Icarus最新文献

{"title":"Decameter-sized Earth impactors – I: Orbital properties","authors":"Ian Chow ,&nbsp;Peter G. Brown","doi":"10.1016/j.icarus.2024.116444","DOIUrl":"10.1016/j.icarus.2024.116444","url":null,"abstract":"<div><div>Numerous decameter-sized asteroids have been observed impacting Earth as fireballs. These objects can have impact energies equivalent to hundreds of kilotons of TNT, posing a hazard if they impact populated areas. Previous estimates of meteoroid flux using fireball observations have shown an Earth impact rate for decameter-size objects of about once every 2–3 years. In contrast, telescopic estimates of the near-Earth asteroid population predict the impact rate of such objects to be of order 20–40 years, an order-of-magnitude difference. While the cause of this discrepancy remains unclear, tidal disruption of a larger near-Earth body has been proposed as an explanation for these excess decameter-sized impactors. The release in 2022 of previously classified United States Government (USG) satellite sensor data for fireball events has provided a wealth of new information on many of these impacts. Using this newly available USG sensor data, we present the first population-level study characterizing the orbital and dynamical properties of 14 decameter-sized Earth impactors detected by USG sensors since 1994, with a particular focus on searching for evidence of tidal disruption as the cause of the impact rate discrepancy. We find there is no evidence for recent (<span><math><mrow><mo>≲</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>4</mn></mrow></msup></mrow></math></span> years) tidal disruption and weak evidence for longer-term tidal disruption in the decameter impactor population, but that the latter conclusion is limited by small number statistics. We also investigate the origins of both the impactor and near-Earth asteroid populations of decameter-sized objects from the main asteroid belt. We find that both populations generally originate from the same source regions: primarily from the <span><math><msub><mrow><mi>ν</mi></mrow><mrow><mn>6</mn></mrow></msub></math></span> secular resonance (<span><math><mrow><mo>∼</mo><mn>70</mn></mrow></math></span>%) with small contributions from the Hungaria group (<span><math><mrow><mo>∼</mo><mn>20</mn></mrow></math></span>%) and the 3:1 Jupiter mean-motion resonance (<span><math><mrow><mo>∼</mo><mn>10</mn></mrow></math></span>%).</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116444"},"PeriodicalIF":2.5,"publicationDate":"2024-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134795","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":"The curious case of the missing mantle: How carbonaceous chondrites may confound the spectral identification of partially differentiated asteroids","authors":"C.D. Schultz,&nbsp;R.E. Milliken","doi":"10.1016/j.icarus.2024.116442","DOIUrl":"10.1016/j.icarus.2024.116442","url":null,"abstract":"<div><div>The scarcity of olivine-rich mantle material in meteorite collections and asteroid spectra, known as the “Missing Mantle Conundrum,” challenges our understanding of planetesimal differentiation. Current models suggest that numerous planetesimals underwent melting and differentiation early in Solar System history, yet little evidence of olivine- and pyroxene-rich mantles is found. We explore the hypothesis that mantle material may be present in the asteroid belt but is spectrally masked by dark, primitive carbonaceous chondrite material. To test this, we mixed laboratory analogs of CM and CV chondrite mantle compositions with natural CM2 and CV3 meteorites, examining how particle size and chondritic material abundance affect the detectability of diagnostic silicate absorption features. Visible-near infrared (VNIR) reflectance spectra demonstrate that even small amounts of carbonaceous material can suppress olivine and pyroxene absorption bands. The suppression of absorption features and spectral darkening is highly nonlinear, with this effect being most notable for the finer particles and the CM chondrites. At mantle abundances below 20 wt%, spectral features for all mixtures become virtually indistinguishable from those of the chondrite meteorites. Simulated noise levels typical of ground-based telescopic observations reveal that mantle material can be masked at even higher abundances, potentially obscuring ∼30–65 wt% of mantle material. These findings suggest that significant amounts of olivine- and pyroxene-rich mantle material may be present in near-Earth and main-belt asteroids, currently classified as primitive bodies. Rubble pile asteroids, which are widespread, may be particularly susceptible to misinterpretation due to their complex regolith, where differentiated mantle material can be mixed with primitive, undifferentiated components. This mixing, which arises naturally through the Solar System's ongoing collisional evolution, complicates spectral interpretations and highlights the potential for underestimating the extent of differentiation in these bodies.