Surface release of radiatively active particles, with high infrared- (IR-)to-visible extinction ratios, has been proposed as a method of warming Mars. However, to warm Mars using aerosols, particles released locally must disperse globally. Here we provide an initial reference study in a plume tracking, dry Martian atmospheric model to address this question. The winds that transport aerosols respond to the aerosol's IR forcing, implying strong radiative-dynamical feedbacks (RDF). We investigate RDF from surface release of two particle compositions: carbon (graphene) and metal (Al). Self-lofting helps particles rise and spread locally and regionally, and the Hadley cell strengthens under warming, aiding latitudinal mixing. Within our model, Mars RDF enable engineered-aerosol warming. Warming is slightly greater for three-dimensional vs. 1D-models and also depends on spectral resolution of radiative transfer. We assess implications for Mars warming. Many open atmospheric science questions remain, including the role of agglomeration, dry-deposition rate uncertainty, and modeling water cycle feedbacks.

Recent papers by Ansari et al. (2024, Science Advances 10, eadn4650) and Richardson et al. (2025, arXiv eprint 2504.01455) have suggested that global warming of the Martian surface ('terraforming') by 35 K to sustain local habitats above the melting point of water could be achieved through the injection of engineered aerosols into the Martian atmosphere. Using the MarsWRF 3D Global Climate Model, we investigate how artificial warming of Mars through engineered aerosol release would affect the planetary water cycle and the distribution of the major surface ice reservoirs. Within our model framework, every 20 K of global warming induces a tenfold increase in atmospheric water vapour content due to sublimation of H2O ice from the North Polar Cap. This increases the potency of cloud radiative feedbacks which induces nighttime warming ( 5-10 K) at low latitudes, but daytime cooling (up to 40 K) in the winter midlatitudes. Water is transferred from the edge of the North Polar Cap to the South Polar Cap and there is minor destabilisation of shallow northern midlatitude subsurface ice. As a result, seasonal sublimation of H2O ice from the South Pole has an increased impact on the global water cycle. These changes persist on Mars at least decades after loading of the atmosphere with engineered aerosols ceases. Our model is limited by the gaps in our knowledge of present-day Martian weather and climate, and of the microphysics and radiative properties of candidate warming agents. Much more data is therefore needed before warming Mars could become feasible.

The James Webb Space Telescope (JWST) has opened a new era in the study of rocky exoplanets, enabling direct characterization of their surfaces with mid-infrared spectroscopy. Different types of rock have distinct spectral features that are diagnostic of the chemical composition and other physical properties like surface texture. Measurements of these features can provide valuable clues about a planet's geologic history and interior processes. Here we report a JWST 5-12-mu m thermal emission spectrum for the rocky exoplanet LHS 3844 b. It is best matched by a dark, low-silica surface, such as basalt or other olivine-rich materials. The spectrum rules out surfaces covered by fresh, small-sized grains (powders); however, space weathering can darken the powders and make them more consistent with the data. The data also disfavour trace concentrations of CO2 or SO2 gas (with 5 sigma and 3 sigma upper limits of 100 mbar and 10 mu bar, respectively). Taken together, these results are well fit by an old, space-weathered surface with no evidence of accumulated volcanic gases.

Martian rocks are known to contain sulfur-bearing species, including sulfates and sulfides. These compounds record a sulfur cycle that operated over the geological evolution of Mars. We used the Curiosity rover to investigate a deposit of light-toned stones in Gediz Vallis within Gale crater on Mars and found that the stones are composed of native sulfur. The sulfur deposit appears to have formed in place, within a sinuous entrenched canyon cut into the floor of Gediz Vallis. The presence of native sulfur implies that a sulfur enrichment pathway involving buoyant subsurface fluids operated on ancient Mars. We propose that the primary source of this sulfur was magmatic vapor, which cooled in the near subsurface cryosphere and was released by decompression during the erosion of Gediz Vallis.

