Pub Date : 2026-01-12DOI: 10.1016/j.icarus.2026.116943
V.F. Peixoto , B.E. Morgado , F.M.W. Tognoli , C. Haslebacher
Europa’s surface is dominated by lineaments that record its tectonic evolution and provide key constraints on ice-shell dynamics. While previous studies have primarily relied on descriptive mapping, here we apply a quantitative framework integrating geometric and topological analyses to characterize fracture networks within high-resolution Galileo SSI mosaics. Lineaments were mapped using the deep learning tool LineaMapper followed by manual refinements in QGIS, producing a consistent dataset across two representative areas located in the leading and trailing hemispheres. From these networks, we computed spacing, density (), and orientation, and performed a topological analysis with the Python package Fractopo. Within the specific areas investigated, the trailing-hemisphere area exhibits higher lineament density, greater node frequency, and more segmented networks, whereas the leading-hemisphere area contains longer, more continuous lineaments with lower connectivity. Orientation patterns further show that longer fractures preferentially align E–W, consistent with tidal stress predictions. These results indicate that fracture networks in the examined sectors are moderately connected and spatially heterogeneous, reflecting local variations in stress and terrain type. The integrated approach presented here provides a quantitative baseline for future studies and will be particularly valuable for interpreting the unprecedented spatial coverage and resolution expected from ESA’s JUICE and NASA’s Europa Clipper missions.
{"title":"Topological analysis of Europa’s fracture networks","authors":"V.F. Peixoto , B.E. Morgado , F.M.W. Tognoli , C. Haslebacher","doi":"10.1016/j.icarus.2026.116943","DOIUrl":"10.1016/j.icarus.2026.116943","url":null,"abstract":"<div><div>Europa’s surface is dominated by lineaments that record its tectonic evolution and provide key constraints on ice-shell dynamics. While previous studies have primarily relied on descriptive mapping, here we apply a quantitative framework integrating geometric and topological analyses to characterize fracture networks within high-resolution Galileo SSI mosaics. Lineaments were mapped using the deep learning tool <span>LineaMapper</span> followed by manual refinements in QGIS, producing a consistent dataset across two representative areas located in the leading and trailing hemispheres. From these networks, we computed spacing, density (<span><math><msub><mrow><mi>P</mi></mrow><mrow><mn>21</mn></mrow></msub></math></span>), and orientation, and performed a topological analysis with the Python package Fractopo. Within the specific areas investigated, the trailing-hemisphere area exhibits higher lineament density, greater node frequency, and more segmented networks, whereas the leading-hemisphere area contains longer, more continuous lineaments with lower connectivity. Orientation patterns further show that longer fractures preferentially align E–W, consistent with tidal stress predictions. These results indicate that fracture networks in the examined sectors are moderately connected and spatially heterogeneous, reflecting local variations in stress and terrain type. The integrated approach presented here provides a quantitative baseline for future studies and will be particularly valuable for interpreting the unprecedented spatial coverage and resolution expected from ESA’s JUICE and NASA’s Europa Clipper missions.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"449 ","pages":"Article 116943"},"PeriodicalIF":3.0,"publicationDate":"2026-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145957674","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 : 2026-01-10DOI: 10.1016/j.icarus.2026.116942
Georgios Tsirvouils , Mikael Granvik , Leonard Schirner , Athanasia Toliou , Jooyeon Geem , Axel Hagermann
Recent models of the near-Earth asteroid population show that asteroids must be super-catastrophically destroyed when they evolve to orbits with perihelion passages well inside of Mercury’s orbit. The heliocentric distances at which the disruptions typically occur are tens of solar radii, which is too far from the Sun for asteroids to be destroyed by sublimation and tidal disruption. The typical disruption distance also appears to be larger for darker asteroids. Here, by carrying out irradiance experiments in vacuum that replicate the conditions in the near-Sun environment, we show that CI meteorite simulants are destroyed within minutes when exposed to the level of solar irradiance encountered at heliocentric distances of up to about 0.2 au. Our results provide an explanation for the scarcity of dark, carbonaceous asteroids with perihelion distances less than 0.2 au, and for the observed mass-loss rate of the asteroid-like object 322P/SOHO 1 assuming its composition is similar to CI carbonaceous chondrites.
