Icarus最新文献

{"title":"Laboratory measurements of the expansion characteristics of dust impact plasmas","authors":"L. Nouzák ,&nbsp;K. Edwards ,&nbsp;J. Fontanese ,&nbsp;T. Munsat ,&nbsp;J. Pavlů ,&nbsp;Z. Sternovsky","doi":"10.1016/j.icarus.2025.116586","DOIUrl":"10.1016/j.icarus.2025.116586","url":null,"abstract":"<div><div>The impact ionization process provides a method for the sensitive detection and analysis of dust particles in space. Dust particles impacting solid surfaces at high velocity evaporate and partially ionize. The characterization of the generated transient impact plasma plume is important for the understanding of dust impact signals detected in space by antenna instruments, or for the optimization of dust instrumentation. The angular and velocity distributions of the ions emerging from the dust impact plasma are measured experimentally using a Delay-Line Detector (DLD) setup. A small tungsten target is exposed to the impacts of micron- and submicron-sized iron dust particles using the dust accelerator facility operated at the University of Colorado. The ions from the impact plasma expand in a field-free region and are detected by the DLD. The angular and velocity distributions are calculated from the spatial and temporal distributions of the recorded ions. The velocity distribution measurements are performed for dust impact velocity ranges of <span><math><mn>2</mn><mo>−</mo><mn>5</mn></math></span>, <span><math><mn>10</mn><mo>−</mo><mn>15</mn></math></span>, and &gt;<span><math><mn>20</mn><mspace></mspace><mi>km</mi><mo>/</mo><mi>s</mi></math></span>. The ion velocity distribution is relatively narrow (≤ 10 km/s) for the lowest dust velocity range, but significantly wider (exceeding 50 km/s) for the higher dust impact speeds. The velocity distribution can be decomposed into contributions from the most prevalent ion species in the impact plasma (Fe⁺, Na⁺, C⁺, and H⁺). The measurements suggest that for dust impact speeds greater than 10 km/s the translational energy of the ions is in the range of about 3–8 eV, while the superimposed thermal energy is about 1 eV, with only a weak variation with impact speed and ion species. The ion angular distribution was measured by averaging the signals from 110 dust impacts from a 10–15 km/s dust impact speed and is consistent with a cosine distribution.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"435 ","pages":"Article 116586"},"PeriodicalIF":2.5,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143767475","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":"Love numbers for Io with a magma ocean","authors":"Burak Aygün,&nbsp;Ondřej Čadek","doi":"10.1016/j.icarus.2025.116567","DOIUrl":"10.1016/j.icarus.2025.116567","url":null,"abstract":"<div><div>The volcanic activity of Jupiter’s moon Io is driven by the heat generated by tidal deformation induced by its orbital resonance with Europa and Ganymede. The question of whether tidal dissipation primarily occurs in a partially molten solid layer (“magmatic sponge”) or in a hypothetical liquid magma ocean has long been a subject of debate. The data collected by the Juno spacecraft during two recent flybys of Io has allowed, for the first time, to quantify Io’s tidal deformation. The analysis of the data by Park et al. (2024) reveals that the Love number <span><math><msub><mrow><mi>k</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> is about 0.125 and the tidal dissipation parameter <span><math><mi>Q</mi></math></span> is about 11.4. These values are compatible with a solid mantle but they do not exclude the possibility that a global magma ocean exists in the deep (<span><math><mo>&gt;</mo></math></span>320 km) interior. Using a model based on the solution of the Navier–Stokes equation, we investigate the dependence of the Love number on the position of the ocean and examine how much it is affected by the Coriolis force, an effect that was not included in the study of Park et al. (2024). Varying the viscosity of the magma, the depth and the thickness of the ocean in the range of <span><math><mrow><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>2</mn></mrow></msup></mrow></math></span>–<span><math><mrow><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>7</mn></mrow></msup></mrow></math></span> Pa<!--> <!