“Lava worlds”, Earth-sized planets hot enough ( T _eq ≳ 1100 K) to melt their dayside silicate surfaces, have emerged as promising candidates for atmospheric detection and characterization. Thermal emission observations show an apparent dichotomy: The hottest lava worlds have colder daysides than the temperature of a maximally emitting bare rock, indicating the likely presence of thick and/or reflective atmospheres, while the coldest ones do not. However, where in instellation flux this potential bifurcation occurs is uncertain. We present a JWST/MIRI Low Resolution Spectrometer eclipse of the ultra-short-period (USP) lava world HD 3167 b ( T _eq = 1786 K, R = 1.6 R _⊕ , P = 0.96 day) that helps bridge this gap. We measure the white-light eclipse depth to be 38 ± 11 ppm, more than 5 σ lower than the expected eclipse depth of a dark, maximally hot bare rock. We use this to derive a dayside brightness temperature that is best explained by the presence of an atmosphere that cools the dayside by reflecting incoming starlight and/or efficiently redistributing heat to the planet’s nightside. An atmosphere is further compatible with the planet’s slight underdensity compared to an Earth-like composition. The corresponding dayside emission spectrum is not precise enough to constrain atmospheric composition, motivating follow-up spectroscopic observations with JWST/NIRSpec. Lastly, we use our observation and existing data to refine key planetary parameters of the HD 3167 system. HD 3167 b is currently the least irradiated USP super-Earth with evidence for an atmosphere.

How the ancient climate of Mars transitioned to its current cold, hyperarid state is recorded by the sedimentary rocks preserved on its surface. Gale crater, the Curiosity rover landing site, is one such location, where the central mountain, Aeolis Mons, preserves an extensive sedimentary record. Curiosity has demonstrated that the Aeolis Mons succession comprises older, fluvio-lacustrine facies overlain by younger, aeolian facies, inferred to reflect a broad aridification trend. From orbit, multiple canyons and sediment fans are observed originating from Gale's crater rim and Aeolis Mons itself, suggesting regional, intermittent returns to wet conditions, late in the crater's history. Curiosity recently investigated Gediz Vallis, a canyon incised into Aeolis Mons, which contains a central ridge hypothesized to be a degraded alluvial fan. We use Curiosity's remote sensing suite to test this orbital hypothesis, by investigating the characterizing these canyon-filling, sedimentary deposits in an upslope region of Gediz Vallis, Arc Pass. Here, the rover conducted an extensive campaign and was able to resolve fine-scale sedimentary facies and textures. We find these deposits consist of transported breccias and conglomerates, and record multiple sediment transport processes, including debris flows and landslides, separated by episodes of aeolian erosion and in-situ alteration. The debris flow deposits, preserved as levees and channels, require the continued, but likely intermittent, surface water availability, during the exhumation phase of Aeolis Mons, late in the history of both Gale crater and Mars. The processes recorded here are likely to be representative of regional, paleoclimatic conditions across Gale crater.

The cause of Mars’s loss of surface habitability is unclear, with isotopic data suggesting a ‘missing sink’ of carbonate 1 . Past climates with surface and shallow-subsurface liquid water are recorded by Mars’s sedimentary rocks, including strata in the approximately 4-km-thick record at Gale Crater 2 . Those waters were intermittent, spatially patchy and discontinuous, and continued remarkably late in Mars’s history 3 —attributes that can be understood if, as on Earth, sedimentary-rock formation sequestered carbon dioxide as abundant carbonate (recently confirmed in situ at Gale 4 ). Here we show that a negative feedback among solar luminosity, liquid water and carbonate formation can explain the existence of intermittent Martian oases. In our model, increasing solar luminosity promoted the stability of liquid water, which in turn formed carbonate, reduced the partial pressure of atmospheric carbon dioxide and limited liquid water 5 . Chaotic orbital forcing modulated wet–dry cycles. The negative feedback restricted liquid water to oases and Mars self-regulated as a desert planet. We model snowmelt as the water source, but the feedback can also work with groundwater as the water source. Model output suggests that Gale faithfully records the expected primary episodes of liquid water stability in the surface and near-surface environment. Eventually, atmospheric thickness approaches water’s triple point, curtailing the sustained stability of liquid water and thus habitability in the surface environment. We assume that the carbonate content found at Gale is representative, and as a result we present a testable idea rather than definitive evidence.

