Thomas H. Burbine, Iman Khanani, Deepika Kumawat, Ahlay Hussain, Sydney M. Wallace, M. Darby Dyar
The most widely used method to spectrally classify asteroids is the Bus–DeMeo taxonomy. To test how well the Bus–DeMeo taxonomy groups asteroids on the basis of their mineralogy, we have classified ∼1500 meteorite spectra using this Bus–DeMeo system. Some asteroid classes group together meteorites with similar compositions better than others. Howardite, eucrite, and diogenite spectra tend to be classified as V-types, while ordinary chondrite spectra tend to be classified as S-complex or Q-type bodies. The relatively featureless D- and X-types tend to be dominated by CM carbonaceous chondrites but with a substantial number of matches also with iron meteorites. The large proportion of CM chondrite matches for the D- and X-classes is most likely due to the large number of CM chondrite spectra and the rarity of spectra of more fragile carbonaceous chondrites in our data set. A number of relatively featureless asteroid classes like the C-, B-, L-, and Xc-types group meteorite types together with a wide variety of mineralogies and thermal histories. Visual albedos are vital for distinguishing between many of these assemblages. The Bus–DeMeo taxonomy does have trouble classifying olivine-dominated meteorites that do not have red-sloped spectra because this type of spectrum is rare among asteroids. For many asteroid classes, care must be used when making mineralogical interpretations based solely on spectral type.
最广泛使用的小行星光谱分类方法是 Bus-DeMeo 分类法。为了测试 Bus-DeMeo 分类法根据矿物学对小行星进行分类的效果，我们使用 Bus-DeMeo 系统对 1500 ∼ 1500 颗陨石的光谱进行了分类。有些小行星类别能比其他类别更好地将成分相似的陨石组合在一起。霍华德石、白云石和透辉石的光谱倾向于被归类为 V 型，而普通的软玉光谱则倾向于被归类为 S 复合型或 Q 型体。相对无特征的 D 型和 X 型往往以 CM 碳质软玉为主，但也有相当数量的铁陨石。D 类和 X 类中与 CM 类软玉体匹配的比例较大，这很可能是由于我们的数据集中有大量 CM 类软玉体的光谱，而较脆弱的碳质软玉体的光谱则很少。一些相对无特征的小行星类别，如 C-类、B-类、L-类和 Xc-类，将各种矿物学和热历史的陨石类型组合在一起。目视反照率对于区分其中许多组合至关重要。Bus-DeMeo 分类法在对没有红色倾斜光谱的橄榄石为主的陨石进行分类时确实会遇到困难，因为这种类型的光谱在小行星中很少见。对于许多小行星类别，在仅根据光谱类型进行矿物学解释时必须小心谨慎。
{"title":"Testing the Bus–DeMeo Asteroid Taxonomy Using Meteorite Spectra","authors":"Thomas H. Burbine, Iman Khanani, Deepika Kumawat, Ahlay Hussain, Sydney M. Wallace, M. Darby Dyar","doi":"10.3847/psj/ad57b6","DOIUrl":"https://doi.org/10.3847/psj/ad57b6","url":null,"abstract":"The most widely used method to spectrally classify asteroids is the Bus–DeMeo taxonomy. To test how well the Bus–DeMeo taxonomy groups asteroids on the basis of their mineralogy, we have classified ∼1500 meteorite spectra using this Bus–DeMeo system. Some asteroid classes group together meteorites with similar compositions better than others. Howardite, eucrite, and diogenite spectra tend to be classified as V-types, while ordinary chondrite spectra tend to be classified as S-complex or Q-type bodies. The relatively featureless D- and X-types tend to be dominated by CM carbonaceous chondrites but with a substantial number of matches also with iron meteorites. The large proportion of CM chondrite matches for the D- and X-classes is most likely due to the large number of CM chondrite spectra and the rarity of spectra of more fragile carbonaceous chondrites in our data set. A number of relatively featureless asteroid classes like the C-, B-, L-, and Xc-types group meteorite types together with a wide variety of mineralogies and thermal histories. Visual albedos are vital for distinguishing between many of these assemblages. The Bus–DeMeo taxonomy does have trouble classifying olivine-dominated meteorites that do not have red-sloped spectra because this type of spectrum is rare among asteroids. For many asteroid classes, care must be used when making mineralogical interpretations based solely on spectral type.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"53 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142200984","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Small planetary bodies in the solar system, including Io, Ganymede, and Callisto, may have a crust denser than their underlying mantle. Despite the inherent gravitational instability of such structures, we show that the growth timescale of the Rayleigh–Taylor (RT) instability can be as long as the age of the solar system, owing to the strong temperature dependence of viscosity. Even in cases where the instability timescale is shorter, the instability is confined to a thin layer at the base of the