Pub Date : 2026-01-22DOI: 10.1016/j.icarus.2026.116967
Márton Mester , R. John Wilson , Melinda A. Kahre
We investigate the influence of radiatively active water–ice clouds on tropical wave variability in Mars’ Aphelion Cloud Belt using Mars general circulation model simulations. Wavenumber–frequency spectral and empirical orthogonal function analyses reveal four primary categories of variability: fast eastward- and westward-propagating waves, slow eastward and westward oscillations associated with the Tropical Cloud Oscillation (TCO), and the diurnal westward-propagating wavenumber-1 tide (DW1). When water–ice clouds are radiatively active, the spectrum of tropical variability is dominated by a 13-sol, eastward-propagating wavenumber-1 mode and a 7-sol, westward-propagating wavenumber-2 mode. Both exhibit vertically coherent, quasi-barotropic structures in the cloud field but distinct baroclinic signatures in temperature, indicating partial dynamical coupling between thermal and microphysical variability. By contrast, simulations without radiatively active clouds display more distinct Kelvin and Rossby wave-like bands and qualitatively different spatial structures among slow waves. Radiative feedbacks redistribute energy and concentrate the spectral distribution to a discrete set of wave modes, and promote vertically extended, hemispherically coupled wave modes. The slow TCO-related variability is particularly sensitive to cloud radiative effects. With radiatively active clouds, the long-period spectral wave band forms a robust three-state oscillation involving alternating cloudiness over Tharsis and Syrtis Major — consistent with observations. However, in the absence of radiative feedbacks, the variability collapses into a single, slowly propagating mode confined to Tharsis. These results demonstrate that radiatively active water–ice clouds fundamentally reshape the spectrum and structure of Martian tropical waves. By introducing vertically distributed diabatic heating and enhancing thermal–microphysical coupling, cloud radiative effects sustain the large-scale, seasonally modulated oscillations that characterize the tropical cloud regime on Mars.
{"title":"Radiatively coupled equatorial waves in Mars’ Aphelion Cloud Belt: Wavenumber–frequency analysis in Mars GCM simulations","authors":"Márton Mester , R. John Wilson , Melinda A. Kahre","doi":"10.1016/j.icarus.2026.116967","DOIUrl":"10.1016/j.icarus.2026.116967","url":null,"abstract":"<div><div>We investigate the influence of radiatively active water–ice clouds on tropical wave variability in Mars’ Aphelion Cloud Belt using Mars general circulation model simulations. Wavenumber–frequency spectral and empirical orthogonal function analyses reveal four primary categories of variability: fast eastward- and westward-propagating waves, slow eastward and westward oscillations associated with the Tropical Cloud Oscillation (TCO), and the diurnal westward-propagating wavenumber-1 tide (DW1). When water–ice clouds are radiatively active, the spectrum of tropical variability is dominated by a 13-sol, eastward-propagating wavenumber-1 mode and a 7-sol, westward-propagating wavenumber-2 mode. Both exhibit vertically coherent, quasi-barotropic structures in the cloud field but distinct baroclinic signatures in temperature, indicating partial dynamical coupling between thermal and microphysical variability. By contrast, simulations without radiatively active clouds display more distinct Kelvin and Rossby wave-like bands and qualitatively different spatial structures among slow waves. Radiative feedbacks redistribute energy and concentrate the spectral distribution to a discrete set of wave modes, and promote vertically extended, hemispherically coupled wave modes. The slow TCO-related variability is particularly sensitive to cloud radiative effects. With radiatively active clouds, the long-period spectral wave band forms a robust three-state oscillation involving alternating cloudiness over Tharsis and Syrtis Major — consistent with observations. However, in the absence of radiative feedbacks, the variability collapses into a single, slowly propagating mode confined to Tharsis. These results demonstrate that radiatively active water–ice clouds fundamentally reshape the spectrum and structure of Martian tropical waves. By introducing vertically distributed diabatic heating and enhancing thermal–microphysical coupling, cloud radiative effects sustain the large-scale, seasonally modulated oscillations that characterize the tropical cloud regime on Mars.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"449 ","pages":"Article 116967"},"PeriodicalIF":3.0,"publicationDate":"2026-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035953","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}
Pub Date : 2026-01-21DOI: 10.1016/j.icarus.2026.116949
Pascal Rannou , Bruno de Batz de Trenquelléon , Sébastien Rodriguez , Benoît Seignovert
The Cassini orbiter around Saturn monitored Titan with multiple instruments 13 years, between 2004 to 2017. This is about half of a Titan year and this period included a major seasonal change at the North Spring Equinox (NSE) in 2009 that could be observed. The Visual and Infrared Mapping Spectrometer (VIMS) onboard Cassini produced a large amount of observations of Titan generally presented under the form of spectro-images. The observations with the IR part of VIMS detector are taken in a spectral range between 0.88 to and with a resolving power between R= = 120 and 180. The spatial resolution of the images depends on the observation and is few hundreds of meters at the best. In this study, we retrieved the distribution of the photochemical haze (above 80 km) and the condensate mist layer (below 80 km) as a function of latitude, altitude, and tile throughout the Cassini era. We found a haze latitudinal distribution with an extinction increasing from the south to the north at the beginning of the Cassini mission. The distribution evolved around the North Spring Equinox and a turnover was completely achieved at the end of the Cassini mission. This evolution is linked to the stratospheric circulation that blows from the summer hemisphere to the winter polar region. The latitudinal distribution of the mist layer evolves differently than the haze distribution because it depends on both the circulation pattern in the low atmosphere and on the conditions of condensation for several species. The distribution of the mist layer is also modulated with the seasons, but always increases from the equator and inter-tropical latitude band to the poles.