{"title":"Instantaneous thermally-driven erosion can explain dearth of dark near-Sun asteroids","authors":"Georgios Tsirvouils , Mikael Granvik , Leonard Schirner , Athanasia Toliou , Jooyeon Geem , Axel Hagermann","doi":"10.1016/j.icarus.2026.116942","DOIUrl":"10.1016/j.icarus.2026.116942","url":null,"abstract":"<div><div>Recent models of the near-Earth asteroid population show that asteroids must be super-catastrophically destroyed when they evolve to orbits with perihelion passages well inside of Mercury’s orbit. The heliocentric distances at which the disruptions typically occur are tens of solar radii, which is too far from the Sun for asteroids to be destroyed by sublimation and tidal disruption. The typical disruption distance also appears to be larger for darker asteroids. Here, by carrying out irradiance experiments in vacuum that replicate the conditions in the near-Sun environment, we show that CI meteorite simulants are destroyed within minutes when exposed to the level of solar irradiance encountered at heliocentric distances of up to about 0.2 au. Our results provide an explanation for the scarcity of dark, carbonaceous asteroids with perihelion distances less than 0.2 au, and for the observed mass-loss rate of the asteroid-like object 322P/SOHO 1 assuming its composition is similar to CI carbonaceous chondrites.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"448 ","pages":"Article 116942"},"PeriodicalIF":3.0,"publicationDate":"2026-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145973571","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 : 2026-01-06DOI: 10.1016/j.icarus.2026.116936
C. Pilorget , C. Ye , C.S. Edwards
Thermal IR spectroscopy has been widely used in the exploration of the Solar System to characterize the mineralogical composition of planetary surfaces. Beyond the identification of the different compounds, estimating their abundances presents significant challenges, hence the usual application of simplified models that generally assume linear mixtures for example. These approaches, relatively easy to use, might however lead to important biases. Here we present a novel model based on a Monte-Carlo approach to compute the radiative transfer within a granular medium where the grains are resolved. A critical aspect of our model is that it can more directly accept data acquired from lab experiments to simulate various types of mixtures (linear, intimate, layered) in a realistic manner. Variable thermal profiles can also be simulated in the sample. Such a model can be used to better constrain the abundances of mineral compounds in natural planetary surfaces. We present some first applications, in particular estimating potential biases when neglecting multiple scattering in the models. We also evaluate the effect of porosity and thermal gradients in a few limited cases to prove the feasibility for future applications.
{"title":"A Monte-Carlo radiative transfer model to simulate thermal infrared emission spectra from planetary surfaces: Mineralogical mixtures and thermal gradients","authors":"C. Pilorget , C. Ye , C.S. Edwards","doi":"10.1016/j.icarus.2026.116936","DOIUrl":"10.1016/j.icarus.2026.116936","url":null,"abstract":"<div><div>Thermal IR spectroscopy has been widely used in the exploration of the Solar System to characterize the mineralogical composition of planetary surfaces. Beyond the identification of the different compounds, estimating their abundances presents significant challenges, hence the usual application of simplified models that generally assume linear mixtures for example. These approaches, relatively easy to use, might however lead to important biases. Here we present a novel model based on a Monte-Carlo approach to compute the radiative transfer within a granular medium where the grains are resolved. A critical aspect of our model is that it can more directly accept data acquired from lab experiments to simulate various types of mixtures (linear, intimate, layered) in a realistic manner. Variable thermal profiles can also be simulated in the sample. Such a model can be used to better constrain the abundances of mineral compounds in natural planetary surfaces. We present some first applications, in particular estimating potential biases when neglecting multiple scattering in the models. We also evaluate the effect of porosity and thermal gradients in a few limited cases to prove the feasibility for future applications.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"448 ","pages":"Article 116936"},"PeriodicalIF":3.0,"publicationDate":"2026-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145922785","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 : 2025-12-29DOI: 10.1016/j.icarus.2025.116923
M. Escudero-Jiménez , M.A. López-Valverde , J. Peralta , T. Moya , A. Belmonte , A. Brines , I. Thomas , G. Villanueva , G. Liuzzi , E. Knutsen , S. Viscardy , F. González-Galindo , A. Modak , B. Funke , J.J. López-Moreno , J. Rodríguez , R. Sanz , F. Daerden , L. Trompet , A.S.J. Khayat , A.C. Vandaele
Here we update the search for two trace species of high interest in the Martian atmosphere, methane (CH) and carbonyl sulfide (OCS), using solar occultation (SO) measurements from the NOMAD spectrometer on board the Trace Gas Orbiter (TGO). Neither species has been detected in previous analyses of TGO’s dedicated SO instruments, ACS and NOMAD. Our approach focused on NOMAD-SO data, assessing in detail the calibration uncertainties to quantify systematic error components, and investigating if vertical averaging of spectra to reduce random noise would enhance the signal-to-noise ratio (SNR). The latter step required careful data cleaning with precise radiative transfer modeling and should improve upon earlier searches that analyzed spectra individually.