Observations of the hot rocky exoplanet 55 Cancri e report significant but unexplained variability in brightness across visible and infrared bands, e.g., on subweekly timescales, its mid-infrared brightness temperature fluctuates by approximately 1,400 K (with hundreds of Kelvin uncertainty). We propose a magma temperature-cloud feedback as a potential explanation that relies on the planet's atmosphere and surface. In this feedback, under cloud-free conditions, stellar radiation heats surface magma, releasing silicate vapor that condenses into clouds. Once formed, these clouds attenuate stellar insolation, thereby cooling the surface, reducing vapor supply, and decreasing cloudiness. A time lag between surface temperature increase and cloud formation, likely due to lagged atmospheric transport of cloud-forming vapor, enables self-sustained oscillations in surface temperature and cloudiness. These oscillations manifest as variations in both the planet's thermal emission and reflected starlight, causing variability in secondary eclipse depths across wavelengths without significantly affecting the transit depth. Using a simple model, we find that diverse planetary parameters can reproduce the observed infrared brightness variability. We also demonstrate that brightness at different wavelengths can oscillate out of phase, consistent with recent observations by the James Webb Space Telescope. Additionally, we propose that time-varying and spatially nonuniform cloud cover can result in changing amplitude and phase offset of the planet's phase curve, potentially explaining observations. Finally, we discuss observational strategies to test this proposed mechanism on 55 Cancri e. If confirmed, these observable ocean-atmosphere dynamics on exoplanets would provide valuable insights into the composition, evolution, and long-term fate of rocky planet volatiles.

Mars' sedimentary rocks record Gyrs of environmental change. New data enable the first global analysis of paleo-environment relevant physical properties of these rocks, including layer thickness and accumulation rate. We find that layer thicknesses of post-3.5 Ga sedimentary rocks across the Martian surface show coherent variations at 1000 km-scale that are inconsistent with simple volcanic and climatic hypotheses for formation, which are consistent with global compositional homogeneity at orbital scales. These data, in combination with new analyses of outcrop age and total rock volume demonstrate a global decrease in layer thickness that predates the eventual drop off in preserved sedimentary rock volume per Myr. The new constraints confirm a diachronous transition in Mars' global sedimentary rock record while also highlighting a regional dichotomy in young sedimentary rock deposits that has not been quantified before.

The Amapari Marker Band (AMB) is a layer within the Mount Sharp stratigraphy that has been mapped around the Gale crater in orbital images and was recently investigated up close by the Curiosity rover. Symmetric wave ripple marks within the AMB indicate a lacustrine depositional environment in the area investigated along the Curiosity traverse. The wavelength and morphology of the ripples constrain the water depth to a few meters or less. The lateral continuity of the ripple unit defines a minimum extent of the lake during ripple formation. The stratigraphy of the AMB is consistent with an environment of increasing water depth during sedimentation and the lateral correlation of the AMB stratigraphy suggests a transgressive depositional system building upon an eroded surface. The location of the AMB within the surrounding aeolian stratigraphy, coupled with the progression of depositional environments through the Mirador formation, records a pattern of a rising water table relative to sedimentation rates. The potential regional extent of the lacustrine environment, based on orbital mapping of the AMB's variable elevation, spans at minimum 2.0 km of the lateral AMB deposit in the area around Marker Band Valley and may have extended up to 14 km to the west across the northern Gale crater.