These results yield a quantitative description of the aerosol layer on Titan and its seasonal evolution. This has been compared with previous works and with the output of the Titan Planetary Climate Model. Producing such results is quite important to constrain climate models. In return, we expect from these climate models to be helpful in fully understanding the meaning of our results and more generally in characterizing Titan’s climate.
{"title":"Seasonal variations of Titan’s haze and mist layers monitored by VIMS-IR onboard Cassini","authors":"Pascal Rannou , Bruno de Batz de Trenquelléon , Sébastien Rodriguez , Benoît Seignovert","doi":"10.1016/j.icarus.2026.116949","DOIUrl":"10.1016/j.icarus.2026.116949","url":null,"abstract":"<div><div>The Cassini orbiter around Saturn monitored Titan with multiple instruments 13 years, between 2004 to 2017. This is about half of a Titan year and this period included a major seasonal change at the North Spring Equinox (NSE) in 2009 that could be observed. The Visual and Infrared Mapping Spectrometer (VIMS) onboard Cassini produced a large amount of observations of Titan generally presented under the form of spectro-images. The observations with the IR part of VIMS detector are taken in a spectral range between 0.88 to <span><math><mrow><mn>5</mn><mo>.</mo><mn>12</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span> and with a resolving power between R= <span><math><mrow><mi>λ</mi><mo>/</mo><mi>Δ</mi><mi>λ</mi></mrow></math></span> = 120 and 180. The spatial resolution of the images depends on the observation and is few hundreds of meters at the best. In this study, we retrieved the distribution of the photochemical haze (above 80 km) and the condensate mist layer (below 80 km) as a function of latitude, altitude, and tile throughout the Cassini era. We found a haze latitudinal distribution with an extinction increasing from the south to the north at the beginning of the Cassini mission. The distribution evolved around the North Spring Equinox and a turnover was completely achieved at the end of the Cassini mission. This evolution is linked to the stratospheric circulation that blows from the summer hemisphere to the winter polar region. The latitudinal distribution of the mist layer evolves differently than the haze distribution because it depends on both the circulation pattern in the low atmosphere and on the conditions of condensation for several species. The distribution of the mist layer is also modulated with the seasons, but always increases from the equator and inter-tropical latitude band to the poles.</div><div>These results yield a quantitative description of the aerosol layer on Titan and its seasonal evolution. This has been compared with previous works and with the output of the Titan Planetary Climate Model. Producing such results is quite important to constrain climate models. In return, we expect from these climate models to be helpful in fully understanding the meaning of our results and more generally in characterizing Titan’s climate.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"450 ","pages":"Article 116949"},"PeriodicalIF":3.0,"publicationDate":"2026-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146070909","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}
Pub Date : 2026-01-21DOI: 10.1016/j.icarus.2026.116965
B.G. Rider-Stokes , F.A. Davies , T.H. Burbine , E. MacLennan , R.C. Greenwood , S.L. Jackson , M. Anand , D. Sheikh , M.M. Grady
Brachinite meteorites are typically linked to the olivine-rich A-type asteroids. In this study, however, they appear to exhibit unexpected spectral diversity. Spectroscopic analysis of seven meteorites from the brachinite clan reveals two distinct populations in band parameters, overlapping with both the A-type and S-complex asteroids. This dual association shows that a single meteorite group can originate from multiple asteroid taxonomies. Notably, one S-complex-like specimen, Northwest Africa (NWA) 14,635, displays band parameters similar to those of asteroid (65803) Didymos, the target of the European Space Agency's (ESA) ongoing Hera mission. These results underscore the value of spectroscopic characterization of poorly understood meteorite groups and identifying potential analogs that are highly relevant for current and future mission planning.
