Mercury Is Shrinking: Newly Discovered Great Valley Hints It

Planetary scientists have discovered a new large valley on Mercury, the first evidence that may hint the buckling of the planet's outer silicate shell as it contracted.

In a new study, scientists from the Smithsonian Institution and countries such as the United States, Germany and Russia, used a high-resolution topographic map of the planet's southern hemisphere taken by stereo images from NASA's MESSENGER spacecraft.

Is Mercury Shrinking?

Just like a plum where wrinkles form as a result of aging, the planet would form deep valleys, as a result of global contraction. For comparison, the Earth's crust consists of the lithosphere that can shift around because of tectonic plates.

However, Mercury does not have these plates as its lithosphere consists of one giant plate. As a result of the cooling and contraction of the planet's core and interior, the outer capsule crumpled.

No Evidence, Until Now

"There are examples of lithospheric buckling on Earth involving both oceanic and continental plates, but this may be the first evidence of lithospheric buckling on Mercury," said Thomas Watters, lead author of the study, said in a press release by the American Geophysical Union (AGU).

The 400 kilometer-wide valley spreads into the Rembrandt basin, one of the largest and youngest impact basins on Mercury. Rembrandt basin is crosscut by the largest fault scarp on the planet, Enterprise Rupes, and another scarp complex, called Belgica Rupes, that extend to the valley's rim. Such scarps have also been found on the Earth's Moon, indicating that it might be shrinking, too.

"Understanding the mechanical structure of the lithosphere and mantle provides important constraints on buckling and localization instability models that may account for long-wavelength, low-amplitude folding of the lithosphere and the localization of widely spaced thrust faults," the researchers concluded in the study published in the journal Geophysical Research Letters.

The MESSENGER spacecraft launched in August 2003. For 12 years, it observed and snapped photographs of Mercury. However, the spacecraft crashed into Mercury's surface in 2015.