Mercury, the smallest planet in our Solar System, has been contracting for billions of years. As its interior cools and therefore slowly contracts, its surface deforms, giving rise to landforms known as lobate scarps. These are the surface expression of major faults along which contraction has taken place; they extend for hundreds of kilometres and can reach heights of 2,000 metres.
A new study entitled Graphite lubricates Mercury’s global contraction, published in Nature Communications, shows that this deformation was facilitated by a lubricant hidden within Mercury’s crust: graphite, the same material used in pencil leads. The research was carried out by a team of researchers from the University of Padua, the Italian National Institute for Astrophysics (INAF-OAPD) and the University of Milano-Bicocca.
The work combined analysis of the planet’s surface topography with laboratory friction experiments on rocks similar to those found in Mercury’s crust, carried out at the University of Padua.
The results revealed that graphite-rich layers, inherited from the earliest stages of Mercury’s history, have continued to shape the planet’s tectonics silently up to the present day, and that Mercury may have contracted far more than previously estimated.
«The results suggest that, without graphite, some of the major fault systems observed on Mercury today could not exist in the form in which we see them. More generally, they show how the earliest stages of a planet’s formation can determine the shape of its surface billions of years later,» explains first author Natalia A. Vergara Sassarini, who was affiliated with the University of Padua when the research began and is now at the Italian National Institute for Astrophysics (INAF-OAPD), in research coordinated by Professor Matteo Massironi of the University of Padua.
«We have demonstrated that large fault systems can be controlled by thin films of graphite capable of influencing deformation throughout the planet’s crust, making Mercury a unique world in the Solar System,» adds Telemaco Tesei of the Department of Geosciences at the University of Padua, who was responsible for the mechanical experiments conducted as part of the study.
«Faults on Earth are often “lubricated” by the presence of fluids that facilitate their movement,» observes Andrea Bistacchi of the Department of Earth and Environmental Sciences at the University of Milano-Bicocca, co-author of the study, whose research has also focused on weak faults on Earth, «but fluids such as those found on Earth are not available on Mercury because of its extreme proximity to the Sun and its low gravity. It was therefore necessary to identify an alternative mechanism to explain the weakness of Mercury’s faults.»
«Just a few months before the ESA/JAXA BepiColombo spacecraft is due to enter orbit around Mercury next November, this discovery lays the groundwork for targeted research aimed at examining the geometry of these enormous faults in detail and verifying the presence of graphite in their vicinity. These are precisely the kinds of observations that the SIMBIO-SYS instrument will be able to carry out, making it possible to reconstruct these landforms in three dimensions, observe the surface in extremely fine detail and, at the same time, determine its mineralogical composition,» concludes Matteo Massironi of the Department of Geosciences at the University of Padua, co-author of the paper and Project Scientist for this instrument, which was designed to map and analyse Mercury’s geology, surface and composition.
Link to the research:
https://www.nature.com/articles/s41467-026-75459-x
Title: Graphite lubricates Mercury’s global contraction – Nature Communications – 2026
Authors: Natalia A. Vergara Sassarini, Matteo Massironi, Telemaco Tesei and Andrea Bistacchi