crust, making the foundering of the entire crust improbable in many scenarios. This study delineates the onset and aftermath of the RT instability, applying a quantitative framework to assess the stability of (i) rock-contaminated crust on icy satellites, and (ii) silicate crust floating on top of a subsurface magma ocean on Io. Notably, for Io the RT instability peels off only 10–100 m from the crust’s base, and thermal diffusion rapidly recovers the crustal thickness through solidification of a magma ocean. Despite recurrent delamination of the crustal base, the initial crustal thickness is maintained by thermal diffusion, virtually stabilizing a floating dense crust. Cracking of the crust also is unlikely to result in the foundering of the crust. A dense crust on a small body is therefore difficult to be overturned, suggesting the potential ubiquity of dense surface layers throughout the solar system.
{"title":"The Stability of a Dense Crust Situated on Small Bodies","authors":"Yoshinori Miyazaki, David J. Stevenson","doi":"10.3847/psj/ad65d2","DOIUrl":"https://doi.org/10.3847/psj/ad65d2","url":null,"abstract":"Small planetary bodies in the solar system, including Io, Ganymede, and Callisto, may have a crust denser than their underlying mantle. Despite the inherent gravitational instability of such structures, we show that the growth timescale of the Rayleigh–Taylor (RT) instability can be as long as the age of the solar system, owing to the strong temperature dependence of viscosity. Even in cases where the instability timescale is shorter, the instability is confined to a thin layer at the base of the crust, making the foundering of the entire crust improbable in many scenarios. This study delineates the onset and aftermath of the RT instability, applying a quantitative framework to assess the stability of (i) rock-contaminated crust on icy satellites, and (ii) silicate crust floating on top of a subsurface magma ocean on Io. Notably, for Io the RT instability peels off only 10–100 m from the crust’s base, and thermal diffusion rapidly recovers the crustal thickness through solidification of a magma ocean. Despite recurrent delamination of the crustal base, the initial crustal thickness is maintained by thermal diffusion, virtually stabilizing a floating dense crust. Cracking of the crust also is unlikely to result in the foundering of the crust. A dense crust on a small body is therefore difficult to be overturned, suggesting the potential ubiquity of dense surface layers throughout the solar system.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"16 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142200980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Post-Cassini ring seismology analysis suggests the existence of a stable stratification inside Saturn that extends from the center to ∼60% of its radius, in what is recognized today as Saturn’s dilute core. Similarly, gravity measurements on Jupiter suggest the existence of a dilute core of weekly constrained radial extent. These cores are likely in a double-diffusive regime, which prompts the question of their long-term stability. Indeed, previous direct numerical simulation (DNS) studies in triply periodic domains have shown that, in some regimes, double-diffusive convection tends to spontaneously form shallow convective layers, which coarsen until the region becomes fully convective. In this paper, we study the conditions for layering in double-diffusive convection using different boundary conditions, in which temperature and composition fluxes are fixed at the domain boundaries. We run a suite of DNSs varying microscopic diffusivities of the fluid and the strength of the initial stratification. We find that convective layers still form as a result of the previously discovered γ-instability, which takes place whenever the local stratification drops below a critical threshold that only depends on the fluid diffusivities. We also find that the layers grow once formed, eventually occupying the entire domain. Our work thus recovers the results of previous studies, despite the new boundary conditions, suggesting that this behavior is universal. The existence of Saturn’s stably stratified core, today, therefore suggests that this threshold has never been reached, which places a new constraint on scenarios for the planet’s formation and evolution.
