Mercury Shrinks More Than Previously Estimated
New research suggests the planet has contracted by over 14 miles as its core cools over 4.5 billion years.
Updated on Oct. 15, 2026 in Geology
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A new study published in Geophysical Research Letters indicates that Mercury has shrunk significantly more than scientists previously thought. Researchers now estimate the planet's diameter has contracted by more than 14 miles.
Why it matters
Understanding the scale of Mercury's contraction provides critical insights into the cooling process of its metallic interior. This revision helps geologists better map the tectonic history of the 4.5-billion-year-old planet.
The new study suggests Mercury may have shrunk 10 to 30 percent more than previous estimates indicated. Researchers utilized a surface roughness map to account for geologic disruptions and asteroid impacts that obscured tectonic structures.
The players
Paul Byrne
He is a planetary scientist who conducted a 2014 study estimating the contraction of Mercury.
BepiColombo
It is an international space mission currently gathering data to clarify the interior structure of Mercury.
The details
Researchers developed a map of Mercury's surface roughness to identify tectonic wrinkles that were previously obscured by debris from asteroid impacts and resurfacing events. As the planet loses thermal energy over billions of years, its interior atoms draw closer together, causing the planet to contract.
Timeline
2014: Paul Byrne published a study estimating 9 miles of contraction.
October 2018: The BepiColombo mission launched.
October 15, 2026: The research findings were published.
The Big Picture
This finding updates the baseline data for the BepiColombo Laser Altimeter mission, which is designed to measure surface topography more precisely. This research challenges existing models of planetary cooling for rocky planets within the Milky Way.
Future observations from the BepiColombo mission will refine our understanding of how rocky planets evolve and lose thermal energy over time. These findings help scientists build more accurate models for the structural history of planetary bodies.
The takeaway
The study demonstrates how surface debris from asteroid impacts can hide evidence of large-scale geologic shifts. By re-evaluating these obscured regions, scientists can more accurately reconstruct the history of planetary contraction.
Further reading
Learn more about the latest developments in Geology.
Source note: This article includes information reported by Discover Magazine.
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