Icarus最新文献

{"title":"Numerical simulation of asteroid geometry variance on airburst threat","authors":"Sean P. Stokes ,&nbsp;Jason M. Pearl ,&nbsp;Veronika A. Korneyeva ,&nbsp;J. Michael Owen ,&nbsp;Cody Raskin ,&nbsp;Arihant Jain ,&nbsp;Javid Bayandor","doi":"10.1016/j.icarus.2025.116819","DOIUrl":"10.1016/j.icarus.2025.116819","url":null,"abstract":"<div><div>For an atmospheric airburst the primary source of concern when assessing uncertainty is the size and velocity. Determining these properties provides the basis for threat assessment, as the total energy of the asteroid may then be estimated, and the threat investigated thoroughly. Even with clarity as to how much energy an asteroid may deposit, a great deal of uncertainty still exists for the actual energy deposition process. One such source of uncertainty is the geometry of the incoming asteroid. The geometry of an asteroid will alter the stress distribution during entry, which adds uncertainty to when fracture will occur. In this study, we use Smoothed Particle Hydrodynamics to model the atmospheric airburst of Tunguska-scale asteroids with varying geometric profiles, including a sphere, ellipsoid, binary and superellipsoid. Each asteroid is modeled as a homogenous structure with strength. We assess uncertainty through a series of planar 2D simulation cases for each geometry, comparing the source of stochasticity across geometries. A single 3D airburst simulation for each geometry is also analyzed. Additionally, the 3D cases are compared to the highly uncertain Tunguska event, predicting variance in burst height across geometries, but all bounded by theoretical burst heights proposed for Tunguska.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"444 ","pages":"Article 116819"},"PeriodicalIF":3.0,"publicationDate":"2025-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145097720","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Convective flow in Ganymede’s subsurface ocean: Implications for the induced magnetic field and topography","authors":"Jakub Kvorka,&nbsp;Ondřej Čadek,&nbsp;Libor Šachl,&nbsp;Jakub Velímský","doi":"10.1016/j.icarus.2025.116807","DOIUrl":"10.1016/j.icarus.2025.116807","url":null,"abstract":"<div><div>Subsurface oceans of icy moons are inaccessible to direct observation and numerical modeling is currently the only way to study the dynamics of these systems. Here, we present the first comprehensive study of Ganymede’s ocean based on the numerical simulations of thermal convection in a rotating spherical shell, and discuss the implications of the flow circulation for Ganymede’s long-wavelength topography and induced magnetic field. In order to determine the structure of the flow in Ganymede’s ocean, we have performed 128 numerical simulations, varying all relevant control parameters (<span><math><mrow><mi>R</mi><mi>a</mi></mrow></math></span>, <span><math><mrow><mi>E</mi><mi>k</mi></mrow></math></span>, <span><math><mrow><mi>P</mi><mi>r</mi></mrow></math></span>) by at least one order of magnitude. Based on this data set, we predict that the ocean circulation is characterized by a retrograde equatorial jet, meridional circulation cells at low latitudes and narrow upwellings and downwellings in the polar regions. The mean speed of the ocean flow ranges from a few cm/s for a thin (<span><math><mrow><mo>&lt;</mo><mspace></mspace><mn>100</mn></mrow></math></span> km) ocean to 0.8<!--> <!-->m/s for a 500<!--> <!-->km thick ocean. The time-averaged heat flux from the ocean varies with the latitude reaching the maximum at the poles and the minimum at mid-latitudes. Assuming that the heat transfer in the ice shell is dominated by conduction, we determine Ganymede’s long-wavelength topography generated by the uneven heat flux from the ocean. We predict that Ganymede’s polar regions are flat or even elevated and the global topographic pattern is dominated by an equatorial depression and elevations at mid-latitudes. Preliminary calculations of the magnetic field, induced by the flow of the salty ocean in the presence of Ganymede’s internal magnetic field, predict sufficiently large amplitudes to allow their detection by the Juice and Europa Clipper spacecrafts. We demonstrate that the pattern of the flow-induced magnetic field strongly depends on the geometry of ocean circulation, suggesting that accurate magnetic measurements can provide constraints on the dynamics of Ganymede’s ocean.