Mercury has traditionally been considered a completely geologically “dead” planet. Its surface looks dry, heavily cratered, and almost unchanged for billions of years. However, a new study calls this view into question. Scientists have found evidence that the planet is still losing volatile substances and may still retain some internal activity. The research was published in the journal Nature Communications Earth and Environment.

Systematic Analysis of “Slope Streaks”

The study was led by Dr. Valentin Bickel from the Center for Space and Habitability at the University of Bern, together with colleagues from the Astronomical Observatory of Padua. For the first time, they carried out a complete analysis of so-called slope streaks, which are bright elongated features found on the slopes of craters and elevated regions across Mercury’s surface.

To do this, the team applied machine learning methods to nearly 100,000 high-resolution images taken by NASA’s MESSENGER spacecraft between 2011 and 2015. As a result, they created the first full inventory of these structures, identifying about 400 bright streaks and describing their shapes, sizes, and spatial distribution in detail. Bickel explained that previously slope streaks on Mercury were known only from isolated examples, whereas now a complete picture of their global distribution had been obtained for the first time.

What These Streaks Mean

Most of the streaks are concentrated on sunlit slopes of relatively young impact craters. They are especially often associated with bright depressions known as hollows. According to the authors, these structures form as a result of degassing, meaning the release of volatile substances such as sulfur and other light elements from inside the planet.

Impact craters create fractures through which these substances can rise to the surface. Solar heating intensifies the process, causing evaporation and the formation of bright traces. In this way, Mercury is still continuing to lose volatile materials into space even today. Bickel stated that their results indicate Mercury is still losing volatiles to space, which completely changes the idea of the planet as being entirely geologically dead.

Significance for Understanding the Planet

The loss of volatile substances is directly connected to Mercury’s volatile budget, meaning how much gas and light elements the planet loses over time. This is an important factor in the evolution of terrestrial planets. In addition, degassing may be linked to residual internal activity. Although Mercury cooled long ago, some processes in its crust and mantle may still be ongoing.

These conclusions are expected to be tested and refined using data from the BepiColombo mission, a joint project of ESA and JAXA. The spacecraft is already on its way to Mercury and from 2025 onward will begin transmitting images and spectroscopic data of much higher quality than those obtained by MESSENGER.

In Short

Scientists analyzed nearly 100,000 images from MESSENGER and for the first time created a complete map of slope streaks on Mercury, identifying about 400 bright features on crater slopes. These structures form because volatile substances such as sulfur escape from the planet’s interior through fractures created by impacts. The process is still ongoing today, which contradicts the idea of Mercury as a completely dead planet. The discovery changes our understanding of the evolution of the planet closest to the Sun and awaits confirmation from the BepiColombo mission.