By Chris Skeldon 
The Chinese rover Zhurong has found evidence of abrupt climate change on Mars 400,000 years ago. They are represented as dark hills atop light dunes in the sands of Utopia Planitia, which the rover explored.
Transversal atmospheric ridge (TAR) image of a dune field on Mars near the Certis Principal Plateau, taken by NASA’s Mars Reconnaissance Orbiter. Image credit: 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 along with high-resolution images from the Tianwen-1 Martian Orbiter in China to get a closer look at a large sand dune nearby. Local landing of the Zhurong rover in May 2021.
The crescent-shaped dunes eroded over hundreds of thousands of years, and long, dark ridges known as Transverse Aeolian Ridges (TARs) formed over the dune fields. It is located at a different angle from the tops of the dunes, which were formed by the wind. CARs have been observed on Mars at low mid-latitudes, but global atmospheric circulation models describing wind direction on Mars have so far failed to explain how atmospheric transverse ridges form.
How the winds on Mars changed as the end of the Ice Age approached, forming tall hills at a different angle than the dunes. Image source: não.cas.cn
Exploring the dunes, the Jurong rover discovered that their growing bodies consist of lighter material beneath the darker material that makes up the TAR. From orbit, Tianwen-1 observed 2,262 bright dunes on Mars, and based on the number of craters that formed above the dunes, the research team suggests they formed between 2.1 million and 400,000 years ago. This means that the dark TAR must have formed over it within the past 400,000 years.
These dates coincide with the beginning and end of the last great ice age on Mars. The fact that the TAR forms at a different angle than the dunes means that wind direction at low mid-latitudes must have changed with the end of the Ice Age.
The Ice Age began and ended due to changes in the angle of rotation of Mars due to the Milankovitch cycles. These cycles are associated with a periodic shift of the axis of rotation of the planet relative to the plane of its orbit, caused by the combined effect of the gravitational attraction of the Sun, Jupiter and other planets, as well as the shape and trajectory of the planet. orbit.
Both Earth and Mars go through these cycles, which correspond to climate change. In the case of Mars, its rotation angle (called tilt) varied from 15 to 35 degrees between 2.1 million and 400,000 years ago, wreaking havoc on its climate. The tilt of Mars today is about 25 degrees.
Surprisingly, the ice age on Mars did not happen in the same way as it did on Earth. Martian ice ages are usually characterized by the warming of the poles and the movement of water vapor and dust toward mid-latitudes, where they settle. During the last ice age, this water and dust formed a layer several meters thick, which remains below the surface in some places below 60° latitude and almost everywhere above 60°.
The current geological epoch on Mars, known as the Amazon 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 cool conditions, generally similar to those on Mars today.
“Understanding the climate of the Amazonian era is essential to explaining the modern Martian landscape, volatiles reservoirs, and atmospheric conditions, and to relate these modern observations and energetic processes to ancient Martian climate models. Observations of the current climate on Mars,” Li Chunlai of the National Astronomical Observatory of the Chinese Academy of Sciences said in a statement. It could help improve physical models of the evolution of Mars’ climate and landscape, and even form new ones.
Meanwhile, the Jurong rover has been idle during the long Martian northern winter. As of now, it has not yet been activated and its fate remains uncertain.