Wind abrasion is the dominant erosive process inferred from observations by Curiosity during its traverse in Gale crater, but how and how fast wind scours Mount Sharp is unclear. Here, we infer formative wind direction from ventifacts (wind-eroded rock fragments) measured from Curiosity's recent traverse. We compare these measurements to previous ones and to wind model predictions, and attempt to estimate the current rate of wind erosion near Curiosity's location on Mount Sharp. Ventifacts in this study indicate winds blowing south-southeast, agreeing with previous studies on the floor of Gale crater, but differing from studies at the base of the mountain slope. Upslope abrasive wind flows predominate, consistent with idealized models. At some sites, ventifacts are oriented both upslope and downslope on Mount Sharp, suggesting bimodal wind direction at the mountain, agreeing with circulation models that predict diurnal reversals. Using crater-retention age statistics at one site, we estimate a - 3.5 +/- 0.8 mu m/Earth year (yr) upslope horizontal erosion rate at Mount Sharp. We suggest the observed ventifacts formed when Mars' obliquity and climate regime were similar to those in the present day.

Previous investigations along Curiosity's traverse in Gale crater have explored the relationship between orbital and in situ observations. This work aims to better understand the geologic environment of units only observable from orbit and compare them to the properties of units examined by Curiosity. Here, we map an erosion-resistant dark-toned mantling unit that overlies the modern topography of Aeolis Mons (informally known as Mt. Sharp) and compare this unit to two other previously mapped dark-toned resistant units, the marker band and the mound skirting unit (MSU), that have been inferred to represent different geologic environments (lacustrine and aeolian, respectively). Visible to short wave infrared spectra from the Compact Reconnaissance Imaging Spectrometer for Mars and visual images from the High Resolution Imaging Science Experiment and Context Cameras aboard the Mars Reconnaissance Orbiter are used for this comparison. Spectral data suggest a mafic composition with minor alteration, although the composition varies more with location around Mt. Sharp rather than between units. Morphologically, the mantling unit has strong similarities to the marker band based on their consistent low-albedo, erosion-resistance, and smooth appearance, contrasting with the highly variable surface texture of the MSU. We hypothesize that all three units had a similar sediment source but experienced aqueous alteration at different times: early ubiquitous cementation in a surface aqueous environment in the mantling unit and marker band versus patchy late diagenesis in the MSU. If true, these results suggest that water activity continued within the Gale crater long after the erosion of Mt. Sharp.

Observations of the ultra-short period rocky exoplanet 55 Cancri e (55 Cnc e) indicate that the planet's dayside infrared radiation fluctuates by a factor of at least six on sub-weekly timescales, for unknown reasons. We propose a feedback mechanism where increased reflective clouds cool surface magma, subsequently reducing cloud formation, which may offer a potential explanation for these phenomena. In this mechanism, under less cloudy conditions, stellar radiation heats the surface magma, causing it to release more silicate vapor, which then condenses to form reflective clouds. Once formed, these clouds reduce stellar insolation at the surface, leading to surface cooling, which in turn reduces vapor supply, decreasing cloudiness. A time lag between the temperature increase of surface magma and the subsequent increase in cloudiness (likely due to lagged atmospheric transport of cloud-forming vapor) enables self-sustained oscillations in surface temperature and cloud reflectivity. These oscillations manifest as variations in both the emitted thermal radiation and the reflected stellar radiation, causing variability in secondary eclipse depths across different wavelengths without significantly affecting the transit depth. Using a simple model, we find that diverse planetary parameters can reproduce the observations. Additionally, we demonstrate that secondary eclipse depths at different wavelengths can oscillate out of phase, consistent with recent observations by the James Webb Space Telescope. Finally, we discuss observational strategies to test this proposed mechanism on 55 Cancri e. If confirmed, observable ocean-atmosphere dynamics on exoplanets would open a new window into the composition, evolution, and fate of rocky planet volatiles.

