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CUHK-led study reveals why Mercury’s young plains have the most “wrinkles”
Ongoing mantle activity continues to shape the planet’s surface
A research team led by The Chinese University of Hong Kong (CUHK) has uncovered new evidence that Mercury’s interior remained geologically active far longer than previously believed. Published in the prestigious international scientific journal Nature Communications, the study reveals that the relatively young plains near Mercury’s north pole exhibit more pronounced crustal compression and deformation than older regions, caused by an upwelling of hot rock from the deep mantle once occurred beneath the area. This challenges the long-standing theory that Mercury’s landscape was shaped dominantly by the planet’s cooling and contraction.
Mapping Mercury’s surface reveals anomalous tectonic deformation
Mercury is the smallest planet in the Solar System and the closest to the Sun. The evolution of Mercury’s landscape shares similarities with other terrestrial planets: as its hot interior slowly cooled over time, the whole planet contracted, causing its rocky outer shell to buckle into long cliffs and ridges – much like the skin of a drying apple.
The study focused on the Northern Smooth Plains, a vast volcanic plain near Mercury’s north pole that covers about 7% of the planet’s surface. Formed roughly 3.7 billion years ago, it is geologically young by Mercury’s standards. Under existing theories, most of the planet’s shrinking had already occurred, meaning this newer surface should have experienced less contractional deformation. The CUHK-led team mapped cliffs and ridges across the whole planet and measured the degree of crustal compression. Surprisingly, the results were the opposite of what they expected: this young plain turned out to be the most heavily wrinkled region on Mercury, indicating that cooling-driven contraction alone cannot fully explain the formation of the Northern Smooth Plains.
Mantle upwelling identified as another key driver of surface evolution
To investigate the cause of this anomaly, the team combined measurements of Mercury’s gravity and surface height with computer simulations of its interior. The results indicate that regional mantle activity can continue to shape Mercury’s surface morphology.
At the centre of the plain sits a broad, gentle bulge called the Northern Rise, which the study attributes to a plume of hot, buoyant rock that rose from about 350 km below the surface. Unable to breach the planet’s rigid outer shell, this rising rock spread out sideways beneath the crust, forming a flat layer roughly 730 km wide. That layer pushed up the centre of the plain and stretched it slightly, while pinching and wrinkling the surrounding plains.
Even after the hot rock cooled and the bulge began to sag, the compression did not stop. The slopes and residual stresses left behind continued to fracture the surface over a very long time, explaining why some cliffs and cracks in this region look surprisingly young and fresh.
“The damage forms a clear bull’s‑eye around the Northern Rise,” said Professor Zhan Yan, the study’s corresponding author and Ng Yin Ying Assistant Professor of Geophysics at CUHK’s Department of Earth and Environmental Sciences. “That pattern points to a heat source deep below, and it changes how we read Mercury’s cliffs and ridges.”
“Mercury is often written off as geologically dead,” said Dr Xie Jingchun, the study’s first author and a postdoctoral fellow at CUHK’s Department of Earth and Environmental Sciences. “We show that deep inside, something kept working on the surface long after the planet’s main thermal evolution had faded – much like a footprint that keeps pressing into the ground after the foot has already lifted.”
Broad implications for terrestrial planetary science
The team believes this study provides a new framework for understanding tectonic features on Mercury that can be applied to other celestial bodies. Similar deep-seated upwellings are suspected on Mars and Venus, but previous studies have rarely linked them so clearly to surface cracks and cliffs. By integrating surface mapping with interior dynamic modelling, this research demonstrates how rocky planets cool and shrink, while localised deep-mantle heat sources can rejuvenate geological activity for billions of years.
“It is striking that a process starting from such depths can leave such a neat pattern at the surface,” said co‑author Dr Zhang Jian of The University of Hong Kong. “It shows that the interior and the surface of Mercury stayed connected for far longer than we previously assumed.”
The full text of the research paper in Nature Communications can be accessed here: https://www.nature.com/articles/s41467-026-74975-0
About the study
This research was supported by the Hong Kong Research Grants Council, the National Natural Science Foundation of China and the Ministry of Science and Technology of China, among others. The authors are Xie Jingchun (CUHK), Zhan Yan (CUHK, corresponding author), Gong Shengxia (Shanghai Astronomical Observatory, Chinese Academy of Sciences), Huang Chengli (Shanghai Astronomical Observatory; School of Astronomy and Space Science, University of Chinese Academy of Sciences) and Zhang Jian (NWU-HKU Joint Centre of Earth and Planetary Sciences, The University of Hong Kong).
Mercury in enhanced colour, built from NASA MESSENGER images. The colours are not what your eye would see – they are boosted to bring out differences in the rocks at the surface. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
A cliff called Carnegie Rupes, almost 2 km tall, slices through a crater 105 km wide. Cliffs like this form when a planet’s surface is squeezed. Colours show height (red = high, blue = low). (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
How the plains changed. (a) The surface stretches and lava erupts as hot mantle rises. (b) As the rising rock fades, the surface is squeezed instead. (Credit: Xie et al., Nature Communications, 2026)
Dr Xie Jingchun (left) and Professor Zhan Yan discuss their Mercury research.