We examined 19,330 NOMAD SO spectra targeting CH and OCS, from diffraction orders 134 and 129, corresponding to 76 and 142 vertical scans, respectively. These scans span a wide range of latitudes and seasons over three Martian years (April 2018 to November 2022, MY34-MY36). No CH or OCS absorption features were detected and our composite vertical profiles (5–50 km tangent altitude) yielded stringent upper limits. For methane, the 1- upper limits typically lie around 0.5 ppbv, reaching 0.2 ppbv at some altitudes and locations. Our methane limits were primarily constrained by systematic uncertainties, particularly the residual baseline shape, and are therefore relatively higher than those previously reported in Knutsen et al. (2021), who processed the spectra differently to remove this effect. For OCS, our composite profiles indicate concentrations below 5 ppbv at low altitudes and below 2 ppbv in some cases, also at the 1- significance level.
Further improvements will require additional calibration refinements, ideally through better characterization of instrument behavior under thermal variations. As a practical step, narrowing the analyzed spectral intervals can reduce continuum uncertainties, provided contaminating features are absent. For methane features in diffraction order 134, such narrowing lowers uncertainties by a factor of three, getting closer to the most stringent limits previously reported (Knutsen et al., 2021).
在这里，我们更新了对火星大气中两种高度感兴趣的痕量物质的搜索，甲烷（CH4）和羰基硫化物（OCS），使用来自痕量气体轨道器（TGO）上的NOMAD光谱仪的太阳掩星（SO）测量。在TGO的专用SO仪器ACS和NOMAD之前的分析中都没有检测到这两种物种。我们的方法侧重于NOMAD-SO数据，详细评估校准不确定性以量化系统误差分量，并研究垂直平均光谱以减少随机噪声是否会提高信噪比（SNR）。后一步需要用精确的辐射传输建模仔细地清理数据，并且应该改进先前单独分析光谱的搜索。我们研究了19330个针对CH4和OCS的NOMAD SO光谱，分别对应于衍射阶134和129，分别对应于76和142垂直扫描。这些扫描跨越了三个火星年（2018年4月至2022年11月，MY34-MY36）的广泛纬度和季节。没有检测到CH4或OCS吸收特征，我们的复合垂直剖面（切线高度5-50 km）产生了严格的上限。对于甲烷，1-σ上限通常在0.5 ppbv左右，在某些高度和位置达到0.2 ppbv。我们的甲烷限值主要受到系统不确定性的限制，特别是剩余基线形状，因此相对高于Knutsen等人（2021）先前报道的数据，他们对光谱进行了不同的处理以消除这种影响。对于OCS，我们的复合剖面显示低海拔地区浓度低于5 ppbv，在某些情况下低于2 ppbv，也在1-σ显著水平上。进一步的改进将需要额外的校准改进，理想情况下，通过更好地表征仪器在热变化下的行为。作为一个实际步骤，在没有污染特征的情况下，缩小分析的光谱间隔可以减少连续体的不确定性。对于衍射阶为134的甲烷特征，这种缩小将不确定性降低了三倍，更接近先前报道的最严格限制（Knutsen et al., 2021）。
{"title":"Upper limits of CH4 and OCS in the Martian atmosphere from NOMAD/TGO solar occultation: A study of vertical averaging and systematic uncertainties","authors":"M. Escudero-Jiménez , M.A. López-Valverde , J. Peralta , T. Moya , A. Belmonte , A. Brines , I. Thomas , G. Villanueva , G. Liuzzi , E. Knutsen , S. Viscardy , F. González-Galindo , A. Modak , B. Funke , J.J. López-Moreno , J. Rodríguez , R. Sanz , F. Daerden , L. Trompet , A.S.J. Khayat , A.C. Vandaele","doi":"10.1016/j.icarus.2025.116923","DOIUrl":"10.1016/j.icarus.2025.116923","url":null,"abstract":"<div><div>Here we update the search for two trace species of high interest in the Martian atmosphere, methane (CH<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span>) and carbonyl sulfide (OCS), using solar occultation (SO) measurements from the NOMAD spectrometer on board the Trace Gas Orbiter (TGO). Neither species has been detected in previous analyses of TGO’s dedicated SO instruments, ACS and NOMAD. Our approach focused on NOMAD-SO data, assessing in detail the calibration uncertainties to quantify systematic error components, and investigating if vertical averaging of spectra to reduce random noise would enhance the signal-to-noise ratio (SNR). The latter step required careful data cleaning with precise radiative transfer modeling and should improve upon earlier searches that analyzed spectra individually.</div><div>We examined 19,330 NOMAD SO spectra targeting CH<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span> and OCS, from diffraction orders 134 and 129, corresponding to 76 and 142 vertical scans, respectively. These scans span a wide range of latitudes and seasons over three Martian years (April 2018 to November 2022, MY34-MY36). No CH<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span> or OCS absorption features were detected and our composite vertical profiles (5–50 km tangent altitude) yielded stringent upper limits. For methane, the 1-<span><math><mi>σ</mi></math></span> upper limits typically lie around 0.5 ppbv, reaching 0.2 ppbv at some altitudes and locations. Our methane limits were primarily constrained by systematic uncertainties, particularly the residual baseline shape, and are therefore relatively higher than those previously reported in Knutsen et al. (2021), who processed the spectra differently to remove this effect. For OCS, our composite profiles indicate concentrations below 5 ppbv at low altitudes and below 2 ppbv in some cases, also at the 1-<span><math><mi>σ</mi></math></span> significance level.</div><div>Further improvements will require additional calibration refinements, ideally through better characterization of instrument behavior under thermal variations. As a practical step, narrowing the analyzed spectral intervals can reduce continuum uncertainties, provided contaminating features are absent. For methane features in diffraction order 134, such narrowing lowers uncertainties by a factor of three, getting closer to the most stringent limits previously reported (Knutsen et al., 2021).</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"448 ","pages":"Article 116923"},"PeriodicalIF":3.0,"publicationDate":"2025-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145922783","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 : 2025-12-27DOI: 10.1016/j.icarus.2025.116926