{"title":"Crossing boundaries: Brachinites and their diverse asteroidal origins","authors":"B.G. Rider-Stokes , F.A. Davies , T.H. Burbine , E. MacLennan , R.C. Greenwood , S.L. Jackson , M. Anand , D. Sheikh , M.M. Grady","doi":"10.1016/j.icarus.2026.116965","DOIUrl":"10.1016/j.icarus.2026.116965","url":null,"abstract":"<div><div>Brachinite meteorites are typically linked to the olivine-rich A-type asteroids. In this study, however, they appear to exhibit unexpected spectral diversity. Spectroscopic analysis of seven meteorites from the brachinite clan reveals two distinct populations in band parameters, overlapping with both the A-type and S-complex asteroids. This dual association shows that a single meteorite group can originate from multiple asteroid taxonomies. Notably, one S-complex-like specimen, Northwest Africa (NWA) 14,635, displays band parameters similar to those of asteroid (65803) Didymos, the target of the European Space Agency's (ESA) ongoing Hera mission. These results underscore the value of spectroscopic characterization of poorly understood meteorite groups and identifying potential analogs that are highly relevant for current and future mission planning.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"449 ","pages":"Article 116965"},"PeriodicalIF":3.0,"publicationDate":"2026-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035947","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}
Pub Date : 2026-01-20DOI: 10.1016/j.icarus.2026.116964
Veronika A. Korneyeva , Jason M. Pearl , Kathryn M. Kumamoto , J. Michael Owen , Cody D. Raskin , Megan B. Syal , Nicholaus J. Parziale , Stuart J. Laurence
Contemporary discussions of planetary defense involve analyzing the risks posed by smaller sized, 20 to 200 m diameter, asteroids which are capable of breaking up in the atmosphere and generating a blast wave. Consequence assessments for this size class of asteroids are performed through fast-running analytic or semi-analytic models which are informed by high-fidelity hydrocode simulations of asteroid entry and breakup. However, insufficient historical data necessitates validating the independent physical processes which dominate airburst events. The Fluid Solid Interface Smoothed Particle Hydrodynamics solver was previously used by Pearl et al. in 2023 to model the Chelyabinsk airburst and is used here to perform a series of validation simulations. The first effort involves modeling a cylinder in a hypersonic flow and comparing the bow shock geometry to that predicted by analytic theory. The second effort involves modeling the separation of two spherical bodies in supersonic flow and validating against experimental footage. Combined, these exercises demonstrate the ability of the code to model the flight-path of interacting solid bodies in a hypersonic flow.
{"title":"Validation of SPH code Spheral to model interacting solid bodies in a supersonic flow","authors":"Veronika A. Korneyeva , Jason M. Pearl , Kathryn M. Kumamoto , J. Michael Owen , Cody D. Raskin , Megan B. Syal , Nicholaus J. Parziale , Stuart J. Laurence","doi":"10.1016/j.icarus.2026.116964","DOIUrl":"10.1016/j.icarus.2026.116964","url":null,"abstract":"<div><div>Contemporary discussions of planetary defense involve analyzing the risks posed by smaller sized, 20 to 200 m diameter, asteroids which are capable of breaking up in the atmosphere and generating a blast wave. Consequence assessments for this size class of asteroids are performed through fast-running analytic or semi-analytic models which are informed by high-fidelity hydrocode simulations of asteroid entry and breakup. However, insufficient historical data necessitates validating the independent physical processes which dominate airburst events. The Fluid Solid Interface Smoothed Particle Hydrodynamics solver was previously used by Pearl et al. in 2023 to model the Chelyabinsk airburst and is used here to perform a series of validation simulations. The first effort involves modeling a cylinder in a hypersonic flow and comparing the bow shock geometry to that predicted by analytic theory. The second effort involves modeling the separation of two spherical bodies in supersonic flow and validating against experimental footage. Combined, these exercises demonstrate the ability of the code to model the flight-path of interacting solid bodies in a hypersonic flow.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"449 ","pages":"Article 116964"},"PeriodicalIF":3.0,"publicationDate":"2026-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074892","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}
The Physics-Informed Extreme Learning Machine (PIELM) is a single-hidden-layer feedforward neural network. It integrates the rapid training capability of Extreme Learning Machines (ELM) with the physics-informed strength of Physics-Informed Neural Networks (PINN), ensuring solutions consistent with physical laws and measurements. This synergy makes PIELM well-suited for solving the complex orbit determination problem. In this study, we extended the PIELM framework to Near-Earth Asteroid (NEA) orbit determination, proposing a comprehensive and operational strategy. Our approach is specifically designed to account for unique NEA characteristics, notably incorporating light-time correction into the measurement model. A statistical analysis using a large number of real NEA observations was conducted to assess PIELM’s accuracy in NEA orbit determination. The results demonstrate that although PIELM’s precision does not yet match the traditional least-squares method, it achieves sufficient accuracy for most scenarios covered in this study. Notably, PIELM does not require any prior orbit guess and demonstrates performance comparable or superior to the classical Laplace method in Initial Orbit Determination (IOD). This capability is vital for NEA discovery and recovery in the upcoming data-intensive survey era.