{"title":"Constraints on the Long-term Existence of Dilute Cores in Giant Planets","authors":"A. Tulekeyev, P. Garaud, B. Idini, J. J. Fortney","doi":"10.3847/psj/ad6571","DOIUrl":"https://doi.org/10.3847/psj/ad6571","url":null,"abstract":"Post-Cassini ring seismology analysis suggests the existence of a stable stratification inside Saturn that extends from the center to ∼60% of its radius, in what is recognized today as Saturn’s dilute core. Similarly, gravity measurements on Jupiter suggest the existence of a dilute core of weekly constrained radial extent. These cores are likely in a double-diffusive regime, which prompts the question of their long-term stability. Indeed, previous direct numerical simulation (DNS) studies in triply periodic domains have shown that, in some regimes, double-diffusive convection tends to spontaneously form shallow convective layers, which coarsen until the region becomes fully convective. In this paper, we study the conditions for layering in double-diffusive convection using different boundary conditions, in which temperature and composition fluxes are fixed at the domain boundaries. We run a suite of DNSs varying microscopic diffusivities of the fluid and the strength of the initial stratification. We find that convective layers still form as a result of the previously discovered <italic toggle=\"yes\">γ</italic>-instability, which takes place whenever the local stratification drops below a critical threshold that only depends on the fluid diffusivities. We also find that the layers grow once formed, eventually occupying the entire domain. Our work thus recovers the results of previous studies, despite the new boundary conditions, suggesting that this behavior is universal. The existence of Saturn’s stably stratified core, today, therefore suggests that this threshold has never been reached, which places a new constraint on scenarios for the planet’s formation and evolution.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"34 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142200983","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Emileigh S. Shoemaker, Titus M. Casademont, Lynn M. Carter, Patrick Russell, Henning Dypvik, Sanna Alwmark, Briony H. N. Horgan, Hans E. F. Amundsen, Sigurd Eide, Svein-Erik Hamran, David A. Paige, Sanjeev Gupta, Emily L. Cardarelli, Uni Árting, Tor Berger, Sverre Brovoll
Perseverance traversed the eastern, northern, and western margins of the Séítah formation inlier on the rover’s western fan front approach. Mapping the stratigraphy and extent of the Máaz and Séítah formations is key to understanding the depositional history and timing of crater floor resurfacing events. Perseverance's rapid progress across the Jezero crater floor between the Octavia E. Butler landing site and the western fan front resulted in limited contextual images of the deposits from the Navigation Camera and Mast Camera Zoom. By combining the limited surface images with continuous subsurface sounding by the Radar Imager for Mars’ Subsurface Experiment (RIMFAX) ground-penetrating radar, Jezero crater floor stratigraphy was inferred along this rapid traverse. We produced the first subsurface map of the Máaz formation thickness and elevation of the buried Séítah formation for 2.3 km of the rapid traverse. Three distinct reflector packets were observed in RIMFAX profiles interspersed with regions of low-radar reflectivity. We interpret these reflector packets with increasing depth to be the Roubion member of the Máaz formation (covered in places with regolith), the Rochette member, and the Séítah formation. We found a median permittivity of 9.0 and bulk density of 3.2 g cm−3 from hyperbola fits to RIMFAX profiles, which suggests a mafic composition for Máaz and Séítah. The low-radar reflectivity regions within each reflector packet could indicate potential depositional hiatuses where low-density material like sediment or regolith could have accumulated between successive Máaz formation lava flows and the Séítah formation at depth.
