Mercury has long been cast as the solar system’s burnt-out rock, a relic too small and too close to the Sun to hold many surprises. That caricature is now collapsing. New analysis of NASA’s MESSENGER mission data points to a buried layer of diamonds up to about 16 kilometres, or roughly 10 miles, thick beneath the planet’s crust, and to a world that is still slowly contracting instead of lying geologically dead.
Those twin revelations, a glittering interior and a planet that is still shrinking, are not just curiosities. They hint at a deep link between Mercury’s violent birth, its unusual internal structure and the way it continues to evolve today, and they set up the European and Japanese BepiColombo mission as the decisive test of how radical this new picture really is.
From battered rock to “diamond in disguise”
The starting point for the diamond claim is not a single dramatic image but years of painstaking work with MESSENGER’s global maps and compositional data. Scientists using data from NASA’s Messenger spacecraft have argued that Mercury’s surface is rich in carbon, and that under the extreme pressures created when large asteroids slammed into the young planet, that carbon could have been transformed into a thick subsurface layer of diamond. One analysis, shared by Nov scientists working with NASA’s MESSENGER archive, suggests that this buried layer beneath Mercury’s crust could be as much as 16 kilometres thick, a figure that has been echoed in follow up reporting on the planet as a potential “diamond in disguise”.
The logic is straightforward but startling. Mercury’s outer shell appears to have started with abundant graphite, a soft, carbon rich material that would have floated to the top of a global magma ocean. Over time, repeated impacts would have driven that graphite downward and compressed it. Under the right combination of pressure and temperature, graphite converts to diamond, so a deep, laterally extensive layer is plausible if the original carbon inventory was large enough. Researchers who have examined MESSENGER’s geochemical measurements argue that the inferred carbon content is high enough to support a diamond layer that could be as much as 16 kilometres thick, a scenario highlighted in coverage of the planet’s possible diamond layer.
A shrinking world that refuses to die
The diamond story lands at the same time as a second, equally disruptive finding about Mercury’s present day behavior. High resolution images from MESSENGER’s final low altitude orbits revealed swarms of tiny cliff like features, known as small fault scarps, that cut across craters and smooth plains. These structures are orders of magnitude smaller than the giant lobate scarps that first signaled Mercury’s global contraction, and their crisp appearance suggests they formed very recently in geological terms. NASA’s own analysis of these low altitude images concluded that the small scarps are evidence that Mercury is still tectonically active and still shrinking as its interior cools and contracts.
New NASA funded research has gone further, arguing that Mercury is contracting even today, joining Earth as one of the few rocky bodies in the solar system with ongoing tectonic deformation. The work links the distribution of these small scarps to the planet’s global stress field and to quakes that may still be rattling the crust. That picture, which casts Mercury as small, hot and shrinking, has been highlighted in recent discussions of New NASA research, and it undercuts the long standing assumption that Mercury became geologically inert billions of years ago.
Can diamonds help keep a planet active?
Put together, the idea of a thick diamond rich layer and a planet that is still contracting raises a provocative possibility. If Mercury really does hide up to 16 kilometres of diamond beneath its crust, that layer would have very different thermal properties from the silicate rocks above and below it. Diamond is an excellent conductor of heat, but the geometry and grain structure of a buried layer could still act as a kind of thermal choke point, redistributing heat flow in ways that concentrate stress in the overlying crust. In that sense, Mercury’s interior might behave less like a simple cooling ball of rock and more like a layered circuit board, with the diamond horizon helping to route where energy escapes and where faults are most likely to form.
That is still a hypothesis rather than a proven mechanism, and the current data cannot yet resolve the detailed structure of the proposed diamond layer. What the MESSENGER era has shown, however, is that Mercury’s tectonic features are not randomly scattered. The small fault scarps identified in NASA’s analysis of low altitude images cluster in patterns that match models of a planet that is cooling from the inside out, with a large metallic core and a relatively thin outer shell. Those images, captured before the spacecraft impacted Mercury on April 30, 2015, are central to the argument that the planet is still deforming, and they are documented in NASA’s discussion of the small fault scarps that crisscross the surface.
BepiColombo’s X ray test of a glittering hypothesis
The next decisive step will not come from reprocessing old data but from a new spacecraft that is finally nearing its main science phase. BepiColombo, a joint mission of ESA and JAXA, is built around two orbiters: ESA’s Mercury Planetary Orbiter, known as MPO, and JAXA’s Mercury Magnetospheric Orbiter. After a series of flybys, BepiColombo is set to enter orbit around Mercury in 2026, with the MPO carrying a suite of instruments designed to map the planet’s surface composition, topography and gravity field in unprecedented detail. ESA has already highlighted how the mission’s sixth flyby in Jan 2025 refined the trajectory and provided early imaging, with the full science campaign to follow once the spacecraft is in its final orbit, a milestone described in ESA’s overview of BepiColombo.
The real prize for the diamond question lies in BepiColombo’s X ray and gamma ray spectrometers, which will measure the elemental makeup of Mercury’s surface with far greater precision than MESSENGER could achieve. Charly Feldman at the University of Leicester, who worked on one of the MPO instruments, has described the anticipation around finally seeing whether those instruments perform as designed once the spacecraft is in its harsh inner solar system environment. The mission team expects the MPO’s most powerful instruments to start unpicking Mercury’s secrets in 2026, including the distribution of carbon and other key elements that underpin the diamond layer hypothesis, a prospect outlined in coverage of how MPO will probe the planet.
A crowded 2026 and the race to rewrite Mercury’s story
BepiColombo’s arrival will unfold against a busy backdrop for spaceflight in 2026, with multiple agencies, including NASA, fielding high profile missions. Plans for that year include a Falcon 9 flight carrying two CubeSat type space telescopes by NASA, SPARCS and BlackCAT, alongside other payloads, as well as the crewed Artemis II mission that will send astronauts on a lunar flyby for the first time since Apollo. Those milestones, summarized in projections for 2026 in spaceflight, mean Mercury will be competing for attention with a broader push to extend human and robotic reach throughout the inner solar system.
Yet BepiColombo is poised to stand out because it can directly test whether MESSENGER’s inferred diamond layer is real and whether Mercury’s contraction is still ongoing. The mission is set to begin Mercury orbit in 2026, promising unprecedented X ray data on the planet’s surface and near space environment, and mission scientists have framed this as a long anticipated chance to obtain groundbreaking observations of the innermost world. That expectation has been underscored in recent previews of how BepiColombo is Set To Begin 2026 with Promising Unprecedented Ray Data on Mercury’s composition.
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*This article was researched with the help of AI, with human editors creating the final content.
