Mercury is shrinking 10% to 30% more than previously thought, according to new research published in Geophysical Research Letters. The study, led by Gaku Nishiyama of the German Aerospace Center (DLR) Institute of Space Research, attributes the increased contraction to debris from asteroid impacts obscuring surface wrinkles, which reveal the planet’s cooling and contraction over 4.5 billion years.
The findings, based on data from NASA’s MESSENGER mission, suggest Mercury’s diameter has decreased by up to 14.5 miles (23 kilometers) since its formation, far exceeding earlier estimates of 2.5 to 10 miles (4 to 16 kilometers). This shrinkage could indicate a larger metallic core, fewer light elements like silicon, or a hotter initial temperature, according to Nishiyama.
How Impacts Mask Mercury’s Shrinkage
Mercury’s surface is pockmarked by billions of years of asteroid impacts, creating craters and debris that obscure the geological wrinkles—known as shortening structures—that signal contraction. Researchers combined MESSENGER data with digital models of Mercury’s terrain, discovering that rougher areas had fewer visible wrinkles. It made us think that there’s a process obscuring shortening structures,
Nishiyama said, citing impact debris as the likely culprit.
Mercury is shrinking faster than we thought. What's going
By accounting for these obstructions, the team recalculated Mercury’s contraction, estimating an additional 10% to 30% shrinkage. 30% is a little bit surprising, but the corrected amount of contraction actually makes sense to me,
Nishiyama added. The revised figures align more closely with physics-based predictions about planetary cooling, offering new insights into Mercury’s internal structure.
Implications for Planetary Science
Mercury’s shrinkage could mirror processes on other celestial bodies. If their results hold, then we’ll have taken a step further in investigating planets we can’t yet visit in person, said Paul Byrne, a planetary scientist at Washington University in St. Louis, who was not involved in the study. The findings also raise questions about Mercury’s core, which makes up a large portion of its radius, and how its cooling affects surface features like the Caloris Planitia, a 1,550-km-wide impact basin.
Mercury Has Wrinkles That Show It's Shrinking. Now, Scientists
BepiColombo’s Role in Unraveling Mercury’s Secrets
Future data from the BepiColombo mission, a joint effort by the European Space Agency and Japan Aerospace Exploration Agency, could refine these estimates.
What Remains Uncertain
The planet Mercury is shrinking far faster than we
While the study provides a clearer picture of Mercury’s contraction, uncertainties persist.
As BepiColombo’s data accumulates, scientists hope to answer these mysteries, shedding light on Mercury’s evolution and its place in the solar system’s history.
The study, published in Geophysical Research Letters on September 10, builds on data from NASA’s MESSENGER spacecraft, which orbited Mercury from 2011 to 2015. Mercury, which formed around 4.5 billion years ago, is the smallest planet in the solar system, with a diameter of approximately 3,032 miles. Its surface is covered in craters and ridges, which scientists use to study its geological history.
Mercury’s extreme proximity to the Sun and its high surface temperatures—reaching up to 800°F (430°C) during the day—make it challenging to study.
The research underscores the importance of planetary science in understanding the processes that shape rocky worlds. By studying Mercury’s contraction, scientists gain insights into the planet’s core composition and the broader dynamics of planetary evolution. As new data emerges from BepiColombo, the scientific community anticipates further breakthroughs in unraveling Mercury’s mysteries.