{"title":"Observations of Igneous Subsurface Stratigraphy during the Jezero Crater Floor Rapid Traverse from the RIMFAX Ground-penetrating Radar","authors":"Emileigh S. Shoemaker, Titus M. Casademont, Lynn M. Carter, Patrick Russell, Henning Dypvik, Sanna Alwmark, Briony H. N. Horgan, Hans E. F. Amundsen, Sigurd Eide, Svein-Erik Hamran, David A. Paige, Sanjeev Gupta, Emily L. Cardarelli, Uni Árting, Tor Berger, Sverre Brovoll","doi":"10.3847/psj/ad6445","DOIUrl":"https://doi.org/10.3847/psj/ad6445","url":null,"abstract":"Perseverance traversed the eastern, northern, and western margins of the Séítah formation inlier on the rover’s western fan front approach. Mapping the stratigraphy and extent of the Máaz and Séítah formations is key to understanding the depositional history and timing of crater floor resurfacing events. Perseverance's rapid progress across the Jezero crater floor between the Octavia E. Butler landing site and the western fan front resulted in limited contextual images of the deposits from the Navigation Camera and Mast Camera Zoom. By combining the limited surface images with continuous subsurface sounding by the Radar Imager for Mars’ Subsurface Experiment (RIMFAX) ground-penetrating radar, Jezero crater floor stratigraphy was inferred along this rapid traverse. We produced the first subsurface map of the Máaz formation thickness and elevation of the buried Séítah formation for 2.3 km of the rapid traverse. Three distinct reflector packets were observed in RIMFAX profiles interspersed with regions of low-radar reflectivity. We interpret these reflector packets with increasing depth to be the Roubion member of the Máaz formation (covered in places with regolith), the Rochette member, and the Séítah formation. We found a median permittivity of 9.0 and bulk density of 3.2 g cm<sup>−3</sup> from hyperbola fits to RIMFAX profiles, which suggests a mafic composition for Máaz and Séítah. The low-radar reflectivity regions within each reflector packet could indicate potential depositional hiatuses where low-density material like sediment or regolith could have accumulated between successive Máaz formation lava flows and the Séítah formation at depth.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142200981","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Melissa D. Lane, Edward A. Cloutis, Roger N. Clark, M. Darby Dyar, Joern Helbert, Amanda R. Hendrix, Gregory Holsclaw, Alessandro Maturilli, Neil Pearson, Mikki Osterloo, Faith Vilas, Daniel Applin
This paper presents far-ultraviolet through mid-infrared (0.12–20 μm) reflectance spectra of 27 fine-particulate (<10 μm) terrestrial mineral samples, providing continuous spectra that cover an unusually broad spectral range and are of unusually fine particle size relative to most existing spectral libraries. These spectra of common geologic materials are useful for future applications that study the dust on various planetary bodies. Reflectance spectra were acquired of the samples at multiple laboratories at multiple wavelengths. All of the spectra were compared to one another to observe the general, common spectral characteristics (e.g., slope, band shape, and band depth), and the best segments of the spectra representing the mineral reflectance were scaled and spliced together to form a “Frankenspectrum” for each mineral that best represents the full wavelength range of far-ultraviolet, visible, near-infrared, and middle-infrared wavelengths. These scaled and spliced Frankenspectra, as well as the entire set of individual “original” reflectance spectra from each laboratory, are available in the Planetary Data System Geosciences Node.
本文展示了 27 个细粒度（10 μm）陆地矿物样本的远紫外至中红外（0.12-20 μm）反射光谱，提供的连续光谱覆盖了异常宽的光谱范围，与大多数现有光谱库相比，其粒度异常细小。这些常见地质材料的光谱对于未来研究各种行星体上尘埃的应用非常有用。在多个实验室采集了样品在多个波长下的反射光谱。对所有光谱进行相互比较，以观察一般的、共同的光谱特征（如斜率、波段形状和波段深度），并将代表矿物反射率的最佳光谱段按比例放大和拼接，以形成每种矿物的 "弗兰克光谱"，该光谱最能代表远紫外、可见光、近红外和中红外波长的全部波长范围。这些经过缩放和拼接的弗兰肯光谱，以及来自每个实验室的一整套单独的 "原始 "反射光谱，都可以在行星数据系统地球科学节点（Planetary Data System Geosciences Node）中找到。
