Mercury is shrinking faster than previously estimated
Analysis of surface 'wrinkles' suggests the planet's diameter has decreased by up to 14.5 miles as its interior cools.
Mercury is contracting at a rate 10% to 30% faster than scientists previously believed. New research indicates that the planet's diameter has decreased by up to 14.5 miles (23 kilometers) since its formation, a significant increase over previous estimates of 2.5 to 10 miles.
The findings center on the planet's surface "wrinkles," known as lobate scarps and ridges. These geological features serve as the primary evidence of planetary shrinkage. According to the research, asteroid bombardment over billions of years created debris and craters that obscured these scarps, particularly in the roughest regions of the surface. This masking effect led researchers to underestimate the total amount of contraction occurring on the planet.
The cooling process
Mercury formed approximately 4.5 billion years ago. As the planet's interior cools over eons, the material contracts, creating thrust faults that manifest as the ridges and scarps seen on the surface. While earlier estimates were based on data from NASA's MESSENGER probe, a new analysis of surface roughness reveals that many of these critical indicators were hidden by impact debris, leading to the revised, higher contraction figures.
Implications for planetary composition
Determining the precise extent of Mercury's shrinkage is critical for scientists attempting to model the planet's internal structure. The degree of contraction provides a direct window into what lies beneath the crust. Gaku Nishiyama of the German Aerospace Center (DLR) Institute of Space Research noted that more shrinking suggests Mercury could have a larger metal core, a higher starting temperature, or fewer light elements, such as silicon, mixed into that metal core.
Future outlook
These revised figures challenge existing models of how the smallest planet in the solar system evolved. By refining the contraction rate, researchers can better determine the ratio of metal to rock in Mercury's interior. Future observations will likely focus on identifying more of these hidden scarps to further calibrate the planet's cooling history and internal composition.