The northern smooth plains were first mapped in detail by NASA’s MESSENGER spacecraft, which orbited Mercury between 2011 and 2015. The plains are among the youngest large-scale geological units on the planet, with crater-counting ages suggesting emplacement roughly 3.7 to 3.9 billion years ago, near the tail end of the period of intense bombardment that sculpted the early solar system. Their smooth appearance in image data is deceptive. Close inspection of the terrain reveals a dense population of tectonic structures—wrinkle ridges, graben, and lobate scarps—that record multiple, superposed episodes of deformation. On the Moon, comparable mare basalt provinces are far less tectonically active; their deformation is dominated by simple contraction from cooling and global shrinkage. Mercury’s northern plains, by contrast, tell a much more complicated story.

The team behind the new study, led by Jianghui Xie with co-authors including Yan Zhan and Shun Dai’s collaborator Gong, approached the problem by combining geologic mapping of the plains’ deformation patterns with numerical models of Mercury’s thermochemical evolution. Their central hypothesis is that a mantle upwelling—a broad, buoyant plume of hot silicate material rising through Mercury’s convecting mantle—developed beneath the northern hemisphere early in the planet’s history. Such an upwelling would have done two things simultaneously. First, it would have driven partial melting of the mantle, generating the enormous volumes of basaltic melt that erupted to form the plains in the first place. Second, it would have dynamically supported topography and imparted extensional stresses on the overlying lithosphere, stretching the crust and allowing the plains’ distinctive patterns of graben and normal faults to form.

The critical insight of the new work is what happened afterward. Because Mercury is a small planet—only about 4,880 kilometers across—it has a comparatively small volume relative to its surface area, meaning it sheds heat efficiently. Interior models indicate that Mercury’s mantle cooled rapidly during the first billion or two years of solar system history, and its convective vigor declined dramatically. The upwelling that once fed the northern plains was therefore not a permanent feature but a transient one. As the planet’s interior cooled, the upwelling waned: it weakened, spread laterally, and eventually lost its capacity to dynamically support the crust above it. The consequence was a reversal of the stress field at the surface. Where extension had once stretched the crust, now gravitational loading of the thick volcanic plains and the withdrawal of dynamic support subjected it to compression.

That stress reversal is the signature written into the plains themselves. The researchers’ analysis shows that deformation structures in the northern smooth plains record both early extensional features—graben and troughs that opened as the crust was pulled apart atop the rising plume—and later compressional features, including wrinkle ridges and thrust-faulted scarps that formed as the crust was squeezed. The magnitude of the later compression is striking: shortening strains inferred from the ridged terrain substantially exceed what global contraction alone could deliver. Mercury’s interior has cooled and contracted since the plains formed, producing the planet’s famous network of lobate scarps, but the local deformation in the northern plains is too intense and too spatially concentrated to be explained by global shrinkage alone. A waning upwelling, the authors conclude, provides the missing piece.

The numerical modeling underpinning the study solves the coupled equations of mantle convection with temperature- and pressure-dependent viscosity, tracking how Mercury’s mantle evolves as radiogenic heat production declines and the planet loses its primordial heat. The models demonstrate that a hemispheric-scale upwelling is a natural outcome of Mercury’s early mantle dynamics, particularly given the planet’s unusually iron-poor bulk composition and its thin silicate shell over a large iron core, which together shape the convection pattern. As the models run forward in time, the upwelling systematically weakens; dynamic topography subsides; and the stress state at the base of the volcanic pile flips from dominantly extensional to dominantly compressional. The predicted deformation history matches the observed superposition relationships in the plains, where extensional structures are cut or buried by younger compressional ones.

This work has implications well beyond Mercury. The northern smooth plains are one of the best-preserved examples in the solar system of a large flood-basalt province on a terrestrial planet, comparable in some respects to Earth’s Deccan or Siberian traps, though far older and better exposed. On Earth, plate tectonics continuously overprints and destroys the record of mantle plume activity; on the Moon, basaltic plains formed in a context where mantle convection had already largely ceased. Mercury sits in between: a one-plate planet with vigorous-enough early convection to generate plume-driven volcanism, but with a rapid enough cooling history to preserve the full arc of a plume’s life cycle—from uplift and eruption through subsidence and compression—in a single geologic archive.