{"title":"Reflectance Spectroscopy of 27 Fine-particulate Mineral Samples from Far-ultraviolet through Mid-infrared (0.12–20 μm)","authors":"Melissa D. Lane, Edward A. Cloutis, Roger N. Clark, M. Darby Dyar, Joern Helbert, Amanda R. Hendrix, Gregory Holsclaw, Alessandro Maturilli, Neil Pearson, Mikki Osterloo, Faith Vilas, Daniel Applin","doi":"10.3847/psj/ad5af7","DOIUrl":"https://doi.org/10.3847/psj/ad5af7","url":null,"abstract":"This paper presents far-ultraviolet through mid-infrared (0.12–20 <italic toggle=\"yes\">μ</italic>m) reflectance spectra of 27 fine-particulate (<10 <italic toggle=\"yes\">μ</italic>m) terrestrial mineral samples, providing continuous spectra that cover an unusually broad spectral range and are of unusually fine particle size relative to most existing spectral libraries. These spectra of common geologic materials are useful for future applications that study the dust on various planetary bodies. Reflectance spectra were acquired of the samples at multiple laboratories at multiple wavelengths. All of the spectra were compared to one another to observe the general, common spectral characteristics (e.g., slope, band shape, and band depth), and the best segments of the spectra representing the mineral reflectance were scaled and spliced together to form a “Frankenspectrum” for each mineral that best represents the full wavelength range of far-ultraviolet, visible, near-infrared, and middle-infrared wavelengths. These scaled and spliced Frankenspectra, as well as the entire set of individual “original” reflectance spectra from each laboratory, are available in the Planetary Data System Geosciences Node.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"61 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142225759","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Martian atmospheric Ne may reflect recent gas supply from its mantle via volcanic degassing, due to its short (∼100 Myr) escape timescale. The isotopic ratio of the Martian atmospheric Ne would therefore provide insights into that of the Martian mantle, further suggesting the origin of Mars volatiles during planetary formation. Mass spectrometric analysis of the Martian atmospheric Ne, however, has faced challenges from interference between 20Ne+ and 40Ar++. Previous studies using a polyimide membrane for 20Ne/40Ar separation were limited by the drawbacks of elastomeric O-rings to support the membrane, such as low-temperature intolerance, outgassing, and the need to endure environmental conditions during the launch and before/after landing on Mars. This study proposes a new method employing a metal C-ring to secure a 100 μm polyimide sheet within vacuum flanges. Environmental tests, including vibration, shock, extreme temperatures, and radiation exposure, were conducted on the gas separation flanges. Pre- and post-test analyses for He, Ne, and Ar demonstrated the membrane-flange system’s resilience. Gas permeation measurements using terrestrial air effectively permeated 4He and 20Ne, while reducing 40Ar by more than six orders of magnitude. This study achieved a <3% accuracy in determining the 20Ne/22Ne ratio, sufficient for assessing the origins of Ne in the Martian mantle. Furthermore, experiments with a 590 Pa gas mixture simulating the Martian atmosphere achieved a 10% accuracy for the 20Ne/22Ne isotope ratio, with gas abundances consistent with numerical predictions based on individual partial pressures. These results validate the suitability of the developed polyimide membrane assembly for in situ Martian Ne analyses.
火星大气中的 "氖 "可能反映了最近通过火山脱气从火星地幔中获得的气体，因为 "氖 "的逃逸时间很短（100 Myr）。因此，火星大气中氖的同位素比值将有助于了解火星地幔的同位素比值，进一步说明火星挥发物在行星形成过程中的来源。然而，火星大气中 Ne 的质谱分析面临着 20Ne+ 和 40Ar++ 之间干扰的挑战。以前使用聚酰亚胺膜来分离 20Ne/40Ar 的研究受到了支撑膜的弹性 O 形环的缺点的限制，如不耐低温、排气，以及在发射过程中和登陆火星前后需要承受环境条件等。本研究提出了一种采用金属 C 形环将 100 μm 聚酰亚胺薄膜固定在真空法兰内的新方法。对气体分离法兰进行了环境测试，包括振动、冲击、极端温度和辐射暴露。对 He、Ne 和 Ar 进行的试验前和试验后分析表明，膜-法兰系统具有良好的适应性。使用陆地空气进行的气体渗透测量有效地渗透了 4He 和 20Ne，同时将 40Ar 减少了六个数量级以上。这项研究在确定20Ne/22Ne比率方面达到了<3%的精确度，足以评估火星地幔中Ne的来源。此外，使用模拟火星大气的 590 Pa 气体混合物进行的实验使 20Ne/22Ne 同位素比值的精确度达到了 10%，气体丰度与基于单个分压的数值预测一致。这些结果验证了所开发的聚酰亚胺膜组件适用于原位火星氖分析。
