Mercury's buried surface wrinkles suggest the planet shrank 10 to 30 percent more than estimated
A Geophysical Research Letters study says buried wrinkles suggest Mercury may have shrunk 10 to 30 percent more than experts thought. Lead author Gaku Nishiyama says the larger contraction suggests a core that started extremely hot and is mostly metal.
The Scientist · Science desk
Mercury's estimated diameter loss goes up from as much as 9 miles, in Byrne's 2014 paper, to more than 14 miles in the revision by Nishiyama's team.
| Measure | Value | As of | Claim |
|---|---|---|---|
| Byrne: shrank as much as | 9 miles | 2014 | 6 |
| Nishiyama: shrank more than | 14 miles | 7 |
What happened
- Mercury's shrinking comes from interior cooling, and the brittle crust buckles into ridges and scarps that planetary scientists count as shortening structures.
- Nishiyama's team mapped surface roughness and found shortening structures are less common in rough terrain, and the team says resurfacing events such as asteroid impacts obscured many of them.
- The work puts the loss in Mercury's diameter above 14 miles, revising upward an earlier figure of as much as 9 miles.
Why it matters
- What it limits constraint Interior models that use total contraction as a clue to Mercury's makeup and evolution now have a larger number to fit.
- What it sets up precedent Discover says the same hiding effect probably applies to Mars, the moon and exoplanets; the only test it describes is on Mercury.
- Who's exposed exposure Contraction totals built from how common visible wrinkles are, the method used in the past, are exposed to the same undercount wherever craters and debris cover them.
The lead author did not expect the pattern to be so clean. "I was expecting some correlations" between surface roughness and missing wrinkles, said Nishiyama, a planetary scientist at the German Aerospace Center's Institute of Space Research, "but I was not expecting such a very clear correlation." [4][8]
A correlation across a map says that rough ground and missing wrinkles go together. The burial explanation is the team's reading of it, and the intuitive one [5]. Discover's account does not describe how a roughness map becomes a corrected total, so the 10 to 30 percent figure cannot be checked from the article [3].
The article gives the correction in two sizes, and they are not obviously the same comparison. The percentage is set against what experts thought [3]. The mileage is set against a 2014 Nature Geoscience paper by Paul Byrne of Washington University and colleagues, which concluded the diameter had shrunk by as much as 9 miles [6].
The authors consider their number a lower bound [9]. Mercury's tectonic record is sketchy, and Discover reports that the new roughness map likely still fails to capture all the details an accurate measurement needs [10]. In our view the direction of the correction is secure, because structures that are hidden can only add to what the visible ones show. The size is the open part, and it inherits any gaps in the roughness map.
On the interior, Nishiyama was careful. "This is still an ongoing topic," he said, "because disentangling the many parameters of Mercury's interior is not easy." [14]
What to watch
- BELA topography of Mercury, which Nishiyama says will measure the surface more precisely and could test how much the roughness map misses.
- Whether the roughness correction is applied to Mars or the moon, where the same undercount is suspected but untested.
- Whether interior models revise the core's starting temperature and light-element content to fit the larger contraction.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence50
- Adoption
- Insufficient
- Hype gap+15
- Incentives
- Insufficient
- Confidence45
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
As Mercury's interior cools and the planet contracts, its brittle crust buckles into ridges and scarps, the wrinkle-like features called shortening structures.
- [2]
A new study in Geophysical Research Letters finds Mercury's shortening structures are more widespread than previous estimates recognized, but difficult to spot beneath impact craters and debris.
- [3]
The study suggests Mercury may have shrunk 10 to 30 percent more than experts thought.
- [4]
Gaku Nishiyama, lead author of the paper, is a planetary scientist at the German Aerospace Center's Institute of Space Research.
- [5]
Nishiyama's team created a map of Mercury's surface roughness and found shortening structures are less common in rough terrain, indicating many wrinkles have been obscured by resurfacing events such as asteroid impacts.
- [6]
A 2014 Nature Geoscience paper by Paul Byrne of Washington University and colleagues concluded that Mercury's diameter had shrunk by as much as 9 miles.
- [7]
Nishiyama's work revises Byrne's 2014 figure of as much as 9 miles upward, to more than 14 miles.
- [8]
Nishiyama said: "I was expecting some correlations" between surface roughness and missing wrinkles, "but I was not expecting such a very clear correlation."
- [9]
The researchers argue their calculation may still underestimate the effect and consider it a lower bound rather than the final word.
- [10]
Because Mercury's tectonic record is sketchy, it is likely the new map of surface roughness still fails to capture all the details needed for an accurate measurement.
- [11]
Nishiyama noted that the BepiColombo Laser Altimeter (BELA), launched by the European Space Agency in October 2018, is nearing Mercury after eight years and will allow researchers to measure surface topography more precisely.
- [12]
The prevalence of shortening structures has been used to estimate Mercury's contraction in the past.
- [13]
Nishiyama said the team's findings suggest Mercury's core started out extremely hot and is composed predominantly of metal, with fewer light elements like silicon.
- [14]
Nishiyama said: "This is still an ongoing topic," "because disentangling the many parameters of Mercury's interior is not easy."
- [15]
The amount of Mercury's shrinkage is a clue to the makeup and evolution of its interior.
- [16]
Discover says that if surface roughness has skewed previous estimates of Mercury's contraction, the same is probably also true of rocky worlds in general, including Mars, the moon and exoplanets.
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Sources
1 independent publisher whose own reporting we read for this story.
- discovermagazine.comMercury's Hidden Surface Wrinkles Suggest the Planet Shrank More Than Previously Thought
1 article · October 15, 2026
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