12.09.2026
"It made us think that there's a process obscuring shortening structures."
Wrinkles on the surface of Mercury have revealed that the closest planet to the sun is shrinking faster than scientists thought.
New research suggests that Mercury is shrinking between 10% and 30% faster than had been previously estimated. The team behind this research calculated that the planet has lost nearly 12 miles (19 kilometers) of its total diameter since it formed.
The researchers think that the extremity of this shrinking has gone unnoticed previously because bombardment from space rocks over time has created craters that obscured the evidence of this process.
NASA's Messenger spacecraft spots an apparently fresh crater on Mercury during its early orbits on March 29, 2011. (Image credit: NASA/JHUAPL/CIW)
Scientists say determining the extent of the shrinking of Mercury is key to investigating the composition of the planet's interior.
"More shrinking means Mercury could have a larger metal core, less light elements like silicon mixed into the metal core, or a higher starting temperature," team leader Gaku Nishiyama, of the German Aerospace Center (DLR) Institute of Space Research said in a statement.
Mercury's rocky past
Like all rocky planets in the solar system, Mercury was formed 4.5 billion years ago during a violent and turbulent time in the solar system's history, as rocks and asteroids collided with each other and were bound together.
These impacts generated heat, which Mercury has been losing ever since. As the interior of Mercury cooled, it also shrank. This caused geological wrinkles in the form of scarps and ridges to develop in the rocky outer layers of Mercury.
This cooling should result in Mercury shrinking in a roughly uniform way, and that would make these shortening structures common across the planet. However, asteroid impacts throughout its history have not only created craters that obscure signs of its geological history, but have also spread debris across the surface of Mercury. This makes wrinkles tougher to spot among the accumulation of billions of years' worth of geological features.
The team combined previous maps of Mercury's geology with new observations of the entire planet's surface roughness. They found the roughest terrain of Mercury featured the fewest wrinkles.
"It made us think that there's a process obscuring shortening structures," said Nishiyama, who thinks that impact debris in the roughest regions of Mercury is covering shrinking wrinkles.
The team then used the ridges and scarps in regions less affected by the dispersal of debris to estimate the amount of contraction. This indicated that missing features in rough areas could amount to 10% to 30% extra shrinkage over the 4.5 billion-year lifetime of Mercury. That amounts to a total change in diameter of up to 14.5 miles (23 kilometers) rather than the currently estimated 2.5 to 10 miles (4 to 16 kilometers).
"30% is a little bit surprising, but the corrected amount of contraction actually makes sense to me," Nishiyama said.
There may be more surprises in store. Nishiyama believes that the updated figures could still be an underestimate. This estimate is based on data collected by NASA's MESSENGER probe, which ended in 2015. MESSENGER could only distinguish features larger than around 3 miles (5 kilometers) across.
In November 2026, the BepiColombo mission will start conducting scans of Mercury's surface in much higher resolution than this, and that could reveal even more shrinkage features.
The team's research was published on Thursday (Sept. 10) in the journalGeophysical Research Letters.
Quelle: SC
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Previous studies may have underestimated how much Mercury has contracted as the planet cooled over billions of years because its rough surface hides some of the geological evidence.
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. And, 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.
These geological and topographical features found on the planet’s surface have also preserved a record of how Mercury has evolved. Scientists have long used them to study the planet’s geological history.
New research led by Hokkaido University, in collaboration with the German Aerospace Center (DLR) and The University of Tokyo, suggests that Mercury has contracted by about 10 to 30 percent more than the previous estimates suggested. The team found that the planet’s rough surface may have obscured some of the tectonic structures used by scientists to calculate its shrinkage. The findings were published in Geophysical Research Letters.
Among the geological features found on Mercury are something that scientists call shortening structures, these are the ridges and scarps created when the planet’s crust was squeezed as its interior cooled and contracted.
By mapping these structures, scientists can estimate how much Mercury’s radius has decreased. However, the researchers found that shortening structures are much more commonly identified in smoother terrain than in rougher regions, suggesting that some of the planet’s tectonic record might have been obscured.
“Mercury’s surface preserves a record of how the planet has cooled and contracted, but we found that this record is incomplete,” says Gaku Nishiyama, lead author of the study. “We compared a global map of Mercury’s surface roughness with maps of shortening structures and contraction. Once we account for the effect of rough terrain, Mercury appears to have shrunk considerably more than what the visible tectonic record alone suggested.”
A particularly clear pattern emerged when the researchers looked at relatively young impact craters. When a large impact occurs, surface material can get thrown across the surrounding area, forming rough deposits called ejecta. These deposits can cover older tectonic structures and make them harder to see. Around the Rachmaninoff crater, for example, shortening structures are less common in areas covered by rough ejecta. Some also become less visible closer to the crater, suggesting that they may be partly buried by impact material.
After accounting for the relationship between surface roughness and visible tectonic structures, the estimated radial contraction of Mercury increased from 8.3 kilometers to 11.6 kilometers. The researchers suggest that this figure may still be an underestimate and that the actual contraction could be greater.
The findings provide new insights into Mercury’s geological evolution.
Future observations from BepiColombo, the joint Japan-Europe mission to Mercury, may help refine the picture further. The BepiColombo Laser Altimeter, or BELA, will measure surface roughness at much finer scales and could reveal relationships between much younger geological events and tectonic structures that have so far been difficult to detect completely.
The same effect could also be relevant on other rocky worlds, particularly the Moon, whose surface is even rougher than Mercury’s.
Quelle: Hokkaido University