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"444 ","pages":"Article 116807"},"PeriodicalIF":3.0,"publicationDate":"2025-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145119707","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New constraint on Europa’s ice shell: Magnetic signature from the ocean","authors":"F. Daniel ,&nbsp;L. Petitdemange ,&nbsp;C. Gissinger","doi":"10.1016/j.icarus.2025.116792","DOIUrl":"10.1016/j.icarus.2025.116792","url":null,"abstract":"<div><div>Jupiter’s icy moons are believed to host subsurface liquid oceans, and among them, Europa stands out as one of the most promising candidates for extraterrestrial life. Yet, the processes driving oceanic flows beneath its ice shell, as well as the factors controlling the thickness of this ice, remain incompletely understood. One especially distinctive feature of Europa is that its salty ocean is electrically conducting and thus influenced by Jupiter’s time-varying magnetic field, which is believed to drive a large-scale zonal flow. Here, we examine how this magnetically-induced jet affects both the heat flux and the dynamics of the convective flow within Europa’s ocean. We first show that the magnetically-driven jet efficiently transports heat in stably stratified regions near the top of the ocean, and may alter the expected convective scaling laws in deeper layers. Second, by analysing the latitudinal distribution of heat flux and relating it to ice-thickness variations, we make predictions that can be compared with current observations. In anticipation of the upcoming JUICE and Europa Clipper missions, we discuss how improved measurement precision could help further constrain the ocean’s properties and refine our model-based forecasts.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"444 ","pages":"Article 116792"},"PeriodicalIF":3.0,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145097719","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"MRO-MCS observed cold spots during the Martian year 34 global dust storm","authors":"Anirban Mandal ,&nbsp;Jagabandhu Panda ,&nbsp;Nirvan Abhilash ,&nbsp;Bijay Kumar Guha ,&nbsp;Varun Sheel","doi":"10.1016/j.icarus.2025.116809","DOIUrl":"10.1016/j.icarus.2025.116809","url":null,"abstract":"<div><div>The weather and climate on Mars depend heavily on the characteristics of dust, CO₂ ice, and water ice. These aerosols, suspended in the Martian atmosphere, play a critical role in determining the thermal equilibrium, wind circulation, momentum, and mass transfer. The ‘cold spots’ are those radiometrically cold areas where the temperature is less than the CO₂ frost point, and they have the maximum probability of CO₂ ice formation. The CO₂ frost point temperature around the northern autumn varies from ∼136–150 K at the surface, while it varies from 140 to 123 K at an altitude range of 5–30 km above the Martian surface. On Mars, global dust storms (GDS) drastically alter the microphysical characteristics of CO₂ ice aerosols, besides their geographical and vertical distributions. With the help of the Mars Climate Sounder (MCS) onboard NASA's Mars Reconnaissance Orbiter (MRO), an attempt is made to investigate the cold spot regions' vertical, temporal, and spatial variability during the Martian Year 34 GDS for the latitude range 60°-90°N. The GDS impacts solar insolation and modifies the circulation pattern, stimulating cold spot formation. Atmospheric cold spots (ACSs) are confined only to the northern polar region, while the surface cold spots (SCSs) are distributed across the planet. However, the majority of the SCSs are identified near the north polar region due to the northern winter. The GDS prevents the formation of ACSs at lower altitudes, prominently near the north pole (∼80°-87°N), while it encourages their formation at lower latitudes (∼65°-80°N) by shading the insolation. While there is no fluctuation in the total number of SCSs in the vicinity of the north pole, the spatial distribution of SCSs does fluctuate. The GDS impedes the formation of SCSs over the entire planet, especially near the south pole and tropical region. Both ACSs and SCSs start to surge in number after weakening of the GDS in latitude ranges 60°-90°N. These findings help advance the knowledge of CO₂ ice formation by offering new insights relating to the thermodynamical characteristics of the Martian climate system and their association with dust storms.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"444 ","pages":"Article 116809"},"PeriodicalIF":3.0,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145048223","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sound velocities of Anorthite at high pressures and temperatures: Implications for estimating porosity in upper lunar crust","authors":"Peng Chen ,&nbsp;Duojun Wang ,&nbsp;Nao Cai ,&nbsp;Rui Zhang ,&nbsp;Junsheng Ma ,&nbsp;Baocun Wang ,&nbsp;Yinan Sun ,&nbsp;Chunyin Zhou ,&nbsp;Ke Yang","doi":"10.1016/j.icarus.2025.116808","DOIUrl":"10.1016/j.icarus.2025.116808","url":null,"abstract":"<div><div>The porosity of the lunar crust serves as the key to deciphering crucial geological processes such as the Moon's impact history, volcanic activity, space weathering, and the