-->s, 50–400 km and 0.1–20 km, respectively, and considering only the models with a dissipation power of about 100 TW, we show that a magma ocean located at a depth of <span><math><mrow><mo>≲</mo><mn>200</mn></mrow></math></span> km predicts either too large <span><math><msub><mrow><mi>k</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> or too long time lag, implying that the existence of a shallow magma ocean in Io is unlikely. A thin (<span><math><mo>&lt;</mo></math></span>10 km) magma ocean located at a depth of <span><math><mrow><mo>≳</mo><mn>250</mn></mrow></math></span> km is compatible with the observation and could, in principle, be detected by accurate measurement of degree 2 zonal and sectorial Love numbers. Our results are in general agreement with those of Park et al. (2024), indicating that Io’s enormous volcanic activity is unlikely to be driven by a global fluid magma ocean located at a shallow depth. This conclusion is conditioned by the reliability of the method used to interpret the Juno data. As the tidal response of Io with a magma ocean is affected by the Coriolis force, the Love number depends on the harmonic order, which can complicate the analysis of the information collected during the flybys. The effect of fluid tides was not considered in the data processing, and therefore, the conclusions of Park et al. (2024) cannot be definitely confirmed.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"436 ","pages":"Article 116567"},"PeriodicalIF":2.5,"publicationDate":"2025-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143783674","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":"Laboratory experiments on the visible to near- infrared (VNIR) spectroscopy of water ice and lunar highland simulant mixtures: Effects of particle size, particle shape, phase angle, and ice abundance","authors":"N. de Castro,&nbsp;S. Li","doi":"10.1016/j.icarus.2025.116578","DOIUrl":"10.1016/j.icarus.2025.116578","url":null,"abstract":"<div><div>Surficial water ice has been detected in the permanently shaded regions (PSRs) near the lunar poles. Water ice can be detected by its diagnostic absorption features of ice at 1.0, 1.25, 1.5, and 2.0 μm, as well as high reflectance in the VIS region. However, the effects of particle size and shape, ice abundance, and phase angle on the VNIR spectra of ice mixtures remain poorly understood, posing a challenge for detections of water ice on the lunar surface. In this study, we measured the VNIR spectra of pure water ice and mixtures of water ice and a lunar highland regolith simulant (HRS). We investigated the effects of particle size of ice (0–250 μm), particle shape of ice (angular vs. spherical), phase angle (0–105°), and ice abundance (0–50 wt%) on the VNIR spectra of water ice and HRS mixtures from 350 to 2500 nm. Our results show that coarser ice particles exhibit stronger NIR absorptions and lower VIS reflectance, attributable to increased photon absorptions due to longer optical pathlengths. Similarly, the longer optical pathlengths of spherical particles relative to angular ones result in lower VIS reflectance. The forward scattering nature of water ice leads to increased VIS reflectance at high phase angles (&gt;90°), suggesting that high phase angles are optimal for lunar water ice detection. Phase angles have a negligible effect on the strength of the NIR absorptions of ice, especially when ice is present at low ice abundances (&lt;20 wt%) in intimate mixtures with the HRS. Lastly, our findings suggest that the NIR absorptions near 1.25, 1.5, and 2.0 μm rapidly deepen at very low ice concentrations (0–5 wt%). We also find a linear relationship between VIS reflectance and ice content in intimate mixtures with a HRS containing 0–50 wt% ice. The findings of this study offer a detailed framework for detecting and analyzing water ice on the lunar surface via VNIR spectroscopy.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"435 ","pages":"Article 116578"},"PeriodicalIF":2.5,"publicationDate":"2025-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143759235","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":"Dimension-ratio-based observability analysis of asteroid photometric model and optimization strategy for completely observable satellite detection","authors":"Yangyang Li ,&nbsp;Jin Liu ,&nbsp;Xiaolin Ning ,&nbsp;Xin Ma","doi":"10.1016/j.icarus.2025.116583","DOIUrl":"10.1016/j.icarus.2025.116583","url":null,"abstract":"<div><div>The physical parameters of asteroids are obtained through the inversion of the asteroid photometric model. However, due to limitations in observation orientation, asteroid lightcurves exhibit insensitivity to certain errors in physical parameters. This insensitivity leads to multiple virtual solutions when inverting the asteroid photometric model. To theoretically evaluate the performance of this inversion, we propose a dimension-ratio-based observability analysis of the asteroid photometric model. Firstly, we employ the traditional observability analysis method to generate candidate vectors representing errors in physical parameters. Subsequently, we select unobservable vectors