China’s Zhurong Mars rover has found evidence of a dramatic shift in the Martian climate 400,000 years ago, in the form of dark hills set atop bright sand dunes that ripple across the sands of Utopia Planitia, which the rover is exploring.
Scientists led by Li Chunlai of the National Astronomical Observatories of the Chinese Academy of Sciences used the rover’s instruments, along with high-resolution observations from China. Tianwen-1 Mars, to take a closer look at the large sand dunes near Zhurong Place Landed May 2021.
The dune crescent shape has eroded over hundreds of thousands of years, with long, dark ridges called transverse aeolian rims (TARs), which formed over dune fields, but apparently at a different angle than those of windswept dunes. CARs have been noticed everywhere Mars at lower mid-latitudes, but global atmospheric circulation models describing wind direction on the Red Planet have been unable to explain what the features might be — until now.
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Zhurong’s investigation of the dunes found that their crescent-shaped bodies are made of brighter material beneath the darker material that makes up the TARs. From orbit, Tianwen-1 observed 2,262 bright dunes across Mars, and based on the number of craters that collided over the dunes, the research team estimates they formed between 2.1 million and 400,000 years ago. This means that dark tar trains must have formed over it within the past 400,000 years.
These dates coincide with the beginning and end of the last major ice age on Mars. For TARs to form at a different angle than the dunes would mean that wind direction in lower mid-latitudes would have to change with the end of the Ice Age.
The ice age started and ended due to changes in the angle at which Mars rotates Milankovitch courses. These cycles involve a periodic wandering of a planet’s axis of rotation relative to the plane of its orbit, due to the combined effects of a planet’s gravity the sunAnd Jupiter and other planets, as well as the shape and trajectory of the planet’s orbit.
Earth and Mars both go through these cycles, which correspond to climate shifts. In the case of Mars, its rotation angle (referred to as its tilt) varied between 15° and 35° between 2.1 million and 400,000 years ago, wreaking havoc on its climate. Today, Mars’ tilt is about 25 degrees.
It is somewhat surprising that there was an ice age on Mars Not quite the same as on Earth. Typically, Martian ice ages see warmer temperatures at the poles, and movement of water vapor and dust toward mid-latitudes, where they are deposited. During the last ice age, this water and dust formed a meter-thick layer that still lingers below the surface at selected locations below 60° latitude, and almost everywhere above 60°.
The current geological age on Mars is known as the Amazon Age, which sometimes began between 3.55 and 1.88 billion years ago and is determined by the number of impacts during that period.
“Understanding the climate of the Amazon is essential to explain the current Martian landscape, volatiles reservoirs and atmospheric state, and to relate these current observations and energetic processes to ancient climate models of Mars,” Lee he said in a statement. “Observing the current climate of Mars can help improve physical models of Martian climate and landscape evolution, and even form new models.”
Meanwhile, the Zhurong rover has gone into hibernation during the long northern Martian winter. It has not been reactivated yetHer fate remains uncertain.
The results are published July 5 in the journal nature.
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