On the planet closest to the Sun, astronomers have discovered a vast valley. It appears to have appeared as a result of the compression of the active lithosphere of Mercury.
Mercury, the smallest of the planets in the solar system, continues to shrink. Back in the 1970s, it was suggested that it was cooling and contracting, and a few years ago, observations of the MESSENGER probe confirmed this, showing that over a billion years, the diameter of Mercury decreased by about 14 km.
The lithosphere - the crust and upper layers of the planet's mantle - remains active today, although there is only one lithospheric plate on the tiny planet. This leads to interesting implications, as reported by scientists from the Smithsonian Institution's Thomas Watters team in Geophysical Research Letters. As the core of Mercury slowly cools and contracts in the upper layers of the planet, stresses increase, which raise some parts of the surface and lower others. The huge valley that the authors discovered by analyzing the data from the MESSENGER probe was the result of these processes.
A snapshot of the MESSENGER spacecraft and the constructed three-dimensional model of the "Great Valley" of Mercury and the surrounding landscape / © NASA / Johns Hopkins University APL / Carnegie Institution of Washington / DLR / Smithsonian Institution
With a 3-kilometer depth, it reaches 1000x400 km in size and is not only the largest, but also the youngest lowland on Mercury. Its bottom is quite flat, the boundaries are surrounded by rocky ascents. Unlike the Earth's rift valleys, "The Great Valley of Mercury was not formed as a result of the divergence of lithospheric plates due to active tectonics," says Thomas Waters, "it was the result of the global compression of a single plate."