Smithsonian Magazine · People & society

Mercury's Shrinkage May Be Greater Than Previously Estimated

Scientists analyzing data from NASA's MESSENGER mission suggest Mercury, the smallest planet and closest to the sun, has shrunk significantly more than previously thought due to its cooling over billions of years.

New research indicates Mercury's width may have decreased by 10 to 30 percent, a loss of up to 14.5 miles, which is considerably more than earlier estimates of 2.5 to 10 miles. This revised figure could offer new insights into the planet's interior and evolution, potentially shedding light on other rocky celestial bodies.

Mercury is challenging to study due to its proximity to the sun, which complicates spacecraft trajectories and limits close-up observation. The MESSENGER mission, orbiting from 2011 to 2015, provided the primary data for this research.

The study combined MESSENGER data with a digital terrain model. Researchers found that rougher surface areas showed fewer wrinkles, suggesting that debris from impacts might be obscuring the signs of contraction.

By accounting for these obstructed areas, the team calculated the new shrinkage estimate. This updated figure aligns better with physics-based predictions of Mercury's cooling and contraction.

The revised contraction amount suggests Mercury might have a larger metallic core with fewer light elements or a higher initial temperature than previously believed. Further data from the upcoming BepiColombo mission is expected to provide more clarity.

Understanding Mercury's shrinkage is key to deciphering its geological history, cooling rate, initial size, and composition. This knowledge can contribute to a broader understanding of planetary formation and evolution.

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