Logan Dewsnap , Margaret Campbell-Brown
We examine the effects of assumptions in the calculation of electron line density of radar meteors on the value of luminous efficiency calculated using simultaneous radar and optical observations. We combine high-resolution optical measurements from the Canadian Automated Meteor Observatory (CAMO) with multi-frequency radar echoes from the Canadian Meteor Orbit Radar (CMOR). Previous work relating and has been limited to single-frequency radar observations, which requires additional modeling assumptions such as the initial trail radius (Weryk and Brown, 2013). In this work, we require model fits to all three frequencies at which CMOR operates, which provides better constraints which reduce the need for these assumptions, at the cost of significantly shrinking the pool of suitable data. Between 2017–2022, 299 candidates for three-frequency CMOR simultaneously observed by CAMO were identified, of which 1% were suitable for fitting. Although the fittable data set was too small to determine statistical trends, all events showed lower luminous efficiencies than those that would be found through single-frequency modeling. This emphasizes the need for better models of scattering from meteor trails in these studies.
{"title":"Meteor luminous efficiencies from simultaneous multi-frequency radar and high-resolution optical observations","authors":"Logan Dewsnap , Margaret Campbell-Brown","doi":"10.1016/j.icarus.2025.116926","DOIUrl":"10.1016/j.icarus.2025.116926","url":null,"abstract":"<div><div>We examine the effects of assumptions in the calculation of electron line density of radar meteors on the value of luminous efficiency calculated using simultaneous radar and optical observations. We combine high-resolution optical measurements from the Canadian Automated Meteor Observatory (CAMO) with multi-frequency radar echoes from the Canadian Meteor Orbit Radar (CMOR). Previous work relating <span><math><mi>β</mi></math></span> and <span><math><mi>τ</mi></math></span> has been limited to single-frequency radar observations, which requires additional modeling assumptions such as the initial trail radius (Weryk and Brown, 2013). In this work, we require model fits to all three frequencies at which CMOR operates, which provides better constraints which reduce the need for these assumptions, at the cost of significantly shrinking the pool of suitable data. Between 2017–2022, 299 candidates for three-frequency CMOR simultaneously observed by CAMO were identified, of which 1% were suitable for fitting. Although the fittable data set was too small to determine statistical trends, all events showed lower luminous efficiencies than those that would be found through single-frequency modeling. This emphasizes the need for better models of scattering from meteor trails in these studies.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"448 ","pages":"Article 116926"},"PeriodicalIF":3.0,"publicationDate":"2025-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145922784","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 : 2025-12-26DOI: 10.1016/j.icarus.2025.116924
G.O. Barbosa , T. Santana , O.C. Winter
We investigate the long-term dynamical stability of moons orbiting planets by performing high-resolution -body simulations across five planet-to-star mass ratios ( to ). Moons are modeled as massless test particles and their orbits are initialized at pericenter, where stellar perturbations are minimized. This setup yields upper-envelope estimates of the outermost stable semimajor axis () under optimally phased initial conditions, which we systematically map as a function of eccentricity. We derive empirical fits for in each regime and observe that the stable region contracts with increasing eccentricity and decreasing planetary mass. For larger values of , we identify a detached island of stability at intermediate eccentricities (), which we show to be associated with the evection resonance; additional integrations confirm libration of the resonant angle. We examine the sensitivity of to the initial satellite–star mean-anomaly offset () and find that orbital phase can modulate the critical stability threshold by . Our updated stability criteria therefore consist of: (i) new empirical fits for the critical semimajor axis as a function of eccentricity, (ii) its systematic dependence on the planet-to-star mass ratio, and (iii) the role of the evection resonance and orbital phase in extending stability beyond classical limits. These results provide a refined framework for assessing exomoon survivability across diverse planetary systems. The empirical relations presented in this work can be directly employed to constrain the parameter space in observational searches for exomoons.