{"title":"Near-Earth Asteroid orbit determination with Physics-Informed Extreme Learning Machine","authors":"Xiuyu Chen , Kai Tang , Qingfeng Zhang , Zhenliang Tian , Yong Yu","doi":"10.1016/j.icarus.2026.116962","DOIUrl":"10.1016/j.icarus.2026.116962","url":null,"abstract":"<div><div>The Physics-Informed Extreme Learning Machine (PIELM) is a single-hidden-layer feedforward neural network. It integrates the rapid training capability of Extreme Learning Machines (ELM) with the physics-informed strength of Physics-Informed Neural Networks (PINN), ensuring solutions consistent with physical laws and measurements. This synergy makes PIELM well-suited for solving the complex orbit determination problem. In this study, we extended the PIELM framework to Near-Earth Asteroid (NEA) orbit determination, proposing a comprehensive and operational strategy. Our approach is specifically designed to account for unique NEA characteristics, notably incorporating light-time correction into the measurement model. A statistical analysis using a large number of real NEA observations was conducted to assess PIELM’s accuracy in NEA orbit determination. The results demonstrate that although PIELM’s precision does not yet match the traditional least-squares method, it achieves sufficient accuracy for most scenarios covered in this study. Notably, PIELM does not require any prior orbit guess and demonstrates performance comparable or superior to the classical Laplace method in Initial Orbit Determination (IOD). This capability is vital for NEA discovery and recovery in the upcoming data-intensive survey era.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"449 ","pages":"Article 116962"},"PeriodicalIF":3.0,"publicationDate":"2026-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074887","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}
Pub Date : 2026-01-18DOI: 10.1016/j.icarus.2026.116960
Edoardo Santero Mormile , Giuseppe Mitri
Determining the internal structure of planetary bodies from gravitational observations is a key challenge in planetary geophysics. Traditional gravity inversion methods suffer from non-uniqueness due to trade-offs between mass distribution and depth, limiting their ability to resolve internal layering. We present SynthGen, a forward-modelling code developed to simulate the gravitational response of planetary bodies using parametric, multi-layer interior models without any a priori assumption, like the hydrostatic equilibrium. SynthGen calculates gravitational potential, Free-Air, and Bouguer anomalies through spherical harmonic expansions, leveraging the SHTools library (Wieczorek and Meschede, 2018). It accommodates a wide variety of internal configurations, including homogeneous layers with user-defined densities, thicknesses, and topographic geometries of internal interfaces, such as spherical, ellipsoidal, random, or Bouguer anomaly-derived interfaces. The code can be used both predictively and diagnostically: about the latter, SynthGen performs parameter-space exploration constrained by total mass, moment of inertia, and shape, identifying best-fit interior models by minimising the misfit between observed and synthetic gravity fields using combined statistical metrics. We apply SynthGen to Mercury, using the HgM009 gravity model derived from MESSENGER data (Genova et al., 2023), and recover crustal thickness and core parameters consistent with recent independent geophysical estimates. In predictive mode, SynthGen generates synthetic gravity fields for planetary bodies where gravity data are not available or are still limited in resolution, such as Ganymede. These simulations can support the planning and optimisation of space missions. By integrating physical constraints, statistical validation, and flexibility in model design, SynthGen offers a robust platform for planetary interior studies, constraining interior structures from gravity measurements across a broad range of Solar System bodies.