formation and evolution of its internal structure. In this study, we conducted ultrasonic interferometry experiments on polycrystalline anorthite samples under high pressures and temperatures (up to 5.7 GPa and 873 K) using synchrotron radiation technology. We obtained the relationships between the compressional wave velocity (<em>V</em>_<em>P</em>) and shear wave velocity (<em>V</em>_<em>S</em>) of anorthite with varying pressure and temperature. The elastic properties of anorthite were fitted as follows: <span><math><msub><mi>K</mi><mrow><mi>S</mi><mn>0</mn></mrow></msub><mo>=</mo><mn>94.71</mn><mfenced><mn>7</mn></mfenced><mspace></mspace><mi>GPa</mi><mo>,</mo><msubsup><mi>K</mi><mi>S</mi><mo>′</mo></msubsup><mo>=</mo><mn>1.60</mn><mfenced><mn>5</mn></mfenced><mo>,</mo><mi>∂</mi><msub><mi>K</mi><mi>S</mi></msub><mo>/</mo><mi>∂</mi><mi>T</mi><mo>=</mo><mo>−</mo><mn>0.004</mn><mfenced><mn>7</mn></mfenced><mspace></mspace><mi>GPa</mi><mo>/</mo><mi>K</mi><mo>,</mo><msub><mi>G</mi><mn>0</mn></msub><mo>=</mo><mn>46.37</mn><mfenced><mn>3</mn></mfenced><mspace></mspace><mi>GPa</mi><mo>,</mo><msup><mi>G</mi><mo>′</mo></msup><mo>=</mo><mn>0.87</mn><mfenced><mn>1</mn></mfenced><mo>,</mo><mi>∂</mi><mi>G</mi><mo>/</mo><mi>∂</mi><mi>T</mi><mo>=</mo><mo>−</mo><mn>0.007</mn><mfenced><mn>1</mn></mfenced><mspace></mspace><mi>GPa</mi><mo>/</mo><mi>K</mi></math></span>. By integrating these results with the lunar velocity model derived from the Apollo missions, we constructed a porosity model for the upper lunar crust, using anorthite as a representative mineral. The results indicate that the thickness of the lunar regolith (weathered surface layer) is approximately 30 km. Within the top 1 km of the lunar surface, porosity ranges from 30 % to 90 %. At the depth of 1–30 km, porosity ranges from 0 % to 50 %. At the depth of 30–50 km, porosity is less than 10 %. This study provides constraints on the porosity of the lunar surface and offers scientific guidance for the safety and design of future lunar exploration missions.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"444 ","pages":"Article 116808"},"PeriodicalIF":3.0,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145048159","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Excess 40Ar in Chang'e-5 lunar soils suggests a possible origin from Earth wind","authors":"Li Zhao ,&nbsp;Liwu Li ,&nbsp;Chunhui Cao ,&nbsp;Qingyan Tang ,&nbsp;Xianbin Wang","doi":"10.1016/j.icarus.2025.116803","DOIUrl":"10.1016/j.icarus.2025.116803","url":null,"abstract":"<div><div>The abundance of ⁴⁰Ar in lunar soils is significantly higher than the expected values from solar wind implantation and ⁴⁰K decay, a phenomenon known as ⁴⁰Ar excess. Traditionally, this excess is attributed to ⁴⁰Ar generated by the decay of ⁴⁰K within the Moon. This radiogenic ⁴⁰Ar degasses to the lunar surface, where it is ionized by solar radiation and subsequently captured by lunar soils. However, stepwise heating (200 °C–1300 °C) and degassing analyses of noble gas isotopes in Chang'e-5 lunar soils samples reveal the presence of two types of ⁴⁰Ar: one unrelated to ³⁶Ar, likely originating from in situ ⁴⁰K decay in the soils, and another correlated with ³⁶Ar, which may primarily derive from Earth wind. Earth wind, an ion flux formed by the escape of Earth's atmosphere, is thought to be injected onto the lunar surface under the regulation of Earth's magnetosphere. The study proposes that the excess ⁴⁰Ar in lunar soils may primarily stem from the continuous escape of Earth's atmosphere and be injected onto the lunar surface through both the inner and outer regions of Earth's magnetosphere, offering a new perspective for understanding volatile exchange between the Earth-Moon system.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"444 ","pages":"Article 116803"},"PeriodicalIF":3.0,"publicationDate":"2025-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145048226","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Regolith without age? High-resolution regolith depth measurements across lunar maria","authors":"Elizabeth F.M. Atang","doi":"10.1016/j.icarus.2025.116790","DOIUrl":"10.1016/j.icarus.2025.116790","url":null,"abstract":"<div><div>In this work, we test the established hypothesis that lunar regolith depth increases with time because the surface is continually exposed to meteorite bombardment. If this hypothesis is correct, younger surfaces should have thinner regolith than older surfaces. Because many of the regolith depth studies in the literature are for surfaces older than 3 Gy, in this paper, we study Mare regions with a wide range of ages between 1.33 Gy and 3.88 Gy. To measure regolith depths, we used the small crater morphology method based on the work by Oberbeck &amp; Quaide. We found median regolith depths between 1.6 m to 4.0 m across our study sites. Importantly, we did not find any correlation between the thickness of the regolith and the age of the surface within the Mare units we studied. We conclude by discussing whether this result represents a true lack of correlation, which would imply an incomplete understanding of regolith formation.