending to a depth of around two kilometres. This presents a valuable record for the nature of how the planet’s climate has changed as its tilt and orbit varied over hundreds of thousands of years.
Data from High Resolution Imaging Science Experiment (HiRISE) on board NASA’s MRO has enabled scientists to digitally reconstruct the complex layers essentially creating virtual ice cores of the Martian ice sheet. Scientists have analyzed the differences in shape, steepness, and brightness of the icy layers exposed in these trough walls of the northern cap and found recurring characteristics in the virtual cores that had not been detected before.
Researchers believe that there is now solid observational evidence that the emplacement of the icy layers was influenced by orbital changes that occur every 50,000 to 120,000 years and cause periodic shifts in the planet’s climate.
To confirm their findings, the team ran simulations of ice and dust accumulation driven by changes in Mars’s orbit and tilt and found that the models produce layered patterns similar to those observed by HiRISE. The researchers noted that because Mars has larger orbital variations than Earth but lacks the complicating variables of life, an ocean, and a thick atmosphere, it provides an ideal model for studying how orbital shifts affect a planet’s climate and topography.