Mercury has shrunk in radius by more than 10 km since its birth, analyzed by Hokkaido University team

Using a new analytical method, a research team at Hokkaido University has discovered that since Mercury was born about 4.6 billion years ago, its radius has shrunk by more than 10 kilometers as its interior cools. The paper was published on the 10th in the American scientific journal Geophysical Research Letters.

The current radius of Mercury is approximately 2,440 km. Observations by the US spacecraft MESSENGER and others have revealed that there are many wrinkle-like topography on the earth's surface caused by shrinkage.

Until now, attempts have been made to estimate the shrinkage rate based on factors such as the length of these terrains, but due to the uneven distribution, there was a possibility that they were underestimated.

Manabu Nishiyama, a doctoral researcher at Hokkaido University, focused on the possibility that after the wrinkles were formed, they were covered up by craters created by meteorite impacts or lava eruptions. The degree of unevenness (roughness) on Mercury's surface caused by meteorite impacts was quantified and compared with the distribution of contracted topography.

As a result, it was found that areas with high roughness, such as near craters, tend to have less contracted topography. Taking this into consideration, it was found that the radius had shrunk by nearly 12 kilometers.