从引力观测中确定行星体的内部结构是行星地球物理学的一个关键挑战。传统的重力反演方法由于质量分布和深度之间的权衡而存在非唯一性，限制了其解决内部分层的能力。我们介绍了SynthGen，这是一个正向建模代码，用于模拟行星体的引力响应，使用参数化的多层内部模型，而不需要任何先验假设，如流体静力平衡。SynthGen利用SHTools库（Wieczorek和Meschede， 2018），通过球谐展开计算重力势、Free-Air和布格异常。它可以容纳各种各样的内部配置，包括具有用户定义的密度、厚度和内部界面的地形几何形状的均匀层，例如球面、椭球面、随机或布格异常派生的界面。该代码既可用于预测，也可用于诊断：对于后者，SynthGen执行受总质量、惯性矩和形状约束的参数空间探索，通过使用组合统计度量最小化观测和合成重力场之间的不拟合来识别最适合的内部模型。我们将SynthGen应用于水星，使用从MESSENGER数据中导出的HgM009重力模型（Genova et al., 2023），并恢复了与最近独立地球物理估计一致的地壳厚度和核心参数。在预测模式下，SynthGen为无法获得重力数据或分辨率仍然有限的行星体（如Ganymede）生成合成重力场。这些模拟可以支持空间任务的规划和优化。通过整合物理约束、统计验证和模型设计的灵活性，SynthGen为行星内部研究提供了一个强大的平台，限制了太阳系大范围天体重力测量的内部结构。
{"title":"SynthGen: A gravity field simulator for planetary interior modelling","authors":"Edoardo Santero Mormile , Giuseppe Mitri","doi":"10.1016/j.icarus.2026.116960","DOIUrl":"10.1016/j.icarus.2026.116960","url":null,"abstract":"<div><div>Determining the internal structure of planetary bodies from gravitational observations is a key challenge in planetary geophysics. Traditional gravity inversion methods suffer from non-uniqueness due to trade-offs between mass distribution and depth, limiting their ability to resolve internal layering. We present <em>SynthGen</em>, a forward-modelling code developed to simulate the gravitational response of planetary bodies using parametric, multi-layer interior models without any a priori assumption, like the hydrostatic equilibrium. <em>SynthGen</em> calculates gravitational potential, Free-Air, and Bouguer anomalies through spherical harmonic expansions, leveraging the <em>SHTools</em> library (Wieczorek and Meschede, 2018). It accommodates a wide variety of internal configurations, including homogeneous layers with user-defined densities, thicknesses, and topographic geometries of internal interfaces, such as spherical, ellipsoidal, random, or Bouguer anomaly-derived interfaces. The code can be used both predictively and diagnostically: about the latter, <em>SynthGen</em> performs parameter-space exploration constrained by total mass, moment of inertia, and shape, identifying best-fit interior models by minimising the misfit between observed and synthetic gravity fields using combined statistical metrics. We apply <em>SynthGen</em> to Mercury, using the HgM009 gravity model derived from MESSENGER data (Genova et al., 2023), and recover crustal thickness and core parameters consistent with recent independent geophysical estimates. In predictive mode, <em>SynthGen</em> generates synthetic gravity fields for planetary bodies where gravity data are not available or are still limited in resolution, such as Ganymede. These simulations can support the planning and optimisation of space missions. By integrating physical constraints, statistical validation, and flexibility in model design, <em>SynthGen</em> offers a robust platform for planetary interior studies, constraining interior structures from gravity measurements across a broad range of Solar System bodies.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"449 ","pages":"Article 116960"},"PeriodicalIF":3.0,"publicationDate":"2026-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035949","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}
Pub Date : 2026-01-17DOI: 10.1016/j.icarus.2026.116959
Ian C. Matheson , Renu Malhotra
Hilda-group asteroids librate in Jupiter’s interior 3:2 mean motion resonance. We estimate that the Hilda group is observationally complete up to absolute magnitude . This provides a statistically useful sample of thousands of resonant objects, all within a narrow range of semi-major axes, to compare with theoretical expectations of their orbital distribution from dynamical theory. We use von Mises–Fisher statistics to calculate the sample mean planes and mean plane uncertainties for the Hilda group and its Hilda, Schubart, and Potomac collisional subfamilies. Although Laplace–Lagrange linear secular theory is considered inapplicable within mean motion resonances, we find that the Laplace plane and the orbital plane of Jupiter are both statistically indistinguishable from the sample mean plane of the Hildas. In future work, we intend to extend this investigation to resonant populations in the Kuiper belt so as to further test the validity of Laplace–Lagrange linear secular theory for the mean planes of resonant populations.