{"title":"Validation Experiments for In Situ Ne Isotope Analysis on Mars: Gas Separation Flange Assembly Using Polyimide Membrane and Metal Seal","authors":"Yuichiro Cho, Yayoi N. Miura, Hikaru Hyuga, Kenta Shimokoshi, Kazuo Yoshioka, Hiroyuki Kurokawa, Hidenori Kumagai, Naoyoshi Iwata, Satoshi Kasahara, Haruhisa Tabata, Mari Aida, Yoshifumi Saito, Seiji Sugita","doi":"10.3847/psj/ad66ba","DOIUrl":"https://doi.org/10.3847/psj/ad66ba","url":null,"abstract":"The Martian atmospheric Ne may reflect recent gas supply from its mantle via volcanic degassing, due to its short (∼100 Myr) escape timescale. The isotopic ratio of the Martian atmospheric Ne would therefore provide insights into that of the Martian mantle, further suggesting the origin of Mars volatiles during planetary formation. Mass spectrometric analysis of the Martian atmospheric Ne, however, has faced challenges from interference between <sup>20</sup>Ne<sup>+</sup> and <sup>40</sup>Ar<sup>++</sup>. Previous studies using a polyimide membrane for <sup>20</sup>Ne/<sup>40</sup>Ar separation were limited by the drawbacks of elastomeric O-rings to support the membrane, such as low-temperature intolerance, outgassing, and the need to endure environmental conditions during the launch and before/after landing on Mars. This study proposes a new method employing a metal C-ring to secure a 100 <italic toggle=\"yes\">μ</italic>m polyimide sheet within vacuum flanges. Environmental tests, including vibration, shock, extreme temperatures, and radiation exposure, were conducted on the gas separation flanges. Pre- and post-test analyses for He, Ne, and Ar demonstrated the membrane-flange system’s resilience. Gas permeation measurements using terrestrial air effectively permeated <sup>4</sup>He and <sup>20</sup>Ne, while reducing <sup>40</sup>Ar by more than six orders of magnitude. This study achieved a <3% accuracy in determining the <sup>20</sup>Ne/<sup>22</sup>Ne ratio, sufficient for assessing the origins of Ne in the Martian mantle. Furthermore, experiments with a 590 Pa gas mixture simulating the Martian atmosphere achieved a 10% accuracy for the <sup>20</sup>Ne/<sup>22</sup>Ne isotope ratio, with gas abundances consistent with numerical predictions based on individual partial pressures. These results validate the suitability of the developed polyimide membrane assembly for in situ Martian Ne analyses.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"26 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142200986","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Impact crater formation is affected by the physical properties of planetary crusts, allowing comparison of crater dimensions to serve as a proxy for comparing the crustal properties of different planetary bodies. New topographic profiles of Callisto craters, derived from Galileo-based digital terrain models, are presented, and the crater dimensions recorded. These data were used to derive crater morphometry scaling trends, which were then compared to the established trends of Ganymede and the Moon. Our comparative study suggests that the upper brittle portion of Callisto’s ice crust allows for the retention of steep-sided and elevated rim scarps, while subsurface warmer ice leads to an enhanced uplift and shallowing of the crater bowl. Crater dimensions are similar between Callisto and Ganymede, suggesting that the bulk properties of their near-surface crusts are comparable. The most notable difference between craters on these two Galilean moons were the smaller central pit diameters on Callisto. This difference can be explained if the pit formation on these bodies is controlled by the presence and movement (drainage and/or volatile loss) of impact melt water: the lower impact velocity and/or lower expected crustal heat flow on Callisto will result in less impact melt generation, and thus smaller central pits.
