New findings indicate that Mercury has shrunk by up to seven kilometers in radius over the past four billion years. Previous estimates led researchers to believe it had only shrunk by one or two kilometers.
The qualifier "rapidly" may be a little misleading when dealing with geologic time scales, but the planet closest to the Sun has indeed been shrinking at a rate several times greater than previously believed. Over the past four billion years, Mercury has shrunk by up to seven kilometers in radius, according to new evidence gathered by NASA's MESSENGER spacecraft.
The new finding was published in the journal Nature Geoscience Sunday, March 16 and has actually helped resolve a discrepancy in theory and observation. Previous estimates based on Mariner 10 data suggested that Mercury had only lost one to two kilometers, which didn't match up with models of the planet's formation and aging.
"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," said Steven A. Hauck, II, a professor of planetary sciences at Case Western Reserve University and the paper's co-author.
Paul K. Byrne and Christian Klimczak at the Carnegie Institution of Washington have led a team that used MESSENGER's detailed images and topographic data to build a comprehensive map of tectonic features. Called scarps and ridges, the mapped features are similar to the tucks that a tailor makes to take in the waist of a pair of pants. Based on this new data, the team estimates the planet has contracted between 4.6 and 7 kilometers in radius.