Apparently, it’s possible for planets to shrink, and it’s happening within our very own solar system. Mercury, already the smallest planet, is contracting, causing what appears to be shrinkage. According to research from NASA’s MESSENGER spacecraft, the planet closest to the sun has lost about four miles of elevation in some areas.
Scientists have known that Mercury was shrinking since the 1970s when they first saw the planet’s giant cliffs. According to planetary scientist William McKinnon of Washington University in Saint Louis, this shrinking behavior is consistent with the type of planet Mercury is, a huge, iron planet with a thin, outer shell made up of rock.
With a single layer of solid plates on the surface and a molten iron core, the geology of the small planet adds credence to the shrinking theory. Mercury’s surface acts a lot like the skin of an apple; as it dries out, it shrinks. As the core cooled over millions and billions of years, the surface contracted causing the outer crust to fracture and move about to fit the core.
Paul Byrne, a researcher at the Carnegie Institution of Washington and the Lunar and Planetary Institute, states that it’s difficult to know when the shrinkage occurred. It could have started more than 3.8 billion years ago when astronomers believe massive asteroids pelted many of the planets in our solar system, although there are signs that the shrinkage happened after the asteroid collisions. What we do know is that the shrinkage has been happening for a long, long while.
Bryne is the lead author of a paper discussing these results in the March 16 issue of Nature Geoscience.