{"title":"On the stability limits for moons orbiting planets: A numerical investigation","authors":"G.O. Barbosa , T. Santana , O.C. Winter","doi":"10.1016/j.icarus.2025.116924","DOIUrl":"10.1016/j.icarus.2025.116924","url":null,"abstract":"<div><div>We investigate the long-term dynamical stability of moons orbiting planets by performing high-resolution <span><math><mi>N</mi></math></span>-body simulations across five planet-to-star mass ratios (<span><math><mrow><mi>μ</mi><mo>=</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math></span> to <span><math><mrow><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup></mrow></math></span>). Moons are modeled as massless test particles and their orbits are initialized at pericenter, where stellar perturbations are minimized. This setup yields upper-envelope estimates of the outermost stable semimajor axis (<span><math><msub><mrow><mi>a</mi></mrow><mrow><mi>E</mi></mrow></msub></math></span>) under optimally phased initial conditions, which we systematically map as a function of eccentricity. We derive empirical fits for <span><math><mrow><msub><mrow><mi>a</mi></mrow><mrow><mi>E</mi></mrow></msub><mrow><mo>(</mo><mi>e</mi><mo>)</mo></mrow></mrow></math></span> in each <span><math><mi>μ</mi></math></span> regime and observe that the stable region contracts with increasing eccentricity and decreasing planetary mass. For larger values of <span><math><mi>μ</mi></math></span>, we identify a detached island of stability at intermediate eccentricities (<span><math><mrow><mn>0</mn><mo>.</mo><mn>2</mn><mo>≲</mo><mi>e</mi><mo>≲</mo><mn>0</mn><mo>.</mo><mn>7</mn></mrow></math></span>), which we show to be associated with the evection resonance; additional integrations confirm libration of the resonant angle. We examine the sensitivity of <span><math><msub><mrow><mi>a</mi></mrow><mrow><mi>E</mi></mrow></msub></math></span> to the initial satellite–star mean-anomaly offset (<span><math><mrow><mi>Δ</mi><mi>M</mi></mrow></math></span>) and find that orbital phase can modulate the critical stability threshold by <span><math><mrow><mo>≲</mo><mn>10</mn><mtext>%</mtext></mrow></math></span>. Our updated stability criteria therefore consist of: (i) new empirical fits for the critical semimajor axis as a function of eccentricity, (ii) its systematic dependence on the planet-to-star mass ratio, and (iii) the role of the evection resonance and orbital phase in extending stability beyond classical limits. These results provide a refined framework for assessing exomoon survivability across diverse planetary systems. The empirical relations presented in this work can be directly employed to constrain the parameter space in observational searches for exomoons.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"448 ","pages":"Article 116924"},"PeriodicalIF":3.0,"publicationDate":"2025-12-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145882261","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 : 2025-12-24DOI: 10.1016/j.icarus.2025.116919
J.C. Gérard , L. Soret , B. Hubert , R. Lillis , S. Jain , J. Deighan
Neutral carbon emissions have been observed in Far Ultraviolet spectra (FUV) of the Martian aurora with the Emirates Mars Ultraviolet Spectrometer (EMUS) instrument on board the Emirates Mars Mission (EMM). Oxygen emissions at 130.4 and 135.6 nm have been used to map the auroral morphology and its dependence on solar wind parameters. The CI emissions at 156.1 and 165.7 nm are excited by collisions between energetic electrons and CO2, CO and C. We present Monte Carlo simulations of the altitude distributions of both features showing that electron collisions with ambient CO2 molecules are the dominant source, followed by collisions on CO, while direct impact on C atoms is several orders of magnitude smaller. Since the C atom fragments resulting from dissociation are produced with a speed exceeding by far the thermal velocity, the optical depth is negligible. Consequently, the 156.1 and 165.7 nm photons are not self-absorbed, and the calculation of the emission rates does not require consideration of radiative transfer, unlike the OI 130.4 nm triplet. We present calculations of the efficiency of the carbon emissions for a range of incident auroral electrons energies. We illustrate the energy dependence of the intensity ratios between the oxygen 130.4 and 135.6 nm and the carbon 165.7 nm emissions. These ratios may be used to remotely characterize the spatial distribution of the incident electron energies in spectral FUV maps of the aurora.