The findings also speak to a broader question in planetary science: how do interior dynamics of small planets manifest at the surface? Mercury has proven to be anything but the dead, inert world once imagined. MESSENGER revealed pyroclastic deposits suggesting volatile-rich explosive volcanism, hollows formed by volatile loss from the surface, and a magnetic field generated in a partially molten outer core. The new study adds another dimension, showing that deep mantle circulation directly sculpted the planet’s largest volcanic province, and that the decline of that circulation is recorded as clearly as the circulation itself. Mercury’s crust, in effect, is a seismogram of its own dying mantle plume.

There are also consequences for interpreting upcoming data. ESA and JAXA’s BepiColombo mission, currently en route to Mercury with arrival planned for 2026, will carry instruments capable of measuring the planet’s gravity field, topography, and composition at higher resolution than MESSENGER. A waned upwelling should leave detectable fingerprints in all three: residual mass anomalies in the mantle, subtle long-wavelength topographic relief across the northern hemisphere, and compositional heterogeneity inherited from the plume-fed volcanism. The new modeling provides a concrete set of predictions that BepiColombo’s measurements can test, potentially allowing scientists to constrain Mercury’s present-day mantle viscosity and thermal state directly from surface observations.

For the general reader, the study offers a vivid reminder that planetary surfaces are not frozen snapshots but records of deep, slow-motion processes. The ridges and troughs crisscrossing Mercury’s northern plains formed over hundreds of millions of years, as a column of hot rock rose, fueled cataclysmic eruptions, and then faded as a small planet bled its heat into space. What remains is a landscape compressed between two eras—stretched by a plume that no longer exists, and squeezed by a planet that is still shrinking. Deciphering that record required the combined power of high-resolution spacecraft imagery, precise topographic measurements, and state-of-the-art geodynamic simulation, and it demonstrates how much of a planet’s history can be recovered from its deformed crust alone.

As Mercury continues to lose its primordial heat, its lobate scarps are still growing, and its plains are still shortening by infinitesimal amounts each year. The new research shows that the magnitude and pattern of that deformation cannot be understood as a simple consequence of cooling alone; it is the compound product of global contraction superimposed on the collapse of dynamic support from a waning mantle upwelling. In reconstructing that sequence, the authors have transformed the northern smooth plains from a puzzling anomaly into one of the most informative natural laboratories for studying the coupling between mantle convection and surface tectonics on any one-plate world—and they have set the stage for the next generation of exploration at the solar system’s innermost planet.

Rift valleys are key tectonic markers. On Earth, they accompany plate boundary stretching and can evolve into systems such as the African Rift Valley. On Venus, comparable rift structures can stretch for thousands of kilometers, reaching up to about 10,000 km, implying the planet has experienced large-scale crustal deformation.

A major uncertainty has been timing: geoscientists have often treated many rift-related features as ancient remnants. The new study suggests a different possibility for at least some regions, where deformation may still be ongoing or have only recently slowed. This would align the surface record more closely with an active mantle.

The research team, led at ETH Zurich by Professor Taras Gerya, used a newly developed high-resolution, three-dimensional computer model to simulate rifting. Unlike earlier approaches that relied on simplified assumptions and mostly two-dimensional setups, the new framework reproduces rift geometry in greater physical detail.

In the simulations, “rift flanks”—the raised areas flanking rift valleys—form particularly when the rift system is young and either actively extending or has only just stopped. The model also indicates that rifts can widen faster than earlier estimates, at roughly 3 to 10 centimeters per year.

After movement ceases, the flanks rapidly flatten through crustal relaxation rather than the erosion-driven smoothing familiar on Earth. This helps explain how Venus can preserve steep, high-relief tectonic topography without the long-term weathering that dominates terrestrial landscapes.

The researchers further note that the simulated flank morphology matches observations from radar imaging of Venus’s surface collected by NASA’s Magellan mission in the 1990s. Such consistency strengthens the argument that Venus’s rifting is not merely ancient history.

Overall, the study concludes that Venus remains geologically active and that its interior is more dynamic than previously believed. The results can help prioritize targets for future exploration aimed at mapping where tectonics may still be reshaping the surface.

With NASA and ESA planning new Venus missions, these insights arrive at a crucial moment. Understanding active rifting will also inform broader questions about how rocky planets evolve—information relevant even to the search for rocky exoplanets.

