Mercury shrunk by more than 7 kilometers in radius over past 4 billion years

Researchers have claimed that Mercury may have contracted up to 7 kilometers in radius over the past 4 billion years, much more than previous estimates suggested.

Paul K. Byrne and Christian Klimczak at the Carnegie Institution of Washington led a team that used MESSENGER's detailed images and topographic data to build a comprehensive map of tectonic features, which suggested Mercury shrunk substantially as it cooled, as rock and metal that comprise its interior are expected to.

Steven A. Hauck, II, a professor of planetary sciences at Case Western Reserve University and the paper's co-author, said that with MESSENGER, we have now obtained images of the entire planet at high resolution and, crucially, at different angles to the sun that show features Mariner 10 could not in the 1970s.

To help gauge how the planet may have shrunk, the researchers looked at tectonic features, called lobate scarps and wrinkle ridges, which result from interior cooling and surface compression. The features resemble long ribbons from above, ranging from 5 to more than 550 miles long.

Lobate scarps are cliffs caused by thrust faults that have broken the surface and reach up to nearly 2 miles high. Wrinkle ridges are caused by faults that don't extend as deep and tend to have lower relief. Surface materials from one side of the fault ramp up and fold over, forming a ridge. The scientists mapped a total of 5,934 of the tectonic features.

The scarps and ridges have much the same effect as a tailor making a series of tucks to take in the waist of a pair of pants.

With the new data, the researchers were able to see a greater number of these faults and estimate the shortening across broad sections of the surface and thus estimate the decrease in the planet's radius.

The new finding has been published in the journal Nature Geoscience.