{"title":"On the forced orbital plane of the Hilda asteroids","authors":"Ian C. Matheson , Renu Malhotra","doi":"10.1016/j.icarus.2026.116959","DOIUrl":"10.1016/j.icarus.2026.116959","url":null,"abstract":"<div><div>Hilda-group asteroids librate in Jupiter’s interior 3:2 mean motion resonance. We estimate that the Hilda group is observationally complete up to absolute magnitude <span><math><mrow><mi>H</mi><mo>≤</mo><mn>16</mn><mo>.</mo><mn>3</mn></mrow></math></span>. This provides a statistically useful sample of thousands of resonant objects, all within a narrow range of semi-major axes, to compare with theoretical expectations of their orbital distribution from dynamical theory. We use von Mises–Fisher statistics to calculate the sample mean planes and mean plane uncertainties for the Hilda group and its Hilda, Schubart, and Potomac collisional subfamilies. Although Laplace–Lagrange linear secular theory is considered inapplicable within mean motion resonances, we find that the Laplace plane and the orbital plane of Jupiter are both statistically indistinguishable from the sample mean plane of the Hildas. In future work, we intend to extend this investigation to resonant populations in the Kuiper belt so as to further test the validity of Laplace–Lagrange linear secular theory for the mean planes of resonant populations.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"449 ","pages":"Article 116959"},"PeriodicalIF":3.0,"publicationDate":"2026-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035952","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}
Pub Date : 2026-01-17DOI: 10.1016/j.icarus.2026.116939
Albino Carbognani , Marco Fenucci , Toni Santana-Ros , Clara E. Martínez-Vázquez , Marco Micheli
We analyse the association between the NEAs 2021 PH27 and 2025 GN1, which share similar heliocentric Keplerian elements and the same taxonomic classification. First, we confirm the spectral similarity by getting independent colours measurements of 2025 GN1 and confirming that they are both X-type. From numerical integration of the orbits up to 100 kyr in the past, taking into account relativistic corrections, we found that the two asteroids experienced five similar flybys with Venus, but none of them were closer than the Roche limit. The perihelion distance also reached values between 0.1 and 0.08 au about 17/21 kyr and 45/48 kyr ago, but still well outside the Roche limit with the Sun. So, the origin of the pair by tidal disruption of a progenitor rubble-pile asteroid appears unlikely. On the other hand, we found periods lasting several thousand years where the perihelion was below 0.1 au, and this can lead to thermal fracturing of the surface. We found that the rotation period of the primary and the mass ratio secondary/primary make the pair indistinguishable from the binary systems known among the NEAs, and the YORP effect can double the rotation period of 2021 PH27 in kyr. So it is plausible that the pair was formed by the rotational disintegration of a rubble-pile asteroid due to anisotropic gas emission or the YORP effect, which formed a binary system that later dissolved due to the internal dynamics of the pair. We are unable to give a value for the separation age; we can only say that it occurred more than 10.5 kyr ago and may have occurred between 17/21 kyr ago during the last and longer phase of lower perihelion distance. In this scenario, little meteoroids released in space due to the fragmentation event are still near the pair’s orbit and can generate a meteor shower in Venus’ atmosphere.
{"title":"Investigation of the dynamics and origin of the NEA pair 2021 PH27 and 2025 GN1","authors":"Albino Carbognani , Marco Fenucci , Toni Santana-Ros , Clara E. Martínez-Vázquez , Marco Micheli","doi":"10.1016/j.icarus.2026.116939","DOIUrl":"10.1016/j.icarus.2026.116939","url":null,"abstract":"<div><div>We analyse the association between the NEAs 2021 PH27 and 2025 GN1, which share similar heliocentric Keplerian elements and the same taxonomic classification. First, we confirm the spectral similarity by getting independent colours measurements of 2025 GN1 and confirming that they are both X-type. From numerical integration of the orbits up to 100 kyr in the past, taking into account relativistic corrections, we found that the two asteroids experienced five similar flybys with Venus, but none of them were closer than the Roche limit. The perihelion distance also reached values between 0.1 and 0.08 au about 17/21 kyr and 45/48 kyr ago, but still well outside the Roche limit with the Sun. So, the origin of the pair by tidal disruption of a progenitor rubble-pile asteroid appears unlikely. On the other hand, we found periods lasting several thousand years where the perihelion was below 0.1 au, and this can lead to thermal fracturing of the surface. We found that the rotation period of the primary and the mass ratio secondary/primary make the pair indistinguishable from the binary systems known among the NEAs, and the YORP effect can double the rotation period of 2021 PH27 in <span><math><mrow><mn>150</mn><mo>±</mo><mn>50</mn></mrow></math></span> kyr. So it is plausible that the pair was formed by the rotational disintegration of a rubble-pile asteroid due to anisotropic gas emission or the YORP effect, which formed a binary system that later dissolved due to the internal dynamics of the pair. We are unable to give a value for the separation age; we can only say that it occurred more than 10.5 kyr ago and may have occurred between 17/21 kyr ago during the last and longer phase of lower perihelion distance. In this scenario, little meteoroids released in space due to the fragmentation event are still near the pair’s orbit and can generate a meteor shower in Venus’ atmosphere.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"449 ","pages":"Article 116939"},"PeriodicalIF":3.0,"publicationDate":"2026-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035954","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}
Pub Date : 2026-01-16DOI: 10.1016/j.icarus.2026.116935
Peter Howard Cadogan