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116442"},"PeriodicalIF":2.5,"publicationDate":"2024-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134797","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":"Discovery of a highly shocked alkali suite clast in the Chang'e-5 lunar soils","authors":"Mengfan Qiu ,&nbsp;Sen Hu ,&nbsp;Huicun He ,&nbsp;Zongyu Yue ,&nbsp;Hejiu Hui ,&nbsp;Jialong Hao ,&nbsp;Ruiying Li ,&nbsp;Sheng Gou ,&nbsp;Lixin Gu ,&nbsp;Xu Tang ,&nbsp;Jinhua Li ,&nbsp;Wei Yang ,&nbsp;Hengci Tian ,&nbsp;Chi Zhang ,&nbsp;Di Zhang ,&nbsp;Qian Mao ,&nbsp;Lihui Jia ,&nbsp;Xiaoguang Li ,&nbsp;Yi Chen ,&nbsp;Shitou Wu ,&nbsp;Fuyuan Wu","doi":"10.1016/j.icarus.2024.116448","DOIUrl":"10.1016/j.icarus.2024.116448","url":null,"abstract":"<div><div>Lunar soils contain various types of components and thus are crucial for unraveling the geological and impact histories of the Moon. Little is known about the amount and source regions of the non-mare components preserved in the Chang'e-5 (CE5) lunar soils. A study of systematic identification and characterization of the non-mare components in the CE5 lunar soils was carried out in this work. A non-mare clast, displaying contrast to mare basalts, was firstly identified in the scooped CE5 lunar soils using nondestructive micro-CT investigating. Further detailed petrographic observations and analyses of mineral chemistry reveal that this non-mare clast is a highlands alkali suite (HAS). This HAS clast is mainly composed of plagioclase (46.5), pigeonite (30.9), K-Si-rich mesostasis (17.0), K-felspar (4.12), and silica (0.87) in area%, with minor ilmenite, merrillite, apatite, baddeleyite, and troilite. This clast contains high-pressure polymorph of silica, seifertite and stishovite, and is characterized by high K₂O (1.88 wt%), and low TiO₂ (0.63 wt%) and low FeO (8.36 wt%) contents. Pb-Pb dating of baddeleyite yields a date of 3913 ± 7 Ma, probably representing a plutonic event or an impact event happened on the Moon. Another ejection event is required to transport the alkali suite to the landing site of the CE5 mission postdated the emplacement of the CE5 mare basalt.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116448"},"PeriodicalIF":2.5,"publicationDate":"2024-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134723","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":"Four Mars Years of ACB Phase Function Observations from the Mars Science Laboratory Show Low Interannual and Diurnal Variability and Suggest Irregular Water–ice Crystal Geometry","authors":"A.C. Innanen,&nbsp;C.W. Hayes,&nbsp;B.E. Koch Nichol,&nbsp;J.E. Moores","doi":"10.1016/j.icarus.2024.116437","DOIUrl":"10.1016/j.icarus.2024.116437","url":null,"abstract":"<div><div>We extend previous work examining the water–ice cloud phase function to four years (Mars years 34-37) using observations taken during the Aphelion Cloud Belt season by the Mars Science Laboratory. From these phase functions, we continue to see little interannual or diurnal variability in Mars years 35-37, but potential diurnal variability in p=MY 34, which is not well understood. We use our derived phase functions to comment upon possible ice-crystal geometry by fitting a two-term Henyey–Greenstein function and comparing our results with those of modeled water–ice crystals and dust. These results suggest that cloud particles on Mars could have irregular geometry.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116437"},"PeriodicalIF":2.5,"publicationDate":"2024-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134539","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":"Impact strength of cm-to-decimeter scale weak porous targets: Implication for lifetime of boulders on asteroids","authors":"Kazuhiro Horikawa ,&nbsp;Masahiko Arakawa ,&nbsp;Minami Yasui ,&nbsp;Sunao Hasegawa","doi":"10.1016/j.icarus.2024.116449","DOIUrl":"10.1016/j.icarus.2024.116449","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The lifetime of weak porous boulders on main belt asteroids was experimentally investigated using their impact strength &lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;msub&gt;&lt;mi&gt;Q&lt;/mi&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;/msub&gt;&lt;mo&gt;∗&lt;/mo&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt;. We conducted impact disruption experiments on weak porous targets to simulate the conditions of boulders found on C-type asteroids such as Ryugu and Bennu. Projectiles made of polycarbonate and nylon were impacted on spherical targets with the diameter from 30 to 120 mm at velocities ranging from 0.6 to 6.1 kms&lt;sup&gt;−1&lt;/sup&gt;. The impact angle was normal to the target surface. We varied the target's tensile strength, denoted as &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;Y&lt;/mi&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;, and