corresponding to very small chi-square values from these candidate vectors. The unobservable vectors span into an unobservable subspace, meaning that large errors within this unobservable subspace result in minimal disturbances in lightcurves, indicating low estimation accuracy for this unobservable subspace. Finally, the dimension-ratio, which is the ratio of the dimension of unobservable subspace to the total number of physical parameters, is used for the observability degree. Building upon this, in response to the issue that ground-based detection hardly acquires completely observable physical parameters, we propose an optimization strategy for completely observable satellite detection, utilizing the hippopotamus optimization algorithm to optimize the satellite orbit. In this optimized orbit, the physical parameters of the asteroid become completely observable. Simulation results demonstrate that the distribution of virtual solutions is consistent with our theoretical analysis. Furthermore, a unique solution available for estimating the physical parameters of the asteroid exists in the optimized satellite orbit.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"436 ","pages":"Article 116583"},"PeriodicalIF":2.5,"publicationDate":"2025-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143786108","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":"Viewing lobate patterns on Mars and Earth as climate modulated fluid-like instabilities","authors":"JohnPaul Sleiman ,&nbsp;Susan J. Conway ,&nbsp;Andreas Johnsson ,&nbsp;James Wray ,&nbsp;Rachel Glade","doi":"10.1016/j.icarus.2025.116580","DOIUrl":"10.1016/j.icarus.2025.116580","url":null,"abstract":"<div><div>Lobate features found on high-latitude slopes on Mars resemble terrestrial cold-climate soil patterns known as solifluction lobes. Whether this provides evidence of freeze thaw processes on Mars or pattern equifinality is up for debate. Guided by recently developed theory for solifluction pattern formation inspired by fluid instabilities, here we compare HiRISE imagery of Martian lobes with a large dataset of solifluction lobes on Earth and find that they exhibit similar morphologic scaling. Our data show that Martian lobes are roughly 2.6 times taller than their Earth counterparts, indicative of lobe height set by cohesive soil strength under different gravitational conditions. We also explore possible climate controls on Martian lobe morphology using elevation, aspect, and temperature data. Our work suggests mechanistic similarities between lobate patterns on Earth and Mars that point toward icy origins for these features, with implications for our understanding of climate controls on Martian surface processes.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"435 ","pages":"Article 116580"},"PeriodicalIF":2.5,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143739123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Understanding compositional evolution of hollows at Dominici crater, Mercury","authors":"A. Emran,&nbsp;K.M. Stack","doi":"10.1016/j.icarus.2025.116576","DOIUrl":"10.1016/j.icarus.2025.116576","url":null,"abstract":"<div><div>Hollows on Mercury are small depressions formed by volatile loss, providing important clues about the volatile inventory of the planet's surface and shallow subsurface. We investigate the composition of hollows in various phases of devolatilization at Dominici crater. By applying a machine learning approach to MESSENGER Mercury Dual Imaging System data, we defined surface units within the study area and extracted their reflectance spectra. We applied linear (areal) spectral modeling using laboratory sulfides, chlorides, graphite, and silicate mineral spectra to estimate the composition of hollows and their surrounding terrains. At Dominici, the hollow on the crater rim/wall is interpreted to be active, while that in the center of the crater is interpreted as a waning hollow. We find that the active hollow predominantly comprises silicates (augite and albite), with a trace amount of graphite and CaS. In contrast, waning hollows contain marginally elevated sulfides (MgS and CaS) and graphite, but slightly lower silicates than the active hollow. The spectra of low reflectance terrain surrounding the hollows appear to be dominated by graphite and sulfides, which contribute to its darker appearance. We suggest that hollow at the crater forms due to thermal decomposition of sulfides, primarily MgS possibly mixed with CaS, as well as possible the depletion of graphite. As devolatilization wanes, a mixture of predominantly silicate minerals remains in the hollows — impeding further vertical growth.