Subject of Research: Venus tectonics; recent active rifting and rift flank formation
Article Title: Recent active rifting on Venus revealed by wide rift flank uplifts
News Publication Date: 2026
Web References: http://dx.doi.org/10.1038/s41561-026-02044-8
References: Nature Geoscience
Image Credits: NASA/JPL/USGS

Keywords

Venus, rift valleys, tectonic activity, 3D geodynamic modeling, rift flanks, crustal relaxation, Magellan radar, planetary geology, Nature Geoscience, EnVision

At the heart of the PROTEUS framework lies a seamless coupling between SPIDER, a sophisticated model of planetary interior evolution, and AGNI, a cutting-edge atmosphere model grounded in radiative–convective equilibrium physics. The synthesis of these models permits a fully self-consistent portrayal of how mantle dynamics, phase transitions, and volatile partitioning interact with atmospheric composition and escape mechanisms across geologic timescales. Crucially, the approach incorporates state-of-the-art thermochemical equilibrium calculations accounting for volatile solubility in magma oceans, which dominate the interiors of molten super-Earths like L 98-59 d.

The research team assumes that the primordial protoplanetary nebula has already dissipated, focusing instead on the secondary atmosphere’s evolution driven by outgassing, volatile partitioning, and ongoing atmospheric escape. The volatile budget, including elements essential for habitability such as carbon, hydrogen, nitrogen, and sulfur (CHNS), is initialized based on plausible planetary parameters consistent with observational constraints. By simulating these complex interactions, the study circumvents the need to model volcanic outgassing from fully solidified mantles, a process orders of magnitude less efficient than degassing from magma oceans, which remain prevalent in the scenarios examined.

SPIDER is tasked with tracking the planet’s molten mantle, composed primarily of MgSiO3 melt, along an initial adiabatic temperature profile before evolving it in response to various heating mechanisms. These include radiogenic decay, core cooling, and particularly tidal heating, which they model with the Maxwell viscoelastic rheology using LOVEPY software. This rheological treatment accounts for mantle viscosity variations dependent on melt fraction and temperature, yielding realistic heating profiles that can maintain large-scale mantle melt fractions over billions of years. Interestingly, the mantle is considered chemically inert in the current simulations, thus simplifying the thermodynamic calculations while focusing on physical processes.

The core-mantle structure draws analogies with Earth but incorporates adjustments for exoplanet-specific conditions such as mantle pressure and potential incorporation of lighter elements into the core, which modulate core density relative to pure iron. The researchers highlight that, for L 98-59 d, the core mass is approximately 0.66 Earth masses, with the mantle mass closer to 1.48 Earth masses. By holding the planetary interior radius constant over time, they effectively disentangle changes in mantle phase from radius evolution, streamlining the model without sacrificing realism in capturing thermal evolution dynamics.

Atmosphere modeling is managed by AGNI which simulates radiative and convective heat transport through a thick, outgassed atmosphere. The team deploys SOCRATES, a state-of-the-art correlated-k radiative transfer code with 48 spectral bands and angle-dependent treatment, to accurately calculate the net atmospheric energy flux even under dense, volatile-rich atmospheric conditions. Rayleigh scattering and basaltic surface emissivity are integrated, adding correction factors that realistically simulate planetary albedo and infrared emission. The code employs mixing-length theory for convective transport, ensuring that atmospheric heat fluxes balance with the mantle’s thermal output, closing the energy budget at each time step.

Stellar evolution is intimately tied to planetary atmospheric dynamics, and the researchers accordingly incorporate L 98-59’s properties through the MORS stellar evolution model. MORS realistically tracks the star’s luminosity, radius, and extreme ultraviolet (XUV) flux evolution, critical parameters influencing atmospheric escape and surface temperature. With a stellar mass of 0.273 solar masses and a rotation period of approximately 81 days, L 98-59 evolves in a way that gradually reduces its high-energy emissions. This temporal modulation directly affects the rate of hydrodynamic escape from the planet’s atmosphere, providing a dynamic context for volatile retention or loss over billions of years.

The simulations commence at an assumed planetary age of 50 million years, a juncture where the initial rapid atmospheric boil-off has subsided and volatile inventories stabilize. This choice reflects current understanding that early escape processes strongly deplete primordial hydrogen envelopes, after which secondary atmospheres evolve via outgassing and escape. The simulations continue until either mantle solidification occurs or the system reaches the present estimated age of about 4.94 billion years. This timescale ensures that the model encompasses the crucial phases during which volatile partitioning and escape shape the planet’s final atmospheric composition and bulk density.

A pivotal component of the volatile evolution modeled involves atmospheric escape driven by stellar XUV flux. Employing the classic energy-limited photoevaporation formula, the framework calculates the mass-loss rate based on the planet’s gravitational potential and the effective radius at which XUV photons are absorbed. The escape efficiency is fixed near 10%, consistent with high-fidelity hydrodynamic simulations that account for cooling effects in the upper atmosphere. Notably, the atmospheric composition is assumed to escape en masse without fractionation under intense stellar irradiation, reflecting rapid hydrodynamic flow regimes anticipated for planets receiving high XUV fluxes.