the mass of the target by more than one order of magnitude. Our findings revealed that &lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;msub&gt;&lt;mi&gt;Q&lt;/mi&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;/msub&gt;&lt;mo&gt;∗&lt;/mo&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt; increased with increasing the tensile strength, and it slightly depended on the boulders' sizes. Additionally, we observed that &lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;msub&gt;&lt;mi&gt;Q&lt;/mi&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;/msub&gt;&lt;mo&gt;∗&lt;/mo&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt; depended on impact velocity according to the scaling theory for catastrophic disruption, expressed as &lt;span&gt;&lt;math&gt;&lt;msubsup&gt;&lt;mi&gt;Q&lt;/mi&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;mo&gt;∗&lt;/mo&gt;&lt;/msubsup&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;0.15&lt;/mn&gt;&lt;msup&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;mrow&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;0.25&lt;/mn&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;msubsup&gt;&lt;mi&gt;v&lt;/mi&gt;&lt;mi&gt;i&lt;/mi&gt;&lt;mn&gt;0.53&lt;/mn&gt;&lt;/msubsup&gt;&lt;msup&gt;&lt;mfenced&gt;&lt;mfrac&gt;&lt;msub&gt;&lt;mi&gt;Y&lt;/mi&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/msub&gt;&lt;mi&gt;ρ&lt;/mi&gt;&lt;/mfrac&gt;&lt;/mfenced&gt;&lt;mn&gt;0.74&lt;/mn&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt;, where &lt;em&gt;v&lt;/em&gt;&lt;sub&gt;i&lt;/sub&gt;, &lt;em&gt;D&lt;/em&gt; and ρ represent impact velocity, target diameter and target density, respectively. We also investigated the momentum transfer efficiency, denoted as &lt;span&gt;&lt;math&gt;&lt;mi&gt;β&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;, for monolithic asteroids with weak strength. &lt;span&gt;&lt;math&gt;&lt;mi&gt;β&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; was determined for cratered targets with different tensile strengths and was found to be well scaled by a characteristic velocity, denoted as &lt;em&gt;v&lt;/em&gt;*=&lt;span&gt;&lt;math&gt;&lt;msqrt&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;Y&lt;/mi&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/msub&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;ρ&lt;/mi&gt;&lt;/mrow&gt;&lt;/msqrt&gt;&lt;/math&gt;&lt;/span&gt;, for the targets with a strength smaller than 283 kPa. The relationship obtained was &lt;span&gt;&lt;math&gt;&lt;mi&gt;β&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;msup&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;mrow&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;3.3&lt;/mn&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;msup&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;v&lt;/mi&gt;&lt;mi&gt;i&lt;/mi&gt;&lt;/msub&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;msup&gt;&lt;mi&gt;v&lt;/mi&gt;&lt;mo&gt;∗&lt;/mo&gt;&lt;/msup&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;mn&gt;1.29&lt;/mn&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt;. However, the &lt;em&gt;β&lt;/em&gt; value for the strongest target with 731 kPa did not conform to this equation. Based on these results, we estimated the lifetime of boulders on main belt asteroids with various strength and sizes. Boulders with the strength between 200 kPa and 1.7 MPa, estimated for asteroids Ryugu and Bennu, are unlikely to be disrupted in less than 10 Ma for sizes larger than 4 m. However, boulders smaller than several 10 cm may not survive longer than 10 Ma, a duration almost corresponding to the surface age of Ryugu. The boulder with the size of 160 m on aster","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116449"},"PeriodicalIF":2.5,"publicationDate":"2024-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143135204","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":"Magnetically controlled ionosphere of Mars: A model analysis with the vertical plasma drift effects","authors":"T. Majeed ,&nbsp;S.W. Bougher ,&nbsp;P. Withers ,&nbsp;S.A. Haider ,&nbsp;A. Morschhauser","doi":"10.1016/j.icarus.2024.116447","DOIUrl":"10.1016/j.icarus.2024.116447","url":null,"abstract":"<div><div>We use our 1-D chemical diffusive model to quantify the physical processes necessary to interpret the dayside ionospheric electron density profiles measured with the Mars Radio Science (MaRS) experiment onboard the Mars Express (MEX) and Radio Occultation Science Experiment (ROSE) onboard the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. The electron density profiles selected for this study represent the southern high-latitude region of Mars, where the crustal magnetic field is strong and near-vertical in orientation. These electron density measurements have shown the topside plasma distribution with unusually large electron density (N_e) scale heights presumably in response to downward accelerating solar wind