Mercury Shrinkage Update
New data reveals Mercury shrank up to twenty-three kilometers as its interior cooled.
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Key Points
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Some of Mercury’s contraction scarps are enormous: they can rise up to 1 mile (1.6 kilometers) high and extend for hundreds of miles.
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BepiColombo consists of linked European and Japanese spacecraft that will separate after entering Mercury orbit for a more comprehensive survey; its laser instrument is expected to help verify the planet’s contraction.
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Before BepiColombo, only two spacecraft had visited Mercury: NASA’s MESSENGER in the 2010s and Mariner 10 in the 1970s.
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Hannes Bernhardt of the University of Maryland, who was not involved in the study, said Mercury offers lessons about the formation and evolution of large rocky bodies such as Earth that may be learned there better than anywhere else in the solar system.
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Lead author Gaku Nishiyama said the contraction estimate is a key observable for testing models of Mercury’s evolution because the planet’s development has been driven by cooling; he added that the interior may preserve clues about the formation of the innermost solar system.
Mercury, the solar system's smallest planet, has shrunk far more than scientists previously thought. New research shows the planet lost 12 to 14 miles (19 to 23 kilometers) in diameter over the past 4.5 billion years—roughly 10% to 30% more than earlier estimates NBC News. The dramatic contraction happened as Mercury's hot interior cooled down, but impact craters buried much of the evidence.
Researchers compared geological contraction features with surface-roughness maps from NASA's MESSENGER mission. They discovered that debris from billions of impacts roughened and hid scarps and ridges formed by the planet's global shrinkage Time. The revised findings could reshape our understanding of Mercury's internal makeup and whether it has a larger metal core or started hotter than previously thought.
Why Mercury Shrank So Much More Than Expected
Mercury's contraction scarps are massive—some tower up to 1 mile high and stretch for hundreds of miles across the surface NBC News. As the planet cooled from its formation, it contracted and created wrinkles and ridges. But heavy bombardment from space rocks filled craters with loose debris that buried and obscured these contraction features.
Lead researcher Gaku Nishiyama explained that contraction is the key measurement for testing models of Mercury's evolution Qazinform. The planet's entire history is driven by cooling. Hidden contraction features mean earlier surveys missed roughly 10% to 30% of the planet's actual shrinkage.
What Greater Shrinkage Reveals About Mercury's Core
The larger-than-expected contraction suggests three possibilities about Mercury's interior Time. First, the planet may have a proportionally larger metal core than scientists thought. Second, the core may contain fewer light elements like silicon. Third, Mercury's initial temperature when it formed may have been hotter than models predicted.
Because cooling and contraction are directly linked, this measurement helps scientists distinguish between competing theories of Mercury's formation NBC News. Understanding the planet's interior composition also reveals clues about how the entire inner solar system formed billions of years ago.
BepiColombo Mission Will Verify the New Estimate
Only two spacecraft have visited Mercury before: NASA's MESSENGER in the 2010s and Mariner 10 in the 1970s NBC News. The European-Japanese BepiColombo mission is set to begin orbiting Mercury in November with far more advanced instruments. It consists of linked European and Japanese spacecraft that will separate after entering orbit for comprehensive mapping.
BepiColombo carries a laser instrument that will measure Mercury's topography with unprecedented detail Time. It will pinpoint contraction scarps and ridges hidden or distorted by impact debris. These precise measurements will test the new shrinkage estimates and refine models of Mercury's thermal history and internal structure.
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