{"title":"Crater Morphometry on Callisto","authors":"V. J. Bray, P. M. Schenk","doi":"10.3847/psj/ad61dd","DOIUrl":"https://doi.org/10.3847/psj/ad61dd","url":null,"abstract":"Impact crater formation is affected by the physical properties of planetary crusts, allowing comparison of crater dimensions to serve as a proxy for comparing the crustal properties of different planetary bodies. New topographic profiles of Callisto craters, derived from Galileo-based digital terrain models, are presented, and the crater dimensions recorded. These data were used to derive crater morphometry scaling trends, which were then compared to the established trends of Ganymede and the Moon. Our comparative study suggests that the upper brittle portion of Callisto’s ice crust allows for the retention of steep-sided and elevated rim scarps, while subsurface warmer ice leads to an enhanced uplift and shallowing of the crater bowl. Crater dimensions are similar between Callisto and Ganymede, suggesting that the bulk properties of their near-surface crusts are comparable. The most notable difference between craters on these two Galilean moons were the smaller central pit diameters on Callisto. This difference can be explained if the pit formation on these bodies is controlled by the presence and movement (drainage and/or volatile loss) of impact melt water: the lower impact velocity and/or lower expected crustal heat flow on Callisto will result in less impact melt generation, and thus smaller central pits.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"166 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142200985","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Salt clouds are predicted to be common on warm exoplanets, but their optical properties are uncertain. The Exoplanet Cloud Ensemble Scattering System (ExCESS), a new apparatus to measure the scattering intensity and degree of linear polarization for an ensemble of particles, is introduced here and used to study the light scattering properties of KCl cloud analogs. ExCESS illuminates particles with a polarized laser beam (532 nm) and uses a photomultiplier tube detector to sweep the plane of illumination. Scattering measurements for KCl particles were collected for three size distributions representative of modeled clouds for the warm exoplanet GJ 1214b. Our measurements show that Lorenz–Mie calculations, commonly used to estimate the light scattering properties of assumedly spherical cloud particles, offer an inaccurate depiction of cubic and cuboid KCl particles. All of our measurements indicate that Lorenz–Mie scattering overestimates the backscattering intensity of our cloud analogs and incorrectly predicts the scattering at mid-phase angles (∼90°) and the preferential polarization state of KCl scattered light. Our results align with the general scattering properties of nonspherical particles and underscore the importance of further understanding the effects that such particles will have on radiative transfer models of exoplanet atmospheres and reflected light observations of exoplanets by the upcoming Nancy Grace Roman Space Telescope and Habitable Worlds Observatory.
{"title":"Light Scattering Measurements of KCl Particles as an Exoplanet Cloud Analog","authors":"Colin D. Hamill, Alexandria V. Johnson, Peter Gao","doi":"10.3847/psj/ad6569","DOIUrl":"https://doi.org/10.3847/psj/ad6569","url":null,"abstract":"Salt clouds are predicted to be common on warm exoplanets, but their optical properties are uncertain. The Exoplanet Cloud Ensemble Scattering System (ExCESS), a new apparatus to measure the scattering intensity and degree of linear polarization for an ensemble of particles, is introduced here and used to study the light scattering properties of KCl cloud analogs. ExCESS illuminates particles with a polarized laser beam (532 nm) and uses a photomultiplier tube detector to sweep the plane of illumination. Scattering measurements for KCl particles were collected for three size distributions representative of modeled clouds for the warm exoplanet GJ 1214b. Our measurements show that Lorenz–Mie calculations, commonly used to estimate the light scattering properties of assumedly spherical cloud particles, offer an inaccurate depiction of cubic and cuboid KCl particles. All of our measurements indicate that Lorenz–Mie scattering overestimates the backscattering intensity of our cloud analogs and incorrectly predicts the scattering at mid-phase angles (∼90°) and the preferential polarization state of KCl scattered light. Our results align with the general scattering properties of nonspherical particles and underscore the importance of further understanding the effects that such particles will have on radiative transfer models of exoplanet atmospheres and reflected light observations of exoplanets by the upcoming Nancy Grace Roman Space Telescope and Habitable Worlds Observatory.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142200987","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Because of radiogenic processes, the lunar interior is a source of rare gases like helium (4He), argon (40Ar), and radon (222Rn) that might be released continuously, or impulsively during moonquakes. The detection of radon is therefore important in the sense that it can help trace the crustal dynamics on the Moon. In this study, we will introduce a Monte Carlo–based model designed to investigate the time-dependent transient dynamics of the lunar 222Rn exosphere. Our model accounts for the background emission and transient ejection of gas molecules from the lunar surface, encompassing loss processes such as radioactive decay, photoionization, and the cold trapping in permanently shadowed regions near the poles. Additionally, it incorporates the diurnal temperature fluctuations of the lunar surface, which significantly influence the condensation duration of the radon atoms and their subsequent release near the sunrise. This model also can support future observations in missions such as Chang’E 6 or other lunar explorations.