electrons along magnetic field lines. We find that the photochemical control of the Martian ionosphere ceases at a height well above the ionospheric peak. To interpret the measured ionospheric structure at altitudes where plasma transport dominates, we find it is necessary to impose field-aligned vertical plasma drifts most likely caused by the motion of neutral winds. The most interesting finding of this study is that both upward (between 30 ms⁻¹ and 60 ms⁻¹) and downward (between −12 ms⁻¹ and -90 ms⁻¹) drifts are required to maintain the topside N_e distribution comparable with the measured distribution. We also find that a fixed velocity boundary condition at the upper boundary with a sizeable upward ion velocity is needed to encounter any unexpected ion accumulation in the topside ionosphere to limit the Martian ionospheric outflow. Given the complex nature of neutral dynamics and its relationship to plasma transport processes over magnetic anomalies, we consider that a simple model, such as we have developed, is still capable of yielding valuable insights relating to the neutral wind system at Mars.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116447"},"PeriodicalIF":2.5,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134724","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":"Impact of a bimodal dust distribution on the 2018 Martian global dust storm with the NASA Ames Mars global climate model","authors":"Richard A. Urata ,&nbsp;Tanguy Bertrand ,&nbsp;Melinda A. Kahre ,&nbsp;R. John Wilson ,&nbsp;Alexandre M. Kling ,&nbsp;Michael J. Wolff","doi":"10.1016/j.icarus.2024.116446","DOIUrl":"10.1016/j.icarus.2024.116446","url":null,"abstract":"<div><div>Dust plays a critical role in the Martian climate, significantly impacting heating and circulation in the atmosphere. Global dust storms (GDS) are planet-encircling extreme dust events that occur every few Mars years with the most recent one happening in 2018, Mars Year (MY) 34. While they do occur on a relatively regular basis (recent ones occurring in 2001/MY25, 2007/MY28, 2018/MY34), much is still to be learned about the processes that lead to various characteristics of dust during these storms. Global climate models (GCMs) have been useful tools to interpret various observations made during the MY34 GDS. Here, we have implemented a bimodal dust lifting scheme in the NASA Ames Mars GCM. This new method for lifting dust splits the mass and number of dust particles lifted into multiple log-normal size modes as prescribed. We ran simulations assuming a small mode of dust with an effective radius of 0.3 μm and a large mode of dust with an effective radius of 3 μm lifted from the surface, with the amount of dust lifted in each mode prescribed as a fraction of the dust to be lifted. The dust is lifted to match a Mars Year 34 climatology map (Montabone et al., 2020), then transported by the general circulation and sediments with gravity. Dust is assumed to coagulate following Bertrand et al. (2022). Coagulation was found to have the greatest effect on the small mode of dust due to the large number of small dust particles lifted in that mode. We find that using a simple bimodal dust lifting scheme transports dust to higher altitude in the model simulations of the MY34 GDS, bringing the model closer to observations of atmospheric temperature, surface temperature, tides, etc.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116446"},"PeriodicalIF":2.5,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134557","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":"Vortex crystals at Jupiter’s poles: Emergence controlled by initial small-scale turbulence","authors":"Sihe Chen ,&nbsp;Andrew P. Ingersoll ,&nbsp;Cheng Li","doi":"10.1016/j.icarus.2024.116438","DOIUrl":"10.1016/j.icarus.2024.116438","url":null,"abstract":"<div><div>At the poles of Jupiter, cyclonic vortices are clustered together in patterns made up of equilateral triangles called vortex crystals. Such patterns are seen in laboratory flows but never before in a planetary atmosphere, where the planet’s rotation and gravity add new physics. Siegelman (2022b) used a one-layer quasi-geostrophic (QG) model with an infinite radius of deformation to study the emergence of vortex crystals from small-scale turbulence, and Li (2020) showed that shielding of the vortices is important for the stability of the vortex crystals. Here we use the shallow water (SW) equations at the pole of a rotating planet to study the emergence and evolution of vortices starting from an initial random pattern of small-scale turbulence. The flow is in a single layer with a free surface whose slope produces the horizontal pressure gradient force. With the planet’s radius and rotation used to define the units, only three input parameters are needed to define the system: the mean kinetic energy of the initial turbulence, the horizontal scale of the initial turbulence, and the radius of deformation of