FAST READ
- A 2026 study suggests Mercury's diameter may have contracted by as much as 23 km as its interior cooled over geological time.
- The estimate is about 30% larger than earlier shrinkage assessments based mainly on mapped contractional landforms.
- ESA-JAXA's BepiColombo mission is expected to enter Mercury orbit in November 2026 and can test the revised estimate with improved topographic observations.
WHY IN NEWS
- The study uses surface roughness and contractional fault evidence to argue that some shrinkage landforms may have been hidden by later impacts and debris.
- It provides a useful case study in planetary thermal evolution and the way new missions can revise models built from older spacecraft data.
TOP DATA & FACTS
- Mercury's current diameter is about 4,880 km.
- The planet is roughly 4.5 billion years old.
- The new study estimates as much as 23 km of diameter contraction.
- That estimate is about 30% greater than earlier assessments.
- The reported 23 km contraction is approximately 14 miles.
- Mercury is the smallest planet in the Solar System.
- Mercury is the innermost planet, orbiting closest to the Sun.
- Its metallic core is unusually large relative to the planet's radius.
- Cooling of the core, mantle and crust produces global contraction.
- Mariner 10 made 3 Mercury flybys in 1974-75.
- NASA's MESSENGER entered Mercury orbit in 2011.
- MESSENGER ended its mission in 2015.
- Only 2 spacecraft missions had visited Mercury before BepiColombo: Mariner 10 and MESSENGER.
- BepiColombo is a joint ESA-JAXA mission.
- BepiColombo is expected to enter Mercury orbit in November 2026.
PRELIMS
- Mercury is the smallest and innermost planet.
- Planetary contraction can create thrust faults and lobate scarps.
- Cooling causes materials to contract; it does not imply Mercury is losing 23 km of radius each year.
- MESSENGER was a NASA mission.
- BepiColombo is jointly led by ESA and JAXA.
- Planetary fault mapping can be combined with topography and surface-roughness analysis to infer tectonic history.
QUICK REVISION
- Revised maximum contraction: about 23 km in diameter.
- Estimate: roughly 30% above earlier values.
- Mercury diameter: about 4,880 km.