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09.07.2023 21:27, Dmitry Fedorov
China’s Zhurong rover has found evidence of dramatic climate change on Mars 400,000 years ago. They are represented as dark ridges located on top of light dunes in the sands of the Utopia Plain (Utopia Planitia), which the rover explored.
Image of transverse aeolian ridges (TAR) in a dune field on Mars near the Syrtis Major Plateau, taken by NASA’s Mars Reconnaissance Orbiter. Image Source: NASA/JPL–Caltech/University of Arizona
Scientists led by Li Chunlai of the National Astronomical Observatory of the Chinese Academy of Sciences (NAOC) used the rover’s instruments in combination with high-resolution imagery from China’s Tianwen-1 Martian Orbiter to take a closer look at large sand dunes. near the landing site of the Zhurong rover in May 2021.
The crescent-shaped dunes have been eroded over hundreds of thousands of years, and long, dark ridges known as transverse aeolian ridges (TARs) have formed at the top of the dune fields. They are located at a different angle than the ridges of the dunes formed by the action of the wind. TARs have been observed throughout Mars in the lower mid-latitudes, but global atmospheric circulation models describing the direction of the winds on Mars have so far been unable to explain how transverse aeolian ridges could form.
How the winds on Mars changed as the Ice Age came to an end, forming long ridges at a different angle to the dunes. Image source: nao.cas.cn
While exploring the dunes, the Zhurong rover found that their crescent bodies are composed of lighter material underneath the darker material that forms the TAR. From orbit, Tianwen-1 observed 2,262 bright dunes across Mars, and judging by the number of dune-top craters, the research team suggests they formed between 2.1 million and 400,000 years ago. This means that dark TARs must have formed on top of them within the last 400,000 years.
These dates coincide with the beginning and end of the last major ice age on Mars. That the TAR formed at a different angle to the dunes means that the wind direction in the lower mid-latitudes must have changed with the end of the ice age.
The ice age began and ended due to changes in the angle at which Mars rotates, caused by Milankovitch cycles. These cycles are associated with a periodic displacement of the planet’s axis of rotation relative to the plane of its orbit, caused by the combined effect of the gravity of the Sun, Jupiter and other planets, as well as the shape and precession of the planet’s orbit.
Both Earth and Mars experience these cycles, which correspond to climate shifts. In the case of Mars, its angle of rotation (called inclination) varied from 15 to 35 degrees between 2.1 million and 400,000 years ago, wreaking havoc on its climate. Today, the inclination of Mars is about 25 degrees.
Somewhat surprisingly, the ice age on Mars did not proceed quite the same way as on Earth. Typically, Martian ice ages are characterized by warming at the poles and the movement of water vapor and dust to the middle latitudes, where they settle. During the last ice age, this water and dust formed a layer several meters thick, which still remains below the surface in some places below 60 degrees latitude and almost everywhere above 60 degrees.
The current geological epoch on Mars, known as the Amazonian epoch, began between 3.55 and 1.88 billion years ago. During this period, collisions with meteorites and asteroids occurred on Mars, but their speed was low. This period is characterized by cold conditions, generally similar to those that exist on Mars today.
«Understanding the climate of the Amazonian era is necessary to explain the modern Martian landscape, volatile matter reservoirs, and atmospheric conditions, and to relate these modern observations and active processes to models of the ancient Martian climate. Observations of the current climate of Mars can help refine physical models for the evolution of the Martian climate and landscape, and even form new paradigms.” Li Chunlai of the National Astronomical Observatory of the Chinese Academy of Sciences said in a statement.
Meanwhile, the Jurong rover went dormant during the long northern Martian winter. As of now, it has not yet been activated, and its fate remains uncertain.
