IF 2.5 2区物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS

Icarus

Pub Date : 2024-10-29 DOI: 10.1016/j.icarus.2024.116362

Yiheng Li , Zaicong Wang , Yuqi Qian , Wen Zhang , Yantong Feng , Hong Liu , Keqing Zong , Qi He , Zhenbing She , Xiang Wu , Ming Li , Zhaochu Hu , Long Xiao , Yang Li , Frederic Moynier

Due to rapid magma cooling and extensive space weathering, significant disequilibrium crystallization and secondary modification widely occur in lunar mare basalt after its eruption on the lunar surface. In this study, we conducted bulk and in-situ Fe isotope analyses to investigate the post-eruption processes on Chang'e-5 (CE-5) samples. The CE-5 soil shows a minor elevation of δ⁵⁶Fe value (∼0.05 ‰) relative to the CE-5 basalt clasts. Correlations between Ni and Cu contents with δ⁵⁶Fe values suggest that the minor increase in the δ⁵⁶Fe from the CE-5 basalt to soil primarily occurred during evaporation caused by meteorite impacts. Such isotopic variation between CE-5 basalt and soils is notably lower than what is observed for Apollo samples and reflects the low maturity of CE-5 soils. This is consistent with the low Is/FeO value constrained by magnetic approaches. Therefore, measuring the δ⁵⁶Fe values of lunar soil is suitable to evaluate the degrees of maturity for lunar soils due to space weathering. In-situ analyses of δ⁵⁶Fe reveal significant variations in different grains of olivine (δ⁵⁶Fe: −0.57 to −0.17 ‰) and ilmenite (−0.06 to +0.42 ‰) and also in their interior (mainly for olivine). These δ⁵⁶Fe variations in minerals can be ascribed to the disequilibrium crystallization of lava flow and fast cooling, which is consistent with conclusions based on petrologic observations such as its extensive differentiation and silicate liquid immiscibility. Therefore, the post-eruption processes on the lunar surface could lead to significant variations in isotopic compositions at different scales of basalts, which in turn record the history of late-stage magma evolution and space weathering on the lunar surface.

由于岩浆的快速冷却和广泛的空间风化作用，月壤玄武岩在月面喷发后普遍发生了严重的不平衡结晶和二次改造。在本研究中，我们对嫦娥五号（CE-5）样品进行了散装和原位铁同位素分析，以研究其喷发后的过程。与嫦娥五号玄武岩碎屑相比，嫦娥五号土壤中的δ56Fe值略有升高（∼0.05 ‰）。镍和铜含量与δ56Fe值之间的相关性表明，从CE-5玄武岩到土壤的δ56Fe的微小增加主要发生在陨石撞击引起的蒸发过程中。CE-5 玄武岩和土壤之间的这种同位素变化明显低于阿波罗样本，反映了 CE-5 土壤的低成熟度。这与磁性方法得出的低Is/FeO值是一致的。因此，测量月球土壤的 δ56Fe 值适用于评估空间风化造成的月球土壤成熟度。δ56Fe的原位分析显示，橄榄石（δ56Fe：-0.57至-0.17‰）和钛铁矿（-0.06至+0.42‰）的不同晶粒及其内部（主要是橄榄石）存在显著差异。矿物中的δ56Fe变化可归因于熔岩流的不平衡结晶和快速冷却，这与根据岩石学观察得出的结论是一致的，如熔岩流的广泛分异和硅酸盐液的不溶性。因此，月球表面爆发后的过程可能导致不同尺度玄武岩同位素组成的显著变化，进而记录了月球表面后期岩浆演化和空间风化的历史。

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引用次数: 0

Three-dimensional modeling of Ganymede’s Chapman–Ferraro magnetic field and its role in subsurface ocean induction 木卫三查普曼-费拉罗磁场的三维建模及其在地表下海洋感应中的作用

