Published by the Students of Johns Hopkins since 1896
September 21, 2020

Mars ice caps decode planet’s past

By Mo-Yu Zhou | September 13, 2012

In order to glean information about Earth’s climate history, scientists can analyze ice cores from Greenland and Antarctica’s ice caps. Similarly, Mars’ past climate can be determined by examining its ice caps. Using this technique, researchers from the Niels Bohr Institute at the University of Copenhagen have put together the first dated account of climate history for Mars. Their findings show that the variations in Mars’ climate are linked to solar insolation, which is a measure of solar radiation energy.

Mars’ poles feature ice caps that are kilometers thick. These caps are composed of ice and dust, and the layers produced by the accumulation of the ice and dust reflect past climate patterns. The layers have been known for decades— since the first satellite images came back from Mars— and provide us with clues about Mars’ wildly fluctuating climate over time.

Solar insolation has seen dramatic variations, caused largely by Mars’ obliquity, or the tilt of its rotational axis. This has been associated with extreme variations in Mars’ climate, and it is believed that the layers of ice caps could provide some clue as to the link between Mars’ climate and solar insolation.

For years, scientists have tried to link the formation of the layers of ice and dust with the solar insolation on Mars by looking for signs of visible periodic sequences in the upper 500 meters of the ice caps. However, it has proven difficult to find a correlation between the layers and the variations in insolation by looking for periodic sequences, even though the two may be connected.

However, the researchers at the Centre for Ice and Climate at the Niels Bohr Institute decided to try a different approach. Instead of looking for periodic sequences in the visible layers of the ice caps, researchers developed a model describing how layers are formed based on fundamental physical processes. In this way, they managed to find a correlation between solar insolation and the accumulation of ice and dust.

The layers of ice and dust can be formed as a result of two different processes. The first involves high obliquity, the rotational axis tilting down during the summer, which results in increased evaporation of ice. The second process involves variations in the axial tilt, which produces changes in dust accumulation.

Although the model is simple, it is viable and practical as a tool for examining the connection between the formation of ice and dust layers and the variations in the climate of Mars. Indeed, the model proved to be consistent with empirical observations. Precise measurements of the structure of the ice caps from high-resolution satellite images of Mars’ north pole were compared against the model, which was able to faithfully reproduce the complexity of the layers.

The upper 500 meters of the ice caps, which is the area that the model examines, correspond to about one million years of ice and dust accumulation. In those years, the average accumulation rate of ice and dust was about 0.55 mm per year. The model was successful in linking individual layers to maxima in solar insolation, thereby producing a dated history of Mars’ north pole over a million years.

Although the model is solely based on the upper 500 meters of the ice caps on Mars’s north pole, preliminary follow-up studies seem to confirm the model for all of the ice caps. Thus, the model produced by these researchers is highly promising in providing a definitive description of how ice and dust have accumulated on Mars for millions of years.

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