NASA scientists just found more proof the Mercury has been shrinking.

Using stereo images from NASA's MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft to create a high-resolution topo map, the scientists were able to identify the so called "Great Valley."

"Unlike Earth's Great Rift Valley, Mercury's great valley is not caused by the pulling apart of lithospheric plates due to plate tectonics; it is the result of the global contraction of a shrinking one-plate planet," said Tom Watters, senior scientist at the Smithsonian National Air and Space Museum, in a press release. Watters is also the lead author of the study published in Geophysical Research Letters.

According to the paper describing their findings, the 400-kilometer-wide valley which extends into the Rembrandt basin, one of the largest and youngest impact basins on the planet, was formed as the Mercury cooled and bulged.

Explaining how this is possible, Cosmos Magazine said that unlike Earth's lithosphere which can shift around and pulled apart, Mercury's does not. Instead, the latter's lithosphere is considered a "one giant plate that encapsulates the entire world." Great Valley was formed as a result of the folding of the planet's outermost shell in response to global contraction or shrinking.

Cooling of Mercury's interior caused two large fault ‘scarps' -- cliff-like land structures that resemble stairs -- to form. The sagging valley floor lowered part of the rim of the Rembrandt basin as well.

"Even though you might expect lithospheric buckling on a one-plate planet that is contracting, it is still a surprise when you find that it's formed a great valley that includes the largest fault scarp and one of the largest impact basins on Mercury," Watters explained.

The study provides the first evidence of buckling of the planet's outer silicate shell in response to this global contraction.

"There are similar examples of this on Earth involving both oceanic and continental plates, but this may be the first evidence of this geological process on Mercury," Watters said.