{"title":"Temporal Variations of 222Rn Density Distributions in the Lunar Exosphere","authors":"Ian-Lin Lai, Wing-Huen Ip","doi":"10.3847/psj/ad698e","DOIUrl":"https://doi.org/10.3847/psj/ad698e","url":null,"abstract":"Because of radiogenic processes, the lunar interior is a source of rare gases like helium (<sup>4</sup>He), argon (<sup>40</sup>Ar), and radon (<sup>222</sup>Rn) that might be released continuously, or impulsively during moonquakes. The detection of radon is therefore important in the sense that it can help trace the crustal dynamics on the Moon. In this study, we will introduce a Monte Carlo–based model designed to investigate the time-dependent transient dynamics of the lunar <sup>222</sup>Rn exosphere. Our model accounts for the background emission and transient ejection of gas molecules from the lunar surface, encompassing loss processes such as radioactive decay, photoionization, and the cold trapping in permanently shadowed regions near the poles. Additionally, it incorporates the diurnal temperature fluctuations of the lunar surface, which significantly influence the condensation duration of the radon atoms and their subsequent release near the sunrise. This model also can support future observations in missions such as Chang’E 6 or other lunar explorations.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142200765","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Apophis’s current trajectory takes it safely past our planet at a distance of several Earth radii on 2029 April 13. Here the possibility is considered that Apophis could collide with a small asteroid, like the ones that frequently and unpredictably strike Earth, and the resulting perturbation of its trajectory. The probability of an impact that could significantly displace Apophis relative to its keyholes is found to be less than one in 106, requiring a Δv ≳ 0.3 mm s−1, while for an impact that could significantly displace Apophis compared to its miss distance in 2029, it is less than one in 109, requiring a Δv ≳ 5 cm s−1. These probabilities are below the usual thresholds considered by asteroid impact warning systems. Apophis is in the daytime sky and unobservable from mid-2021 to 2027. It will be challenging to determine from single-night observations in 2027 if Apophis has moved on the target plane enough to enter a dangerous keyhole, as the deviation from the nominal ephemeris might be only a few tenths of an arcsecond. An impending Earth impact would, however, be signaled clearly in most cases by deviations of tens of arcseconds of Apophis from its nominal ephemeris in 2027. Thus, most of the impact risk could be retired by a single observation of Apophis in 2027, though a minority of cases present some ambiguity and are discussed in more detail. Charts of the on-sky position of Apophis under different scenarios are presented for quick assessment by observers.
{"title":"On the Sensitivity of Apophis’s 2029 Earth Approach to Small Asteroid Impacts","authors":"Paul Wiegert","doi":"10.3847/psj/ad644d","DOIUrl":"https://doi.org/10.3847/psj/ad644d","url":null,"abstract":"Apophis’s current trajectory takes it safely past our planet at a distance of several Earth radii on 2029 April 13. Here the possibility is considered that Apophis could collide with a small asteroid, like the ones that frequently and unpredictably strike Earth, and the resulting perturbation of its trajectory. The probability of an impact that could significantly displace Apophis relative to its keyholes is found to be less than one in 10<sup>6</sup>, requiring a Δ<italic toggle=\"yes\">v</italic> ≳ 0.3 mm s<sup>−1</sup>, while for an impact that could significantly displace Apophis compared to its miss distance in 2029, it is less than one in 10<sup>9</sup>, requiring a Δ<italic toggle=\"yes\">v</italic> ≳ 5 cm s<sup>−1</sup>. These probabilities are below the usual thresholds considered by asteroid impact warning systems. Apophis is in the daytime sky and unobservable from mid-2021 to 2027. It will be challenging to determine from single-night observations in 2027 if Apophis has moved on the target plane enough to enter a dangerous keyhole, as the deviation from the nominal ephemeris might be only a few tenths of an arcsecond. An impending Earth impact would, however, be signaled clearly in most cases by deviations of tens of arcseconds of Apophis from its nominal ephemeris in 2027. Thus, most of the impact risk could be retired by a single observation of Apophis in 2027, though a minority of cases present some ambiguity and are discussed in more detail. Charts of the on-sky position of Apophis under different scenarios are presented for quick assessment by observers.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142200766","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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