the undisturbed fluid layer. We identified a non-dimensional number, <span><math><mrow><mi>Δ</mi><mi>h</mi><mo>/</mo><mi>h</mi></mrow></math></span>, which is related to the relative layer thickness variation of the initial turbulence and determines whether the vortex crystal or chaotic patterns emerge: Small <span><math><mrow><mi>Δ</mi><mi>h</mi><mo>/</mo><mi>h</mi></mrow></math></span> values lead to vortex crystals, and large <span><math><mrow><mi>Δ</mi><mi>h</mi><mo>/</mo><mi>h</mi></mrow></math></span> values lead to chaotic patterns. The value <span><math><mrow><mi>Δ</mi><mi>h</mi><mo>/</mo><mi>h</mi></mrow></math></span> is related to the radius of deformation as <span><math><msubsup><mrow><mi>L</mi></mrow><mrow><mi>d</mi></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msubsup></math></span>. This means that a large polar radius of deformation is positively correlated to the emergence of vortex crystals, and this implies either a polar atmosphere enriched with water or deeper roots for the vortices than previously estimated.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116438"},"PeriodicalIF":2.5,"publicationDate":"2024-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134789","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":"Adaptive sampling with PIXL on the Mars Perseverance rover","authors":"Peter R. Lawson ,&nbsp;Tanya V. Kizovski ,&nbsp;Michael M. Tice ,&nbsp;Benton C. Clark ,&nbsp;Scott J. VanBommel ,&nbsp;David R. Thompson ,&nbsp;Lawrence A. Wade ,&nbsp;Robert W. Denise ,&nbsp;Christopher M. Heirwegh ,&nbsp;W. Timothy Elam ,&nbsp;Mariek E. Schmidt ,&nbsp;Yang Liu ,&nbsp;Abigail C. Allwood ,&nbsp;Martin S. Gilbert ,&nbsp;Benjamin J. Bornstein","doi":"10.1016/j.icarus.2024.116433","DOIUrl":"10.1016/j.icarus.2024.116433","url":null,"abstract":"<div><div>Planetary rovers can use onboard data analysis to adapt their measurement plan on the fly, improving the science value of data collected between commands from Earth. This paper describes the implementation of an adaptive sampling algorithm used by PIXL, the X-ray fluorescence spectrometer of the Mars 2020 <em>Perseverance</em> rover. PIXL is deployed using the rover arm to measure X-ray spectra of rocks with a scan density of several thousand points over an area of typically 5 × 7 mm. The adaptive sampling algorithm is programmed to recognize points of interest and to increase the signal-to-noise ratio at those locations by performing longer integrations. Two approaches are used to formulate the sampling rules based on past quantification data: (1) Expressions that isolate particular regions within a ternary compositional diagram, and (2) Machine learning rules that threshold for a high weight percent of particular compounds. The design of the rulesets are outlined and the performance of the algorithm is quantified using measurements from the surface of Mars. To our knowledge, PIXL’s adaptive sampling represents the first autonomous decision-making based on real-time compositional analysis by a spacecraft on the surface of another planet.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116433"},"PeriodicalIF":2.5,"publicationDate":"2024-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134555","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":"Do icy dust aggregates break up when they pass the snow line?","authors":"Sin-iti Sirono","doi":"10.1016/j.icarus.2024.116430","DOIUrl":"10.1016/j.icarus.2024.116430","url":null,"abstract":"<div><div>Icy dust aggregates can break up when they pass the snow line or when a heating event occurs because of the sublimation of H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O ice. However, the original aggregate may absorb the fragment conducting the Brownian motion because the thickness of the icy mantle of a grain is less than the typical grain radius of <span><math><mrow><mo>∼</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup><mspace></mspace></mrow></math></span>cm. On the other hand, the vapor pressure caused by the sublimated H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O molecules accelerates the fragment to escape. Rotation of the aggregate and electrostatic repulsion may also promote the escape of the fragment aggregate. Here, I determined a lower bound of the escaping fragment radius, including the effects of the vapor pressure, rotation, and electrostatic repulsion. It has been found that the breakup to the single grain does not occur, and the fragment radius strongly depends on the thickness of the icy mantle. The vapor pressure and the rotation produce fragments from large aggregates. The fragments escape from small aggregates by the electrostatic repulsion. Possible consequences of the breakup are discussed.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116430"},"PeriodicalIF":2.5,"publicationDate":"2024-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134775","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}