IF 2.5 2区物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS

Icarus

Pub Date : 2024-10-28 DOI: 10.1016/j.icarus.2024.116356

Nawapat Kaweeyanun , Adam Masters

In April 2023, the Jupiter Icy Moons Explorer (Juice) began its journey to orbit Jupiter’s largest and only magnetic moon, Ganymede. Part of the mission’s objectives aim to verify existence of the moon’s subsurface ocean and determine its structure through its induced response to external excitation by periodically varying magnetic field. Known contributions to the excitation are those from Jupiter’s dipole (at synodic period) and quadrupole (at half-synodic period) variations, and Ganymede’s inclined eccentric orbit around Jupiter (at orbital period). We propose that Ganymede’s magnetopause, where the Chapman–Ferraro (C–F) magnetic field arises from local currents, also contributes to subsurface ocean induction. This article introduces the first three-dimensional model of the C–F field and its outputs at Ganymede’s subsurface ocean and larger magnetosphere. The field is shown to be non-uniform — strongest near upstream Ganymede’s subflow region and gradually weakening away from it. Magnetopause asymmetry due to the Jovian guide field results in largely synodic variation of the C–F field, with exceptions near Ganymede’s equator and subflow meridian where asymmetry effects are minimal and the variations are half-synodic. The C–F field amplitude is of general order

\sim 50

nT, which is significant relative to excitation from the Jovian field. Comparisons to Galileo data and magnetohydrodynamic simulation results suggest the model is useful, therefore the magnetopause effects must be considered in future induction modeling of Ganymede’s subsurface ocean ahead of the Juice mission.

2023 年 4 月，木星冰月探测器（Juice）开始了环绕木星最大也是唯一的磁性卫星-- 木卫三（Ganymede）的旅程。此次任务的部分目标是验证该卫星是否存在地表下海洋，并通过其对周期性变化磁场的外部激励的感应反应确定其结构。已知的激励作用来自木星的偶极（同步周期）和四极（半同步周期）变化，以及木卫三围绕木星的倾斜偏心轨道（轨道周期）。我们提出，木卫三的磁极顶（Chapman-Ferraro（C-F）磁场产生于当地海流）也是造成地表下海洋感应的原因。本文首次介绍了 C-F 磁场的三维模型及其在木卫三次表层海洋和较大磁层的输出。研究表明，该磁场是不均匀的--在甘耶米德子流区上游附近最强，远离子流区后逐渐减弱。木卫二导磁场造成的磁极不对称导致了 C-F 磁场的大体同步变化，但在甘耶米德赤道和亚气流子午线附近例外，那里的不对称影响最小，变化为半同步。C-F场的振幅一般为50 nT，相对于来自木卫二场的激励来说是相当大的。与伽利略数据和磁流体动力学模拟结果的比较表明，该模型是有用的，因此，在 "朱伊斯 "任务之前，在对甘耶米底层海洋进行感应建模时，必须考虑磁极效应。

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引用次数: 0

Seasonal and interannual variability of the water vapor vertical distribution in the Martian lower atmosphere 火星低层大气中水汽垂直分布的季节性和年际可变性

IF 2.5 2区物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS

Icarus

Pub Date : 2024-10-28 DOI: 10.1016/j.icarus.2024.116360

Alexey A. Pankine , Timothy H. McConnochie , Michael D. Smith

We apply a novel method to retrieve water vapor vertical distributions in the Martian atmosphere to spectra collected by the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES). The new method exploits differences in sensitivity of the daytime and nighttime TES nadir spectra to water vapor content in different parts of the lower atmosphere (0–40 km). Based on the test retrievals from simulated environments, vertical profiles of water vapor can be retrieved with accuracy ∼20–40 % depending on the season and altitude above surface. Retrievals from observations collected by the MGS TES between L_s = 135° in MY24 and L_s = 75° in MY27 enable exploration of the seasonal and interannual variabilities of the vertical distribution of water vapor. Retrieved vapor distributions and their seasonal variability are generally consistent with those predicted by a numerical circulation model. Vapor is concentrated near the surface in the northern polar region and the mid-latitudes during the northern summer (L_s = 90°). During the southern summer (L_s = 270°) vapor extends higher in the atmosphere in the southern polar region, reflecting both sublimation of the seasonal surface ice and atmospheric transport by the upper branch of the southern Hadley cell. During both equinoxes (L_s = 0° and L_s = 180°) vapor is found in the lower part of the tropical atmosphere. At the same time the retrieved vertical distributions exhibit notable interannual variability. Following the global dust storm of MY25, vapor is confined to lower altitudes in the southern polar region during the southern summer. During the southern spring in MY26 (L_s = 180°-270°) vapor extends higher in the atmosphere and mixing ratios increase faster with height at the equator and in the northern tropics. These examples suggest that Martian atmosphere may experience interannual changes in the atmospheric transport, some of which could be in response to global dust storm events.

