Japanese scientists estimate Mercury’s radius has shrunk by nearly 12 km
A team at Hokkaido University in Japan has found that since Mercury formed about 4.6 billion years ago, its radius has decreased by nearly 12 kilometers. The researchers link this to the cooling of the planet’s interior, The Japan Times reports.
A new method of assessment
Mercury’s current radius is about 2,440 kilometers. Observations by the US Messenger probe and other instruments confirmed the presence of numerous wrinkle ridges on the planet’s surface, formed as a result of ground compression.
Previously, the scale of the planet’s contraction was estimated based on the length and other characteristics of these structures. However, because of their uneven distribution, such calculations could underestimate the actual figure.
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The impact of craters and lava
Gaku Nishiyama, a postdoctoral researcher at Hokkaido University, applied a new method focusing on the likelihood that compression structures could have been concealed by craters formed by meteorite impacts and lava eruptions. The team measured the surface roughness created by such processes and compared these data with the distribution of compression features.
The researchers found that there are generally fewer such structures in areas with high terrain roughness, including near craters. Taking this pattern into account, they estimated that Mercury’s radius had contracted by nearly 12 kilometers.
Further observations
The BepiColombo spacecraft of the joint Japanese-European mission is scheduled to arrive at Mercury in November. The mission provides for highly accurate observations of the planet’s terrain, which, according to Nishiyama, could increase the estimate of the contraction of its radius thanks to more detailed topographic data.