<div><div>An automated system for counting very small lunar craters has been applied to many locations on the Moon, including some on the far side and others at high latitudes. Many of these locations are on level mare terrain, but a few highland areas and the ejecta blankets and impact melts of several Copernican-age craters have been investigated.</div><div>Craters smaller than 50 m in diameter can be no more that a few hundred million years old, so are of little use for dating more ancient lunar features. However, in this size range, significant differences in crater densities exist across sites, implying that recent surface activity must have occurred. So a simulation model has been developed to investigate these processes further.</div><div>A 1 Ma crater production function has been developed, based of the size distribution of craters on the ejecta blanket of the young crater Giordano Bruno, assuming its age to be 10 Ma. This function is consistent with predictions based on the meteoroid flux at the surface of the Moon. Using a simple model for obliteration and topographic diffusion, the primary mechanisms by which small craters are thought to be erased and eroded, simulated distributions have been successfully matched to measured densities. The results indicate that several locations on the Moon must have been wholly or partially resurfaced within the last 100 Ma.</div><div>The simulation model has also been used to confirm published formation ages for Tycho, North Ray and Cone craters. Several other large young craters (including Necho, Dawes, Lalande, Tharp, Messier, Messier A, Euclides C, Furnerius A and Proclus) have been confidently dated, where necessary making adjustments for the predicted variation in meteoroid flux between the apex and antapex of the Moon's orbit around the Earth. Densities of small craters on a Tycho impact melt are much lower than those on its ejecta blanket. These craters last for much longer, enabling impact melts at older craters (such as King, Kepler and Aristarchus) to be estimated more precisely than was possible from their ejecta blankets.</div><div>Simulation results confirm that erosion and obliteration are the primary factors responsible for crater destruction, but blanketing by ejecta from larger impacts and seismic shaking have clearly been effective at some sites. Seismic shaking during the excavation of km-sized craters may erase nearby small craters prior to ejecta blanket deposition. Self-secondaries are visibly different from primaries and are typically found closer to crater rims. There is no obvious need to invoke self-secondaries to explain high crater densities at the smallest sizes.</div><div>At many sites, crater densities have clearly reached equilibrium. This enables lifetimes of craters smaller than 30 m in diameter to be determined, the results being consistent with published values. Equilibrium densities can vary significantly between sites, presumably due to the different regolith pro
{"title":"Automated precision counting of very small lunar craters – A simulation study","authors":"Peter Howard Cadogan","doi":"10.1016/j.icarus.2026.116935","DOIUrl":"10.1016/j.icarus.2026.116935","url":null,"abstract":"<div><div>An automated system for counting very small lunar craters has been applied to many locations on the Moon, including some on the far side and others at high latitudes. Many of these locations are on level mare terrain, but a few highland areas and the ejecta blankets and impact melts of several Copernican-age craters have been investigated.</div><div>Craters smaller than 50 m in diameter can be no more that a few hundred million years old, so are of little use for dating more ancient lunar features. However, in this size range, significant differences in crater densities exist across sites, implying that recent surface activity must have occurred. So a simulation model has been developed to investigate these processes further.</div><div>A 1 Ma crater production function has been developed, based of the size distribution of craters on the ejecta blanket of the young crater Giordano Bruno, assuming its age to be 10 Ma. This function is consistent with predictions based on the meteoroid flux at the surface of the Moon. Using a simple model for obliteration and topographic diffusion, the primary mechanisms by which small craters are thought to be erased and eroded, simulated distributions have been successfully matched to measured densities. The results indicate that several locations on the Moon must have been wholly or partially resurfaced within the last 100 Ma.</div><div>The simulation model has also been used to confirm published formation ages for Tycho, North Ray and Cone craters. Several other large young craters (including Necho, Dawes, Lalande, Tharp, Messier, Messier A, Euclides C, Furnerius A and Proclus) have been confidently dated, where necessary making adjustments for the predicted variation in meteoroid flux between the apex and antapex of the Moon's orbit around the Earth. Densities of small craters on a Tycho impact melt are much lower than those on its ejecta blanket. These craters last for much longer, enabling impact melts at older craters (such as King, Kepler and Aristarchus) to be estimated more precisely than was possible from their ejecta blankets.</div><div>Simulation results confirm that erosion and obliteration are the primary factors responsible for crater destruction, but blanketing by ejecta from larger impacts and seismic shaking have clearly been effective at some sites. Seismic shaking during the excavation of km-sized craters may erase nearby small craters prior to ejecta blanket deposition. Self-secondaries are visibly different from primaries and are typically found closer to crater rims. There is no obvious need to invoke self-secondaries to explain high crater densities at the smallest sizes.</div><div>At many sites, crater densities have clearly reached equilibrium. This enables lifetimes of craters smaller than 30 m in diameter to be determined, the results being consistent with published values. Equilibrium densities can vary significantly between sites, presumably due to the different regolith pro","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"449 ","pages":"Article 116935"},"PeriodicalIF":3.0,"publicationDate":"2026-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035828","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}
Pub Date : 2026-01-15DOI: 10.1016/j.icarus.2026.116938
L.E. Mc Keown , S. Diniega , M.J. Poston , G. Portyankina , C.J. Hansen , K.-M. Aye , I. Mishra , E. Carey , J.E.C. Scully , S. Piqueux , M. Choukroun