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"444 ","pages":"Article 116790"},"PeriodicalIF":3.0,"publicationDate":"2025-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145048157","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characterization of the surface of the Ina irregular Mare patch: A synthesis of lunar optical data, including Danuri polarimetric measurements","authors":"Yuriy Shkuratov ,&nbsp;Vadym Kaydash ,&nbsp;James Head ,&nbsp;Kilho Baek ,&nbsp;Sungsoo S. Kim ,&nbsp;Nickolay Opanasenko ,&nbsp;Yehor Surkov ,&nbsp;Minsup Jeong ,&nbsp;Young-Jun Choi ,&nbsp;Chae Kyung Sim ,&nbsp;Dukhang Lee ,&nbsp;Michael Kreslavsky ,&nbsp;William H. Farrand ,&nbsp;Caleb Fassett ,&nbsp;Gorden Videen","doi":"10.1016/j.icarus.2025.116796","DOIUrl":"10.1016/j.icarus.2025.116796","url":null,"abstract":"<div><div>Optical measurements of the enigmatic Ina lunar Irregular Mare Patch (IMP) summit pit crater show that the composition (FeO and TiO₂ content) and degree of optical maturity (<em>OMAT</em>) are almost identical for the flat-topped mounds and the surrounding pit crater flank areas of the Ina formation. In contrast, the Ina rough floor unit and the flank regions are very different. The same relationships are observed when using PolCam polarimetric data of the <em>Danuri</em> mission, as well as Earth-based telescope measurements. In particular, with optical data the rough floor areas display a higher abundance of TiO₂ and larger mean particle size. Chandrayaan 1 M³ spectral data for Ina reveal a locally more intensive absorption band near 3<span><math><mi>μm</mi></math></span>, indicating an excess of H₂O/OH⁻ compounds. Using these data, we analyze different models for the formation of the Ina pit crater, finding that the roof-collapse scenario appears most consistent with the observations. In this scenario, ancient basalt eruptions from the proto-Ina vent created the shield volcano. Next, the lava lake in the volcanic pit crater cooled and solidified from the upper surface downward, and roofed over, while the underlying lava lake, assisted by magmatic degassing, subsequently drained into the vent below, forming a void, with preferentially cooled vertical pillars supporting the roof. Over the next several billion years, detailed traces of the roofing event were obscured by regolith-formation processes. Recently, in the last tens of millions of years, the ancient, roofed void collapsed due to an impact and associate impact/tectonic seismic activity. The seismic effects, which accompany the formation of the crater Tycho, are considered as a feasible cause of the collapse. During this collapse, many of the superposed craters, and a portion of the regolith on the mound surfaces were lost. The rough floor terrain formed simultaneously from the collapse of blocks, debris, and shedding of regolith of the roof materials fallen in voids. The terrain were formed around groups of the pillars. These flat-topped mounds are interpreted as surviving roof remnants. New craters were then formed, but their density distribution is much lower than on the surrounding Ina shield volcano, indicating the recent age of the collapse event. This model explains the similarity of the composition and maturity of the regolith of the mounds and surrounding areas, as well as difference between the composition of the mounds and rough floor terrain. This recent roof-collapse model is also in agreement with the excess of H₂O/OH⁻ compounds in the rough floor terrain that are considered to be young. The young age of the rough floor terrain is consistent with the photometric and polarimetric data that predict undeveloped fairy-castle microstructure and the availability of large particles in the regolit","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"444 ","pages":"Article 116796"},"PeriodicalIF":3.0,"publicationDate":"2025-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145048158","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Morphology-constrained pixel-resolution topographic reconstruction of impact craters from single-imagery","authors":"Wai Chung Liu ,&nbsp;Min Ding ,&nbsp;Luyuan Xu ,&nbsp;Meng-Hua Zhu","doi":"10.1016/j.icarus.2025.116798","DOIUrl":"10.1016/j.icarus.2025.116798","url":null,"abstract":"<div><div>Impact craters provides critical insight into the geological evolution of solid solar system bodies, and accurate 3D topography is required to quantify their morphology. To this end, single-image methods (e.g., photoclinometry) that reconstructs topography from one image are gaining attention for their significantly better spatial resolution and coverage. They are particularly useful for planetary bodies with limited observations, such as asteroids and icy moons visited by flybys. However, single-image techniques suffer from spatially uneven uncertainties which may introduce significant systematic bias to the resulted crater geometry.