TOI-561 is a galactic thick-disk star hosting an ultra-short-period (0.45-day-orbit) planet with a radius of 1.37 R ⊕, making it one of the most metal-poor ([Fe/H] = −0.41) and oldest (≈10 Gyr) sites where an Earth-sized planet has been found. We present new simultaneous radial velocity (RV) measurements from Gemini-N/MAROON-X and Keck/HIRES, which we combined with literature RVs to derive a mass of M b = 2.24 ± 0.20 M ⊕. We also used two new sectors of TESS photometry to improve the radius determination, finding R b = 1.37 ± 0.04 R ⊕ and confirming that TOI-561 b is one of the lowest-density super-Earths measured to date (ρ b = 4.8 ± 0.5 g cm−3). This density is consistent with an iron-poor rocky composition reflective of the host star’s iron and rock-building element abundances; however, it is also consistent with a low-density planet with a volatile envelope. The equilibrium temperature of the planet (∼2300 K) suggests that this envelope would likely be composed of high mean molecular weight species, such as water vapor, carbon dioxide, or silicate vapor, and is likely not primordial. We also demonstrate that the composition determination is sensitive to the choice of stellar parameters and that further measurements are needed to determine whether TOI-561 b is a bare rocky planet, a rocky planet with an optically thin atmosphere, or a rare example of a nonprimordial envelope on a planet with a radius smaller than 1.5 R ⊕.

The presence of perennially wet surface environments on early Mars is well documented1,2, but little is known about short-term episodicity in the early hydroclimate3. Post-depositional processes driven by such short-term fluctuations may produce distinct structures, yet these are rarely preserved in the sedimentary record4. Incomplete geological constraints have led global models of the early Mars water cycle and climate to produce diverging results5,6. Here we report observations by the Curiosity rover at Gale Crater indicating that high-frequency wet-dry cycling occurred in early Martian surface environments. We observe exhumed centimetric polygonal ridges with sulfate enrichments, joined at Y-junctions, that record cracks formed in fresh mud owing to repeated wet-dry cycles of regular intensity. Instead of sporadic hydrological activity induced by impacts or volcanoes5, our findings point to a sustained, cyclic, possibly seasonal, climate on early Mars. Furthermore, as wet-dry cycling can promote prebiotic polymerization7,8, the Gale evaporitic basin may have been particularly conducive to these processes. The observed polygonal patterns are physically and temporally associated with the transition from smectite clays to sulfate-bearing strata, a globally distributed mineral transition1. This indicates that the Noachian-Hesperian transition (3.8-3.6 billion years ago) may have sustained an Earth-like climate regime and surface environments favourable to prebiotic evolution.

The climate of a planet can be strongly affected by its eccentricity due to variations in the stellar flux. There are two limits for the dependence of the inner habitable zone boundary (IHZ) on eccentricity: (1) the mean stellar flux approximation (S-IHZ proportional to root 1 -e(2)), in which the temperature is approximately constant throughout the orbit, and (2) the maximum stellar flux approximation (S-IHZ proportional to (1 - e)(2)), in which the temperature adjusts instantaneously to the stellar flux. Which limit is appropriate is determined by the dimensionless parameter Pi = C/BP, where C is the heat capacity of the planet, P is the orbital period, and B = partial derivative Omega/partial derivative T-s, where Omega is the outgoing long-wave radiation and T-s is the surface temperature. We use the Buckingham Pi theorem to derive an analytical function for the IHZ in terms of eccentricity and Pi. We then build a time-dependent energy balance model to resolve the surface temperature evolution and constrain our analytical result. We find that Pi must be greater than about similar to 1 for the mean stellar flux approximation to be nearly exact and less than about similar to 0.01 for the maximum stellar flux approximation to be nearly exact. In addition to assuming a constant heat capacity, we also consider the effective heat capacity including latent heat (evaporation and precipitation). We find that for planets with an Earthlike ocean, the IHZ should follow the mean stellar flux limit for all eccentricities. This work will aid in the prioritization of potentially habitable exoplanets with nonzero eccentricity for follow-up characterization.