Context
A new study published in Geophysical Research Letters estimates that Mercury may have contracted 10–30% more than previously thought, losing up to 23 km of its diameter since its formation. Impact debris may have hidden some surface evidence of this contraction.
Explanation
- Mercury is the smallest and innermost planet of the Solar System and has an unusually large iron-rich core.
- Since its formation about 4.5 billion years ago, its interior has gradually cooled and contracted, causing the mantle and crust to contract too.
- The rigid crust responds by buckling and faulting, producing characteristic lobate scarps, thrust faults and wrinkle ridges.
- Earlier estimates suggested a 4–16 km decrease in diameter; accounting for contraction features hidden beneath impact debris raises the possible loss to 23 km.
- NASA’s Mariner 10 first visited Mercury, while MESSENGER became the first spacecraft to orbit it.
- BepiColombo, a joint ESA–JAXA mission, will use higher-resolution observations to study Mercury’s surface, interior, magnetic field and contraction history.
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