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"435 ","pages":"Article 116576"},"PeriodicalIF":2.5,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143739124","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":"Outgassing of ice agglomerates II","authors":"Konrad J. Kossacki","doi":"10.1016/j.icarus.2025.116541","DOIUrl":"10.1016/j.icarus.2025.116541","url":null,"abstract":"<div><div>The aim of the work is to analyze limitations of the applicability of equations for the rate of outgassing of the nuclei of comets. I presented the results of experiments performed using large samples composed of agglomerates of radii up to few centimeters. In this respect the present work is the continuation of the paper Kossacki et al. (2023) about the outgassing of mixtures of millimeter sized agglomerates. The ratio between the radii of agglomerates and the radii of smallest grains present in agglomerates was previously about 10 and now is about 100. The measured changes of masses of the samples during experiments were compared with the results of calculations based on the structures of the samples and the recorded temperatures. Considered were two different mathematical models. One requires knowledge of the porosity, but not of the granulation of material (Kossacki 2021), while the second assumes knowledge of the radii of the smallest grains and of the agglomerates, as well as of the vapor pressure in pores between agglomerates (Kossacki et al. 2023). It was found that: (1) both models can reproduce the results of experiments and (2) the gas pressure in pores normalized to the pressure of phase equilibrium exhibits strong dependence on the temperature and weak dependence on the sizes of agglomerates. Based on the presented results I recommend to use equations which do not include the vapor pressure in pores.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"435 ","pages":"Article 116541"},"PeriodicalIF":2.5,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143734992","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":"Hypervelocity impact experiments in iron alloy targets","authors":"Yangyu Lu ,&nbsp;Meng-Hua Zhu ,&nbsp;Qiang Wu ,&nbsp;Siyuan Ren","doi":"10.1016/j.icarus.2025.116575","DOIUrl":"10.1016/j.icarus.2025.116575","url":null,"abstract":"<div><div>In this work, we conducted hypervelocity impact experiments on iron alloy targets (FeNi36 and stainless steel SS304) at various impact angles using a two-stage light-gas gun. Our investigation focuses on the structure of impact craters formed on metallic targets, with implications for understanding potential crater formation on metal asteroids, such as those on Psyche. Our results show distinct differences in the crater morphologies of FeNi36 and SS304 targets, particularly in terms of crater size and rim features, which can be attributed to variations in material properties such as hardness and strength. We derived empirical equations from both our current experiments and previous studies with a wide range of iron alloy targets to estimate crater diameter and depth. The experimental results from our oblique impacts on iron alloy targets demonstrate that the variation in crater dimensions (i.e., depth, length, and diameter) primarily follow a <em>sinθ</em> relationship with respect to the impact angle. For metallic targets at oblique impacts, the material properties of both the projectile and target exert a significant influence on crater morphology, particularly at low impact angles, where they notably affect crater length. These findings may provide additional understanding of crater formation process on metal asteroids, such as those on the Psyche asteroid.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"435 ","pages":"Article 116575"},"PeriodicalIF":2.5,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143748327","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":"The role of pre-existing topography in modulating lunar lava flow widths, depths and channel structure","authors":"Yuan Chen ,&nbsp;James W. Head ,&nbsp;Lionel Wilson ,&nbsp;Mikhail A. Kreslavsky ,&nbsp;Edward Davis ,&nbsp;Xingguo Zeng ,&nbsp;Xin Ren ,&nbsp;Jianjun Liu ,&nbsp;Chunlai Li","doi":"10.1016/j.icarus.2025.116564","DOIUrl":"10.1016/j.icarus.2025.116564","url":null,"abstract":"<div><div>Lunar volcanism is one of the most important endogenic processes on the Moon. The final morphology of a lava flow depends on (a) the composition of the magma, which determines its rheology, (b) the effusion rate, controlled by the geometry of the dike transferring the magma to the surface and the overpressure in the magma source, (c) the lava cooling behavior influenced by whether the flow is laminar or turbulent, (d) the total volume of magma erupted, and the topography of the surface