{"title":"Far ultraviolet carbon emissions in the Mars aurora: Brightness, intensity ratios and seasonal dependence","authors":"J.C. Gérard , L. Soret , B. Hubert , R. Lillis , S. Jain , J. Deighan","doi":"10.1016/j.icarus.2025.116919","DOIUrl":"10.1016/j.icarus.2025.116919","url":null,"abstract":"<div><div>Neutral carbon emissions have been observed in Far Ultraviolet spectra (FUV) of the Martian aurora with the Emirates Mars Ultraviolet Spectrometer (EMUS) instrument on board the Emirates Mars Mission (EMM). Oxygen emissions at 130.4 and 135.6 nm have been used to map the auroral morphology and its dependence on solar wind parameters. The CI emissions at 156.1 and 165.7 nm are excited by collisions between energetic electrons and CO<sub>2</sub>, CO and C. We present Monte Carlo simulations of the altitude distributions of both features showing that electron collisions with ambient CO<sub>2</sub> molecules are the dominant source, followed by collisions on CO, while direct impact on C atoms is several orders of magnitude smaller. Since the C atom fragments resulting from dissociation are produced with a speed exceeding by far the thermal velocity, the optical depth is negligible. Consequently, the 156.1 and 165.7 nm photons are not self-absorbed, and the calculation of the emission rates does not require consideration of radiative transfer, unlike the OI 130.4 nm triplet. We present calculations of the efficiency of the carbon emissions for a range of incident auroral electrons energies. We illustrate the energy dependence of the intensity ratios between the oxygen 130.4 and 135.6 nm and the carbon 165.7 nm emissions. These ratios may be used to remotely characterize the spatial distribution of the incident electron energies in spectral FUV maps of the aurora.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"448 ","pages":"Article 116919"},"PeriodicalIF":3.0,"publicationDate":"2025-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145882258","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 : 2025-12-22DOI: 10.1016/j.icarus.2025.116922
Christopher O. Johnston , Alireza Mazaheri , Eric C. Stern
A perspective on the luminous efficiency approach for determining the pre-atmospheric mass of a meteoroid from a measured light-curve is presented for meteors in the continuum flow regime. This perspective interprets the mass-loss rate evaluated from the luminous efficiency approach as a solution to the meteoroid surface energy balance, with the measured light-curve serving as a proxy for the radiative heating to the meteoroid surface. This differs from the standard interpretation that equates the radiation from the light-curve to a change in the kinetic energy of the meteor. Mathematically, the developed perspective is identical to the standard luminous efficiency approach, except that the deceleration term is shown to be extraneous. This perspective provides a clear relationship between the measured light-curve and the mass loss of a meteor, which is based on the observation that the radiative heating that drives the mass loss (through the surface energy balance) also provides the radiation for the light-curve. Furthermore, this perspective provides a simple mathematical framework for interpreting the impact of fragmentation on the luminous efficiency. This framework shows that the luminous efficiency of a fragmented meteoroid is a weighted sum of the luminous efficiency from the various fragments, which may each be assessed based on single-body simulations. To generate these single-body simulations, state-of-the-art flowfield and radiation simulations are performed for meteoroid diameters ranging from 0.02 to 100 m, velocities ranging from 12 to 24 km/s, and altitudes ranging from 20 to 50 km. The luminous efficiency values resulting from these simulations are distilled into a correlation and applied to trajectories resulting from the fragment cloud method. This allows the integral luminous efficiency to be computed using the developed luminous efficiency model and defined fragmentation framework. Both the silicon and visible passbands are considered. For the silicon passband, the computed integral luminous efficiency values track closely with the experimentally derived integral luminous efficiency model developed by Brown et al. (2002). This represents the first theoretical derivation of the integral luminous efficiency approach based on fully coupled radiation and ablation simulations with viscous effects, which also captures the impact of individual meteoroids that are combined using the developed fragmentation framework.
