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Mercury shrank 30% more than thought, study finds

By Drooid · Sep 11, 2026, 11:26 PM UTC · How we work

Summary

German Researchers Shrink

German researchers led by Gaku Nishiyama report Mercury has shrunk up to 30% more than previously thought.
They estimate the planet lost up to 14.5 miles (19 km) of diameter since formation.
Combining geological and surface-roughness maps, they infer Mercury’s core may be larger with fewer light elements.
ESA-JAXA BepiColombo, arriving by end of 2026, will collect higher-resolution data to refine shrinkage estimates.

Summary

ESA Commands Separation

ESA’s European Space Operations Centre commanded the Mercury Transfer Module’s pyrotechnic separation on 3 September 2026, confirmed by Doppler at 14:53 BST.
The separation employed springs to push the module away from the spacecraft.
ESA’s Mercury Planetary Orbiter and JAXA’s Mercury Magnetospheric Orbiter remain stacked for November orbital insertion.
The Mercury Planetary Orbiter will power the craft until Mio separates on 9–10 December 2026, the first dual-orbiter Mercury mission.

History

Historical Context

NASA’s Mariner 10 achieved the first three Mercury flybys in 1974, delivering the planet’s first close-up images and confirming a weak magnetic field—a milestone that stood alone for 33 years. Building on that legacy, ESA and JAXA launched the joint BepiColombo mission in 2018; after six flybys (2021-2025) it will enter Mercury orbit in 2026, extending the mapping and magnetic studies begun by Mariner 10.

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German Researchers Shrink

German researchers led by Gaku Nishiyama report Mercury has shrunk up to 30% more than previously thought.
They estimate the planet lost up to 14.5 miles (19 km) of diameter since formation.
Combining geological and surface-roughness maps, they infer Mercury’s core may be larger with fewer light elements.
ESA-JAXA BepiColombo, arriving by end of 2026, will collect higher-resolution data to refine shrinkage estimates.

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