Secrets of the Red Planet: Mystery of polar ice and Mars' atmosphere solved by scientists

The new model developed by scientists is trying to explain the peculiar nature of water and ice deposits at the South Pole of Mars, which seem to contain as much CO2 as the entire atmosphere of the planet.

Polar ice and Mars.

Researchers from the California Institute of Technology (Caltech), the University of Colorado and NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, have developed a new model that explores the relationship between the Martian atmosphere and its ice layers, reports

Water and ice deposits at the South Pole of Mars.

According to thr reports, the team tried to confirm the theory presented in 1966 by two Caltech scientists, who suggested that the thin carbon dioxide atmosphere on Mars, first discovered by the spacecraft Mariner IV, can be explained by the existence on the planet of long-term stable polar CO2 ics, which controls the planet's atmospheric pressure.

The new model investigates the existence of a layered deposit of ice water and CO2 ice at Mars' south pole, which seems to contain amount of CO2 that is equal to amount of CO2 in the planet's atmosphere today.

Generally speaking when you run a model, you don't expect the results to match so closely to what you observe 

But the thickness of the layers defined by the model is perfectly consistent with the radar measurements of the orbiting satellites, said Dr. Peter Bühler, JPL researcher and the author of the recent study.

The researchers suspect that the sediment was formed as a result of the oscillations of Mars' rotational axis over the past 510,000 years, resulting in different amounts of sunlight at the Pole.

The Caltech research on Mars atmosphere 

In 1966, two Caltech scientists investigated the effects of the thin Martian atmosphere of carbon dioxide (CO2), first detected by the JPL spacecraft built and launched by NASA Mariner IV. 

The Caltech researchers developed a theory that Mars' atmosphere could have a long-lasting stable deposit of polar ice (CO2), which would control global atmospheric pressure.

  • New research by Caltech suggests that the theory developed by physicist Robert B. Leighton (BS '41, MS '44, Ph.D. '47) and planetary scientist Bruce C. Murray may be true.

Carbon dioxide accounts for more than 95% of the atmosphere of Mars, whose surface pressure is only 0.6% of the earth's pressure. 

One of the predictions of Leighton and Murray's theory, which has a huge impact on climate change on Mars, is that the amount of atmospheric pressure will change if the planet will oscillate around its axis during its orbit around the Sun and the poles will be more or less exposed to sunlight. 

Direct radiation of the sun on the CO-2 deposited ice on the poles leads to its sublimation (direct transfer of material from solid to gaseous state).

Leighton and Murray predicted that air pressure, when solar radiation changes in cycles of tens of thousands of years, can vary from a quarter of today's Martian atmosphere to twice the air pressure.

The new model by Dr. Peter Bühler of JPL, at NASA, and colleagues at Caltech, JPL and Colorado State University are important proof of this. This model was described in an article published in Nature Astronomy.

The group studied the existence of a mysterious feature at the South Pole of Mars: massive deposition of carbon dioxide ice and water ice in alternating layers, such as dough layers stretching to a depth of 1 kilometre, with a thin layer of carbon dioxide ice on top. 

The deposit of the layer contains the same amount of CO 2 as in today's Martian atmosphere.

  • Theoretically such a layer shouldn't be possible because water ice is more thermally stable than CO 2. 

CO2 ice, according to scientists, quickly destabilizes if it is submerged under water ice. 

However, the new model developed by Bühler and his colleagues shows that deposition can be caused by a combination of three factors:

1. change in tilt of the planet's rotational axis.
2. different ways in which sunlight is reflected by ice and water.
3. an increase in atmospheric pressure.

According to Bühler, when researchers run a model, they don't expect the results to match what they observe so closely. However, the thickness of the layer defined by the model corresponds very well to the radar measurements of the orbiting satellites.

The researchers suspect that the deposit was created in the following manner: as Mars' axis of rotation has changed over the past 510,000 years, the planet's South Pole was exposed to different amounts of sunlight, allowing ice to form from carbon dioxide when the poles received less sunlight, and caused it to rise when sunlight was more abundant. 

When the CO 2 ice deposited at Mars' poles is exposed to direct sunlight sublimation occurs - the process of the transition of a material from a solid to its gas state.

CO 2 sublimation, in turn, increases atmospheric pressure on Mars and leads to the development of CO 2 ice layers. When sunlight is scarce once again, a new layer of CO2 ice forms over the water layer and the cycle repeats itself.

As the intensity of sublimation episodes has generally decreased, part of the CO 2 ice layer remains between the water layers, alternating with CO 2 and water ice. 

The deepest and therefore, oldest layer of CO 2 was formed 510,000 years ago, after the last period of extreme polar solar radiation, when all CO 2 was sublimated in the atmosphere.

Our definition of the history of major pressure changes on Mars is crucial to the understanding of Martian climate evolution, including the history of stability and the possibility of liquid water near the surface of Mars, says Bühler. 

This research work was part of Bühler's thesis at Caltech. He continued his research in his current postgraduate role at NASA's JPL. It was co-authored by his former advisors Andrew Ingersoll and Bethany Ehlmann, professors of Planetary Science at Caltech.

  • For more information about the mars atmosphere study: P. B. Buhler et al. Coevolution of Mars's atmosphere and massive south polar CO2 ice deposit, Nature Astronomy (2019). DOI: 10.1038/s41550-019-0976-8