onto which the lava flows. Thus, studying the morphology of flows sheds light on their eruption conditions, and has implications for the nature of the magma source region. In this study, we document the effects of topography on a well-preserved Eratosthenian-aged lava flow that most likely originated from the volcanic complex around Euler Crater in Mare Imbrium. We assess how the observations can improve our understanding of previous models of lunar lava flow emplacement and cooling behavior. We find that: 1) the pre-existing topography significantly affected the morphology of the flow; 2) several low wrinkle ridges predating the eruption and controlling the flow path underwent significant tectonic modification after lava emplacement; 3) variations in the extent of lava channel/levee structures along the flow are linked to turbulent/laminar flow modes; 4) the emplacement of the lava flow investigated here was probably completed in about a week, occurring in the very early period of regional wrinkle ridge formation. This lava flow history provides new insight into the interplay of regional volcanism and tectonism in Mare Imbrium and late-stage lunar thermal evolution in general.</div></div><div><h3>Key points</h3><div><ul><li><span>•</span><span><div>The geometric and morphological features of lava flows can be significantly affected by pre-existing topography.</div></span></li><li><span>•</span><span><div>The observed channel within a well-preserved Imbrium lava flow is interpreted to imply a transformation of flow mode from turbulent to laminar.</div></span></li><li><span>•</span><span><div>We deduced the paleo-geological sequence of processes forming this Imbrium lava flow.</div></span></li></ul></div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"435 ","pages":"Article 116564"},"PeriodicalIF":2.5,"publicationDate":"2025-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143734993","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Surface activity of H2O and CO2 on comet 103P/Hartley2 derived from EPOXI/HRI images","authors":"Yinsi Shou ,&nbsp;Michael Combi ,&nbsp;Lori Feaga ,&nbsp;Valeriy Tenishev ,&nbsp;Tony Farnham ,&nbsp;Nicolas Fougere","doi":"10.1016/j.icarus.2025.116557","DOIUrl":"10.1016/j.icarus.2025.116557","url":null,"abstract":"<div><div>On November 4, 2010, the EPOXI extended the mission of the Deep Impact spacecraft, flew by comet 103P/Hartley 2, and made a series of spectral images in both the infrared and the visible. The High-Resolution Instrument Infrared Spectrometer (HRI-IR) observed the comet and its surrounding coma, enabling maps in the light of the infrared emissions of H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O at <span><math><mrow><mn>2</mn><mo>.</mo><mn>7</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span> and CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> at <span><math><mrow><mn>4</mn><mo>.</mo><mn>3</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span> to be made. We have extended an inversion method originally developed to map out potential activity on the surface of comet 67P/Churyumov–Gerasimenko from ROSINA mass spectrometer measurements as part of the Rosetta mission to enable making similar nucleus surface activity maps from 2-D images of H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O and CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> in the inner coma of Hartley 2. Processed close-up column density images show the existence of extended sources for H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O and CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>. Column density profiles specific to an icy grain extended source are derived based on a simple Monte Carlo grain model, and are used to remove the effects of an extended source from a set of 11 spectral maps of each species taken within 1 h of closest approach. We apply the inversion technique to the processed HRI-IR spectral images to calculate the distribution of potential surface activity of both species over the whole surface. Comparisons are made between the processed images, fitted images from the inversion model, and synthetic images generated by the Direct Simulation Monte Carlo (DSMC) coma model, demonstrating that the derived surface activity distributions can reproduce most patterns in the observed images. Production rates from direct nucleus sublimation during the closet approach period are characterized based on the DSMC model results.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"435 ","pages":"Article 116557"},"PeriodicalIF":2.5,"publicationDate":"2025-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143724695","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}