Importantly, although the escape process here is non-fractionating, the elemental composition of the escaping gas reflects that of the atmosphere rather than the mantle or core. This distinction leads to ongoing volatile fractionation within the planet over time, as partitioning between interior and atmosphere varies by element. Such a framework naturally captures how high-molecular-weight elements like sulfur and nitrogen may become enriched or depleted relative to hydrogen, informing interpretations of observational data on atmospheric compositions derived from transit and spectroscopic measurements.

The model’s fidelity extends to accurately estimating the observable planetary radius, often measured near the 20 mbar pressure level, which is where transit measurements effectively probe the atmosphere. By coupling radiative-convective atmospheric profiles with hydrodynamic escape simulations, the approach aligns theoretical predictions closely with observable parameters. The planetary bulk density, an essential metric for assessing volatile content and internal structure, is computed using precise mass-radius relationships driven by the model outputs, enabling direct comparisons with measured densities from transit timing variations and radial velocity data.

One of the most compelling aspects of the study is the comparative analysis between the simulated data and recently revised bulk density estimates of L 98-59 d. Earlier estimates placed the density near 3.45 g/cm³, while newer analyses suggest even lower values around 2.2 g/cm³. The authors caution that their volatile inventory estimates are conservative under the older density assumption, and that the lower density findings only reinforce the conclusion that L 98-59 d harbors a substantial volatile component. This finding challenges traditional models of rocky super-Earths as dry, refractory bodies, instead painting a picture of planets that retain deep magma oceans enriched with volatiles over geological timescales.

Hearteningly, the sensitivity analyses embedded within the study confirm robustness against variations in core size assumptions, escape efficiency, and stellar irradiation conditions. This rigorous testing ensures that the volatile-rich evolutionary pathway is not an artifact of narrow parameter choices but rather a natural outcome given plausible physical inputs. The results broadly support emerging paradigms wherein small, close-in exoplanets sustain magma oceans and thick atmospheres, shaped by their complex interplay with host star environments.

The implications of these findings for exoplanet habitability and characterization are profound. Volatile retention, particularly of water and carbon-bearing species, directly impacts surface conditions and the potential for life-supporting environments. By illustrating how intense early irradiation does not inevitably strip volatile reservoirs completely, the study opens new avenues for probing whether super-Earths orbiting M-dwarf stars could host detectable atmospheres amenable to biosignature searches with forthcoming telescopes.

By meticulously combining interior thermodynamics, atmospheric physics, and stellar evolution into a unified model, this research sets a new benchmark for interrogating the histories of terrestrial exoplanets. It showcases how interdisciplinary approaches, grounded in planetary science and astrophysics, can decrypt the subtle processes shaping alien worlds light-years away. As exoplanet discovery marches forward, tools like PROTEUS and AGNI promise to guide interpretations of ever more detailed observational data, ushering in an era of nuanced understanding of planetary architecture and habitability in the cosmos.

The study’s integration of high-fidelity physical modeling with observational constraints marks a decisive advance in exoplanet science—a realm where bold theories and detailed data increasingly intersect. By demonstrating that L 98-59 d, a world initially thought potentially barren, likely evolved with a thick, volatile-rich atmosphere sustained by a persistent magma ocean, it compels reconsideration of how common such evolutionary trajectories may be throughout the galaxy. This insight challenges prevailing assumptions and invites further exploration into the diversity of rocky exoplanet pathways.

Ultimately, this work exemplifies how modern planetary science deploys computational innovation to unravel the inner lives of distant worlds. With telescopes poised to examine exoplanet atmospheres in exquisite detail, understanding the coupled evolution of interiors and atmospheres will prove indispensable. The volatile-rich evolution scenario posited here therefore not only reshapes our knowledge of a single super-Earth but also propels the broader quest to comprehend planetary habitability, informing strategies to identify promising targets for future observational campaigns.

Subject of Research: Evolution and volatile retention of molten super-Earth exoplanet L 98-59 d through coupled interior-atmosphere modeling.

Article Title: Volatile-rich evolution of molten super-Earth L 98-59 d.

Article References:
Nicholls, H., Lichtenberg, T., Chatterjee, R.D. et al. Volatile-rich evolution of molten super-Earth L 98-59 d. Nat Astron (2026). https://doi.org/10.1038/s41550-026-02815-8

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41550-026-02815-8