New Study Reveals How Solar Tidal Forces Shape Mercury's Crust

Mercury, the closest planet to the Sun, continues to intrigue scientists with its unique geological features. Recent research conducted by a team from the University of Bern has unveiled that the Sun's tidal forces significantly influence the planet's crustal deformation. This groundbreaking study, published in the Journal of Geophysical Research: Planets on June 20, 2025, details how Mercury's proximity to the Sun has shaped its surface over billions of years.

Mercury is not only the smallest planet in our solar system but also faces extreme gravitational stresses due to its orbit around the Sun. The research team, led by Liliane Burkhard, a researcher in the Space Research and Planetary Sciences Division at the Institute of Physics at the University of Bern, developed physical models of Mercury to analyze how solar tidal forces contribute to the development of tectonic features.

"These orbital characteristics create tidal stresses that may leave a mark on the planet’s surface," stated Burkhard. The study emphasizes that while thermal contraction has historically been viewed as the primary cause of Mercury's geological features, the newly identified tidal stresses play a crucial role in shaping the planet's surface.

Historically, Mercury has been a subject of fascination due to its rugged, cratered landscape, characterized by towering cliffs and extensive fracture lines. These features have long puzzled scientists, who have primarily attributed them to cooling and contraction processes. However, Burkhard and her colleagues argue that the planet's unique orbital characteristics—with an orbital period of approximately 88 Earth days and an eccentric orbit tilted at about 7 degrees—create variable tidal forces that contribute to its tectonic patterns.

The study utilized models simulating Mercury's geological history over the past four billion years. The findings indicate that the gravitational pull of the Sun induces stress on Mercury's crust, impacting its tectonic features and leading to shifts in the planet's surface. Burkhard noted, "Tidal stresses have been largely overlooked until now, as they were considered too small to play a significant role. Our results show that while the magnitude of these stresses is not sufficient to generate faulting alone, the direction of the tidally induced shear stresses is consistent with the observed orientations of fault-slip patterns on Mercury’s surface."

The implications of this research extend beyond Mercury. Burkhard asserts that understanding how tidal forces affect a planet's geological features can provide insights into planetary evolution across the solar system. "Understanding how a planet like Mercury deforms helps us understand how planetary bodies evolve over billions of years," she explained.

Future missions, such as the BepiColombo mission—launched in October 2018 as a collaboration between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA)—aim to gather more data on Mercury’s surface. This mission will be only the third spacecraft to explore Mercury, a feat complicated by the planet's extreme proximity to the Sun.

As scientists continue to unravel the mysteries of Mercury's geological history, the recent findings highlight the importance of considering a range of factors—beyond thermal processes—that influence planetary surfaces. The evolution of Mercury serves as a vital case study in understanding broader planetary dynamics in our solar system.