</div><div>Therefore, we developed a crater-morphology-constrained photoclinometric method for generating reliable, unbiased, pixel-resolution crater 3D models from single-imagery. The systematic bias are handled by considering a crater's symmetrical properties. We validated the method using ∼200 lunar craters (<em>D</em> = 50-1100 m) automatically detected from the LROCNAC images, with stereo NACDTMs as ground truth. The new method achieved a crater depth error of about 9 %–18 % and discrepancies in crater depth retrieval due to systematic bias were below 2 %, outperforming other single-image methods that have a depth error of ∼20 % and a systematic bias of ∼15 % for the same condition. The performance behavior and limitations of the new technique were extensively discussed. In addition, we also presented demonstrations on applications to Mercury and Ganymede craters.</div><div>The intended applications of this work include reliable 3D mapping of craters on icy moons, Earth's Moon and other solar system bodies. This work is also the first recent attempt to systematically assess single-image methods in retrieving crater depth. Hence crater researchers can refer to our assessment results when using single-image techniques in their studies to obtain crater morphological parameters.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"444 ","pages":"Article 116798"},"PeriodicalIF":3.0,"publicationDate":"2025-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145048224","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Boulder degradation and exhumation at the rim of lunar kilometer-scale craters","authors":"Yuan Li ,&nbsp;A.T. Basilevsky ,&nbsp;Wing-Huen Ip","doi":"10.1016/j.icarus.2025.116804","DOIUrl":"10.1016/j.icarus.2025.116804","url":null,"abstract":"<div><div>Previous studies have indicated that boulder exhumation results in the longstanding presence of surface boulders at crater rims throughout the lifetime of lunar maria. In our theoretical analysis, we suggest that mass-wasting processes and the negative balance zone effect of surface material movement play major roles in the exposure of shallow surface boulders. Given the numerous craters of various sizes and ages on the Moon, this specific subpopulation constitutes a considerable part of lunar surface boulders. Therefore, we conducted detailed observations of the topography and morphology of these boulder areas, and performed a boulder (&gt; 6 m) statistical analysis to better understand the degradation processes and underlying exhumation mechanisms of these boulders.</div><div>Herein, we examined high boulder abundance areas at the rims of 79 km-scale lunar craters, whose ages are uniformly distributed across the estimated survival timescale of most meter-sized boulders (∼300 Ma). Optical image analysis did not reveal distinct topographic features indicative of regolith movement. The observed boulders, if not exogenous, have likely remained in proximity to their original emplacement and experienced minimal subsequent displacement. In these areas, boulder degradation is primarily governed by impact-induced erosion and thermal fatigue, gradually declining both boulder number density and maximum size over time. However, this overall trend is complicated by the continual exhumation of shallow subsurface boulders, which replenishes the surface population. This is supported by the longer estimated boulder half-life in our study areas (∼100 Ma), compared to previously reported values for meter-sized boulders (40–80 Ma), and by the presence of large boulders at some older craters that are comparable in size to those at younger ones. We propose that in older craters, the negative balance zone effect may dominate the exhumation process, and that boulder degradation and exhumation may reach a quasi-equilibrium state, sustaining a stable surface boulder population over the geological history of the lunar maria.</div><div>The observations and interpretations of this study provide a unique perspective on the understanding of boulder evolution processes on the lunar surface. Additionally, this study also provides useful insights for future lunar sampling campaigns.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"444 ","pages":"Article 116804"},"PeriodicalIF":3.0,"publicationDate":"2025-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145048160","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}