我们对火星全球勘测器（MGS）热辐射光谱仪（TES）收集的光谱采用了一种新方法来检索火星大气中的水汽垂直分布。新方法利用了白天和夜间 TES 天底光谱对低层大气（0-40 公里）不同部分水汽含量敏感度的差异。根据模拟环境的测试检索，水汽垂直剖面的检索精度可达 20-40 %，具体取决于季节和地面高度。从 MGS TES 在 MY24 的 Ls = 135° 和 MY27 的 Ls = 75° 之间收集的观测数据中检索水汽，可以探索水汽垂直分布的季节和年际变化。检索到的水汽分布及其季节变化与数值环流模式的预测基本一致。在北部夏季（Ls = 90°），水汽主要集中在北极地区和中纬度地区的地表附近。在南半球夏季（Ls = 270°），水汽在南极地区大气中的位置较高，这既反映了季节性地表冰的升华，也反映了南哈德利小区上支的大气输送。在两个春分（Ls = 0° 和 Ls = 180°）期间，热带大气的下部都有水汽。同时，检索到的垂直分布表现出明显的年际变化。25 年全球沙尘暴之后，水汽在南部夏季被限制在南极地区的较低高度。在 MY26 的南部春季（Ls = 180°-270°），水汽在大气中延伸到更高的位置，在赤道和北部热带地区，混合比随着高度的增加而加快。这些例子表明，火星大气可能会经历大气传输的年际变化，其中一些可能是对全球沙尘暴事件的响应。

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引用次数: 0

Changes in the longitude polarization dependence of Jupiter's moon Io as evidence of the long-term variability of its volcanic activity 木星卫星木卫一经度极化依赖性的变化是其火山活动长期变化的证据

IF 2.5 2区物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS

Icarus

Pub Date : 2024-10-24 DOI: 10.1016/j.icarus.2024.116351

Nikolai N. Kiselev , Herman G. Dyachenko , Nikolai V. Karpov , Kirill A. Antoniuk

The aim of the work was to investigate the longitude (orbital) dependence of the polarization of Jupiter's moon Io and compare results of our study with what is reported in the literature. We used our published observations and supplemented them with new measurements carried out with the polarimeters mounted on the 2.6 m Shajn telescope of the Crimean Astrophysical Observatory and the 2 m telescope of the Peak Terskol Observatory in the UBVRI bands at phase angles between 10° and 12° in August 2023 – February 2024. We have determined that amplitude of the orbital polarization in the V band does not exceed ≈0.1 %. It is the deepest −0.17 ± 0.03 % at L ≈ 270° and the shallowest −0.07 ± 0.03 % near L ≈ 130°. These parameters differ markedly from that obtained by Zellner and Gradie (1975), which found that the orbital polarization variations from 0.4 to 0.5 % for α > 10°, and the negative branch is the deepest near L = 160° and the shallowest near L = 300°. These differences may be a consequence of changes in the reflective properties of the local areas of Io's surface due to long-term changes in Io's local or global volcanic activity.

这项工作的目的是研究木星卫星木卫一偏振的经度（轨道）依赖性，并将我们的研究结果与文献报道的结果进行比较。我们使用了已发表的观测数据，并在 2023 年 8 月至 2024 年 2 月期间使用克里米亚天体物理观测站 2.6 米 Shajn 望远镜和峰顶 Terskol 观测站 2 米望远镜在 UBVRI 波段的 10°至 12°相位角范围内进行了新的测量。我们确定 V 波段的轨道极化振幅不超过 ≈0.1%。在 L≈270° 时，偏振幅度最深-0.17 ± 0.03 %，在 L≈130° 附近，偏振幅度最浅-0.07 ± 0.03 %。这些参数与 Zellner 和 Gradie（1975 年）得到的参数有明显不同，后者发现在 α > 10° 时轨道极化变化从 0.4% 到 0.5%，负分支在 L = 160° 附近最深，在 L = 300° 附近最浅。这些差异可能是由于木卫二局部或全球火山活动的长期变化导致木卫二表面局部区域反射特性发生变化的结果。

