A new study challenges the long-standing scientific consensus that Mercury is geologically dead.
For decades, Mercury carried the reputation of being a dead and dry planetwhose geological history ended a long time ago. Its cratered surface, sun-beaten and seemingly frozen in time, seemed to tell a story of ancient violence followed by billions of years of silence. This story just got considerably more interesting.
A team led by Dr. Valentin Bickel from the University of Bern discovered about 400 bright lines that run along the slopes of Mercury’s surface. These “lines” are not just interesting geological curiosities, but potentially active formations, driven by volatile materials escaping from beneath the planet’s crust. The was published in Communications Earth & Environment.
The discovery emerged from an ambitious project that analyzed approximately 100,000 high-resolution images captured by NASA’s Messenger probe, which orbited Mercury between 2011 and 2015. Using machine learning to systematically map these features for the first time, researchers found clear patterns in where and how the lines appear.
The lines are concentrated on the sun-facing slopes of relatively young impact craters, specifically those that drilled through the volcanic surface layers until reaching the bedrock potentially rich in volatiles. They often originate from glowing depressions called “cavities”, which are believed to be formed by the release of gases. The correlation with solar heating suggests that solar radiation plays a crucial role in triggering the release of these underground materials.
Researchers propose that volatile substances such as sulfur and other light elements are being expelled from the interior of Mercury through networks of fissures created by meteorite impacts. When solar radiation heats these exposed regions, it drives the volatiles to the surface, where they escape into space, leaving behind the characteristic glowing bands.
This fundamentally changes our understanding of Mercury. Instead of a static world that has exhausted its geological activity eons ago, Mercury appears to be continually lose material from within in a dynamic process that is happening now.
The discovery comes at a good time, as the European Space Agency’s BepiColombo mission is currently on its way to Mercury, carrying instruments designed and built in part at the University of Bern. When it arrives, BepiColombo will photograph the same regions that MESSENGER photographed, allowing researchers to see whether new stretch marks have formed in recent years.
If they have graduated, this will provide direct evidence of ongoing geological activity on Mercury, proving that even small, seemingly dead worlds can harbor secrets about planetary processes that we are only beginning to understand.
As with many aspects of science, a discovery often raises more questions than it answers. How much matter is the planet losing? How long has this process been taking place? And what does this mean for the long-term evolution of rocky planets near their stars? As we find more small, inhospitable worlds orbiting distant suns, Mercury’s ongoing activity may offer clues about processes unfolding across the Galaxy.