{"title":"A perspective on the luminous efficiency approach for meteoroid mass estimation","authors":"Christopher O. Johnston , Alireza Mazaheri , Eric C. Stern","doi":"10.1016/j.icarus.2025.116922","DOIUrl":"10.1016/j.icarus.2025.116922","url":null,"abstract":"<div><div>A perspective on the luminous efficiency approach for determining the pre-atmospheric mass of a meteoroid from a measured light-curve is presented for meteors in the continuum flow regime. This perspective interprets the mass-loss rate evaluated from the luminous efficiency approach as a solution to the meteoroid surface energy balance, with the measured light-curve serving as a proxy for the radiative heating to the meteoroid surface. This differs from the standard interpretation that equates the radiation from the light-curve to a change in the kinetic energy of the meteor. Mathematically, the developed perspective is identical to the standard luminous efficiency approach, except that the deceleration term is shown to be extraneous. This perspective provides a clear relationship between the measured light-curve and the mass loss of a meteor, which is based on the observation that the radiative heating that drives the mass loss (through the surface energy balance) also provides the radiation for the light-curve. Furthermore, this perspective provides a simple mathematical framework for interpreting the impact of fragmentation on the luminous efficiency. This framework shows that the luminous efficiency of a fragmented meteoroid is a weighted sum of the luminous efficiency from the various fragments, which may each be assessed based on single-body simulations. To generate these single-body simulations, state-of-the-art flowfield and radiation simulations are performed for meteoroid diameters ranging from 0.02 to 100 m, velocities ranging from 12 to 24 km/s, and altitudes ranging from 20 to 50 km. The luminous efficiency values resulting from these simulations are distilled into a correlation and applied to trajectories resulting from the fragment cloud method. This allows the integral luminous efficiency to be computed using the developed luminous efficiency model and defined fragmentation framework. Both the silicon and visible passbands are considered. For the silicon passband, the computed integral luminous efficiency values track closely with the experimentally derived integral luminous efficiency model developed by Brown et al. (2002). This represents the first theoretical derivation of the integral luminous efficiency approach based on fully coupled radiation and ablation simulations with viscous effects, which also captures the impact of individual meteoroids that are combined using the developed fragmentation framework.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"447 ","pages":"Article 116922"},"PeriodicalIF":3.0,"publicationDate":"2025-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837294","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 : 2025-12-22DOI: 10.1016/j.icarus.2025.116920
Satyandra M. Sharma , Varun Sheel , Martin Pätzold
Venus, in the absence of an intrinsic magnetic field, undergoes a direct interaction between its ionosphere and the solar wind. Previous missions, including Mariner, Venera, and the Pioneer Venus Orbiter (PVO), reported a recurring localized increase in electron density, often termed a ”bulge,” at altitudes between 160 and 200 km. This study investigates this topside bulge using over 200 dayside electron density profiles derived from the Venus Radio Science experiment (VeRa) onboard the Venus Express (VEX). We employ an automated, gradient-based classification algorithm to provide a quantitative and reproducible method for identifying and categorizing the bulge morphology into three types. Type 1 profiles exhibit a distinct secondary peak above the main V2 layer. Type 2 profiles display a shoulder-like feature near the bulge altitude. Type 3 bulges are not visually apparent but can be identified through residuals obtained after subtracting a Chapman layer fit to the V2 peak. The bulge is detected in over 80% of the analyzed profiles, with a higher occurrence during periods of low solar activity and at lower solar zenith angles (). Type 1 morphologies are only observed at low latitudes (within 40°N). The peak altitude of the bulge negatively correlates with , suggesting that thermospheric cooling toward the terminator significantly influences the bulge altitude. The occurrence patterns and morphological characteristics indicate that the bulge is likely influenced by external drivers, such as solar wind interaction, rather than being solely a result of local photochemical processes.
