China’s Zhurong Mars rover has found evidence of a dramatic shift in Mars’ climate 400,000 years ago, in the shape of dark ridges laid on top of brilliant dunes that ripple across the sands of Utopia Planitia, which the rover is exploring.
Scientists led by Li Chunlai from the National Astronomical Observatories of the Chinese Academy of Sciences used the rover’s instruments, coupled with high-resolution observations from China’s Tianwen-1 Mars orbiter, to take a better take a look at large sand dunes near where Zhurong landed in May 2021.
The crescent shape of the dunes has been eroded over a whole bunch of thousand years, with long dark ridges, called transverse aeolian ridges (TARs), forming on top of the dune fields, but apparently at a unique angle than that of the wind-blown dunes. TARs have been observed all across Mars at lower mid-latitudes, but global atmospheric circulation models that describe the direction of the winds on the Red Planet have been unable to clarify how the features could have formed — until now.
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Zhurong’s investigation of the dunes found that their crescent-shaped bodies are product of brighter material underneath the darker material that forms the TARs. From orbit, Tianwen-1 observed 2,262 brilliant dunes across Mars, and based on the variety of craters which have impacted on top of the dunes, the research team estimates that they formed between 2.1 million and 400,000 years ago. Which means the dark TARs should have formed on top of them inside the past 400,000 years.
These dates coincide with the beginning and end of Mars’ last major ice age. For the TARs to have formed at a unique angle to the dunes implies that the wind direction within the lower mid-latitudes should have modified with the top of the ice age.
The ice age began and ended due to changes within the angle at which Mars spins, caused by Milankovitch cycles. These cycles involve a periodic wandering of a planet’s rotational axis relative to the plane of its orbit, brought on by the combined effects of the gravity of the sun, Jupiter and the opposite planets, in addition to the form and precession of the planet’s orbit.
Each Earth and Mars experience these cycles, which correspond to climatic shifts. Within the case of Mars, its angle of rotation (known as its obliquity) varied between 15 degrees and 35 degrees between 2.1 million and 400,000 years ago, playing havoc with its climate. Today, Mars’ obliquity is about 25 degrees.
Somewhat surprisingly, an ice age on Mars is not quite the identical as on Earth. Typically, Martian ice ages see warmer temperatures on the poles, and movement of water vapor and dirt towards the mid-latitudes, where they’re deposited. In the course of the last ice age, this water and dirt formed a meters-thick layer that also stays beneath the surface in chosen locations below 60 degrees latitude, and almost in all places above 60 degrees.
The present geological era on Mars is often known as the Amazonian epoch, which began sometimes between 3.55 and 1.88 billion years ago and is defined by the variety of impacts over that point.
“Understanding the Amazonian climate is important to clarify the present Martian landscape, volatile matter reservoirs and atmospheric state, and to relate these current observations and energetic processes to models of the traditional climate of Mars,” Li said in an announcement. “Observations of the present climate of Mars may help refine physical models of Martian climate and landscape evolution, and even form recent paradigms.”
Meanwhile, the Zhurong rover entered hibernation during Mars’ long northern winter. It’s yet to reactivate, and its fate stays uncertain.
The findings were published onJuly 5 within the journal Nature.