<div><div>The winter/springtime CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> condensation and sublimation cycle is recognized as a cardinal agent of present-day surface change on Mars, and was likely also instrumental in modifying the surface during the recent past. The Kieffer Model postulates that slab ice condenses in winter and sublimates in spring, causing pressurized CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> gas beneath the ice to rush to the surface, forming a ‘zoo’ of features ranging from seasonal plumes, dark fans and spots and the mysterious ‘spiders’ or araneiforms surrounding the Martian south pole. However, the lack of terrestrial analogs or empirical observations of this conceptual process hamper our understanding of how the Martian surface is modified in this way today. In Mc Keown et al. (2024), we presented experiments that simulated all three main stages of the Kieffer model on a <span><math><mo>∼</mo></math></span>1 cm layer of Mars Mojave (regolith) Simulant (MMS) <span><math><mrow><mo><</mo><mn>150</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span>: (i) CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> condensation, (ii) sublimation of CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> ice, and plume, spot and halo formation and (iii) the resultant formation of ‘cracked’ spiders, where interstitial pore ice is sublimated and cracks, preserving patterns in the surrounding regolith. In this paper, we present experiments where CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> condenses on different discrete grain size ranges of regolith: <span><math><mrow><mo><</mo><mn>53</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span>, 75–150<span><math><mrow><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span>, and 180–500 <!--> <span><math><mrow><mi>μ</mi><mi>m</mi></mrow></math></span>, for both ‘dry’ regolith and a water-mixed ‘permafrost’ simulant, and on glass beads 250–355<span><math><mrow><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span>, but forms and sublimates in different ways. We find that CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> diffuses deeper and across a greater area within the regolith pore spaces for finer grain sizes, and the top ice layer grows inward from the sample edges for coarser grains, resulting in finer grains being more prone to ‘cracked’ spider morphologies than coarser grains. Condensation of CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> appears to be affected by thermal properties and circularity of the grains, with rate of ice accumulation on the surface slower on the surface of glass beads and final patterns of ice on the surface differing in appearance from the MMS simulant. Water ice within the pore spaces of the regolith encourages the growth
{"title":"CO2 condensation and sublimation on a range of substrates under simulated mars conditions","authors":"L.E. Mc Keown , S. Diniega , M.J. Poston , G. Portyankina , C.J. Hansen , K.-M. Aye , I. Mishra , E. Carey , J.E.C. Scully , S. Piqueux , M. Choukroun","doi":"10.1016/j.icarus.2026.116938","DOIUrl":"10.1016/j.icarus.2026.116938","url":null,"abstract":"<div><div>The winter/springtime CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> condensation and sublimation cycle is recognized as a cardinal agent of present-day surface change on Mars, and was likely also instrumental in modifying the surface during the recent past. The Kieffer Model postulates that slab ice condenses in winter and sublimates in spring, causing pressurized CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> gas beneath the ice to rush to the surface, forming a ‘zoo’ of features ranging from seasonal plumes, dark fans and spots and the mysterious ‘spiders’ or araneiforms surrounding the Martian south pole. However, the lack of terrestrial analogs or empirical observations of this conceptual process hamper our understanding of how the Martian surface is modified in this way today. In Mc Keown et al. (2024), we presented experiments that simulated all three main stages of the Kieffer model on a <span><math><mo>∼</mo></math></span>1 cm layer of Mars Mojave (regolith) Simulant (MMS) <span><math><mrow><mo><</mo><mn>150</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span>: (i) CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> condensation, (ii) sublimation of CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> ice, and plume, spot and halo formation and (iii) the resultant formation of ‘cracked’ spiders, where interstitial pore ice is sublimated and cracks, preserving patterns in the surrounding regolith. In this paper, we present experiments where CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> condenses on different discrete grain size ranges of regolith: <span><math><mrow><mo><</mo><mn>53</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span>, 75–150<span><math><mrow><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span>, and 180–500 <!--> <span><math><mrow><mi>μ</mi><mi>m</mi></mrow></math></span>, for both ‘dry’ regolith and a water-mixed ‘permafrost’ simulant, and on glass beads 250–355<span><math><mrow><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span>, but forms and sublimates in different ways. We find that CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> diffuses deeper and across a greater area within the regolith pore spaces for finer grain sizes, and the top ice layer grows inward from the sample edges for coarser grains, resulting in finer grains being more prone to ‘cracked’ spider morphologies than coarser grains. Condensation of CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> appears to be affected by thermal properties and circularity of the grains, with rate of ice accumulation on the surface slower on the surface of glass beads and final patterns of ice on the surface differing in appearance from the MMS simulant. Water ice within the pore spaces of the regolith encourages the growth","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"449 ","pages":"Article 116938"},"PeriodicalIF":3.0,"publicationDate":"2026-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035984","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}
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