{"title":"Identification and characterization of the topside bulge of the Venusian ionosphere","authors":"Satyandra M. Sharma , Varun Sheel , Martin Pätzold","doi":"10.1016/j.icarus.2025.116920","DOIUrl":"10.1016/j.icarus.2025.116920","url":null,"abstract":"<div><div>Venus, in the absence of an intrinsic magnetic field, undergoes a direct interaction between its ionosphere and the solar wind. Previous missions, including <em>Mariner</em>, <em>Venera</em>, and the <em>Pioneer Venus Orbiter</em> (<em>PVO</em>), reported a recurring localized increase in electron density, often termed a ”bulge,” at altitudes between 160 and 200 km. This study investigates this topside bulge using over 200 dayside electron density profiles derived from the <em>Venus Radio Science experiment (VeRa)</em> onboard the <em>Venus Express (VEX)</em>. We employ an automated, gradient-based classification algorithm to provide a quantitative and reproducible method for identifying and categorizing the bulge morphology into three types. Type 1 profiles exhibit a distinct secondary peak above the main V2 layer. Type 2 profiles display a shoulder-like feature near the bulge altitude. Type 3 bulges are not visually apparent but can be identified through residuals obtained after subtracting a Chapman layer fit to the V2 peak. The bulge is detected in over 80% of the analyzed profiles, with a higher occurrence during periods of low solar activity and at lower solar zenith angles (<span><math><mrow><mi>S</mi><mi>Z</mi><mi>A</mi><mi>s</mi></mrow></math></span>). Type 1 morphologies are only observed at low latitudes (within <span><math><mo>±</mo></math></span>40°N). The peak altitude of the bulge negatively correlates with <span><math><mrow><mi>S</mi><mi>Z</mi><mi>A</mi></mrow></math></span>, suggesting that thermospheric cooling toward the terminator significantly influences the bulge altitude. The occurrence patterns and morphological characteristics indicate that the bulge is likely influenced by external drivers, such as solar wind interaction, rather than being solely a result of local photochemical processes.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"448 ","pages":"Article 116920"},"PeriodicalIF":3.0,"publicationDate":"2025-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145839436","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 : 2025-12-20DOI: 10.1016/j.icarus.2025.116921
Tianyi Xu , Wei Cai , Yunzhao Wu , Xiaoping Zhang , Yanyan Xu , Meizhu Wang , Zhiping He , Cunhui Li , Weidong Qiao , Jinyou Tao , Jianfeng Yang
The Chang'E-6 mission landing on the far side of the Moon, conducted in-situ measurements of the lunar regolith using a Panoramic Camera and Lunar Mineralogical Spectrometer. The rocket exhaust created distinct bright zones around the landing site, categorized as focused blast zones and diffuse blast zones. This study analyzes the photometric properties across native regolith, blast zones, and underfoot regions using the Hapke model, integrating data from both the panoramic camera and the spectrometer. Results show that backscattering increases with proximity to the lander. The observed brightening within the blast zone is primarily attributed to the removal of fine particles and the exposure of immature regolith. Regions immediately adjacent to the lander exhibit lower albedo, forward scattering behavior, higher spectral slopes, and a shallower 1 μm absorption band, suggesting the presence of glassy materials and an increased abundance of agglutinates.
{"title":"Lunar surface modification revealed by in-situ photometric observations from Chang'E-6","authors":"Tianyi Xu , Wei Cai , Yunzhao Wu , Xiaoping Zhang , Yanyan Xu , Meizhu Wang , Zhiping He , Cunhui Li , Weidong Qiao , Jinyou Tao , Jianfeng Yang","doi":"10.1016/j.icarus.2025.116921","DOIUrl":"10.1016/j.icarus.2025.116921","url":null,"abstract":"<div><div>The Chang'E-6 mission landing on the far side of the Moon, conducted in-situ measurements of the lunar regolith using a Panoramic Camera and Lunar Mineralogical Spectrometer. The rocket exhaust created distinct bright zones around the landing site, categorized as focused blast zones and diffuse blast zones. This study analyzes the photometric properties across native regolith, blast zones, and underfoot regions using the Hapke model, integrating data from both the panoramic camera and the spectrometer. Results show that backscattering increases with proximity to the lander. The observed brightening within the blast zone is primarily attributed to the removal of fine particles and the exposure of immature regolith. Regions immediately adjacent to the lander exhibit lower albedo, forward scattering behavior, higher spectral slopes, and a shallower 1 μm absorption band, suggesting the presence of glassy materials and an increased abundance of agglutinates.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"447 ","pages":"Article 116921"},"PeriodicalIF":3.0,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837295","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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