On the mechanisms of possible periodic redistribution of water ice between the polar caps of Mars

Abstract

At the beginning of the 21st century, the presence of a significant amount of water ice was confirmed in the Arctic Cap. A little later, the instruments of the "Mars Express" orbiter were also able to register considerable deposits of water ice around the South Pole. And a layer of "dry" ice with a thickness of 2 to 7 mm was found above the water ice. Total sediments in the South Polar Cap turned out to be significantly smaller than in the North. Observations with the help of a gamma spectrometer made it possible to detect a large amount of hydrogen contained under the surface of Mars at significant distances from the polar caps, and even at the planet's equator. This hydrogen is part of water ice, which in such places is protected from sublimation by a soil made of insulating rock, dust, and rock fragments. During summer dust storms, significant amounts of dust are raised as a result of the rapid seasonal movement of carbon dioxide and water vapor; after a certain time, this dust settles from the atmosphere. This leads to a seasonal accumulation of dust in layered deposits in both polar and subpolar regions. When the seasons change on the planet, as a result of the significant eccentricity of the orbit of Mars, there is a significant asymmetry in the changes in the inflow of solar energy to the opposite hemispheres. The differences between aphelion and perihelion reach 40%. For this reason, when the planet is in aphelion, the summer in the Northern Hemisphere is longer and colder than in the Southern. Due to such a difference in seasonal characteristics between the southern and northern hemispheres, a kind of seasonal "pump" in a relatively short period of time can completely transfer water to the polar cap in the hemisphere in which summer falls on passing through the aphelion of the orbit. Modeling of present-day climate processes on Mars indicates that water ice deposits should be cyclically redistributed between the south and north polar regions of Mars for about 21,000 years. The rotation axis of Mars in Milankovitch cycles could change its inclination many times. The period of such changes is close to 105 years. Therefore, the asymmetry described in the paper is young, which may lead to a change in sign. Therefore, it is quite possible that during the history of Mars, the polar caps have repeatedly changed places.