Study: Mercury has shrunk nearly 12 kilometres since its birth

Mercury’s radius has decreased by nearly 12 kilometres since the planet formed about 4.6 billion years ago, as its interior gradually cooled, according to a study by researchers at Hokkaido University.

The findings were published Thursday in the U.S. scientific journal Geophysical Research Letters, according to Japan Times.

Mercury, the smallest planet in the Solar System, currently has a radius of about 2,440 kilometres. Observations by NASA’s MESSENGER spacecraft and other instruments have confirmed the presence of numerous wrinkle ridges across its surface, geological features formed as the planet’s crust contracted.

Previous attempts to estimate Mercury’s shrinkage have relied on the length and other characteristics of these contractional features. However, researchers noted that such estimates may have underestimated the planet’s overall contraction because the features are unevenly distributed across its surface.

To address this issue, Gaku Nishiyama, a postdoctoral researcher at Hokkaido University, developed a new analytical approach based on the possibility that some contractional features have been obscured by craters created by meteorite impacts and by lava eruptions.

The research team measured the degree of surface roughness produced by such geological events and compared the data with the distribution of contractional features.

The analysis showed that contractional features tend to be scarce in areas with highly rugged terrain, including regions around craters.

After accounting for this relationship, the researchers estimated that Mercury’s radius has decreased by nearly 12 kilometres since the planet’s formation.

Further observations could refine that estimate. BepiColombo, a joint Japan-European mission to explore Mercury, is scheduled to arrive at the planet in November. The spacecraft will conduct high-precision observations of Mercury’s terrain.

“We believe that the estimated shrinkage of the radius will increase as the mission provides more detailed observations of the planet’s topography,” Nishiyama said.

By Tamilla Hasanova