Masked tectonic structures suggest Mercury contracted 40% more than its visible scars alone indicate
The surface of Mercury is filled with craters, ridges and steep cliffs. Over billions of years, as the planet's interior cooled, the planet also shrank. Just as the skin of a drying fruit wrinkles when what is inside it shrinks, Mercury's rocky surface crumpled into ridges and cliffs as its interior cooled and the planet contracted. Mercury has quite literally grown smaller with age.
New research indicates that Mercury has contracted by about 40% more than previously estimated based on visible tectonic features alone. Scientists from Hokkaido University, the German Aerospace Center, and The University of Tokyo have found that Mercury's rocky surface, which crumpled as the planet cooled and shrank over billions of years, may have obscured some of the tectonic structures used to calculate its shrinkage.
By mapping shortening structures, such as ridges and scarps, and comparing them with maps of surface roughness, researchers discovered that these tectonic features are more commonly identified in smoother terrain than in rougher regions. This suggests that the planet's contraction record might be incomplete due to the obscuring effect of rough terrain.
When accounting for the influence of surface roughness, Mercury's estimated radial contraction increases from 8.3 kilometers to 11.6 kilometers, a 40% higher projection than based on visible structures alone. The true contraction value could be even larger. These findings provide new insights into Mercury's geological evolution and highlight the importance of correcting for surface roughness when studying planetary contraction. Future observations from the BepiColombo mission may further refine the picture.
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