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引用次数: 0

New astrometric positions for six Jovian irregular satellites using Gaia DR3 in 2016 — 2021 2016-2021年利用盖亚DR3对六颗木卫二不规则卫星进行新的天体测量定位

IF 2.5 2区物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS

Icarus

Pub Date : 2024-10-24 DOI: 10.1016/j.icarus.2024.116352

X. Lu , Q.Y. Peng , A. Vienne , X.Q. Fang , F.R. Lin

The Jovian system is like a miniature solar system, with the system being more than twice as massive as all the other planets combined and having many natural satellites. Its formation and early evolution had a profound influence on our knowledge of the sculpting of the architecture of the solar system. Astrometric observations are of importance, based on these observations, its orbital dynamics, as well as its origin sometimes, of a solar system object can be determined. We aimed to obtain good astrometric positions of some irregular satellites Elara, Pasiphae, Sinope, Lysithea, Carme and Ananke to refine their orbits and ephemerides, and to understand their dynamics. We have taken, processed and reduced 964 ground-based CCD frames obtained between 2016 and 2021 by the 2.4 m telescope at the Lijiang Station of Yunnan Observatory over 27 nights. Among CCD image processing, the image subtraction technique of ISIS is employed to eliminate star images that are close to or/and almost overlapped with those of our targets in 2019. The star catalog Gaia DR3 is utilized for astrometric calibration, in which a weight scheme is applied to solve more accurate plate model. For all targets, their theoretical positions are retrieved from the Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE) ephemeris. Our results show the mean (O - C)s (observed minus computed) of the positional residuals of all targets are

- 0^{''} . 007

and

0^{''} . 011

in R.A. and Dec., respectively. Their corresponding standard deviations are about

0^{''} . 05

in each direction, except for Ananke (the faintest satellite) with its standard deviation about

0^{''} . 08

in each direction.

木卫三系统就像一个微型太阳系，其质量是所有其他行星质量总和的两倍多，并且拥有许多天然卫星。它的形成和早期演化对我们了解太阳系的结构雕刻有着深远的影响。天体测量观测非常重要，根据这些观测，可以确定太阳系天体的轨道动力学，有时还可以确定其起源。我们的目标是获得一些不规则卫星 Elara、Pasiphae、Sinope、Lysithea、Carme 和 Ananke 的良好天体测量位置，以完善它们的轨道和星历表，并了解它们的动态。我们利用云南天文台丽江站的 2.4 米望远镜，历经 27 个夜晚，拍摄、处理并缩减了 2016 年至 2021 年期间的 964 幅地面 CCD 图像。在 CCD 图像处理中，采用了 ISIS 的图像减法技术，以剔除与 2019 年目标图像接近或/和几乎重叠的恒星图像。星表 Gaia DR3 用于天体测量校准，其中采用了加权方案来求解更精确的板块模型。所有目标的理论位置都是从法国天体物理和计算研究所（IMCCE）的星历表中获取的。结果显示，所有目标的位置残差（观测值减去计算值）的平均值（O - C）分别为-0′′.007（R.A.）和0′′.011（Dec.）。除了 "阿南克"（最暗卫星）的标准偏差约为0′′.08之外，其他卫星的标准偏差均为0′′.05。

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引用次数: 0

NAROO program: Analysis of USNO Galilean observations 1967–1998 NAROO 计划：美国国家空间研究组织（USNO）1967-1998 年伽利略观测数据分析

IF 2.5 2区物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS

Icarus

Pub Date : 2024-10-22 DOI: 10.1016/j.icarus.2024.116344

V. Robert , D. Pascu , V. Lainey , J.-E. Arlot

The New Astrometric Reduction of Old Observations (NAROO) program is dedicated to the measurement of astrophotographic plates and the analysis of old observations for scientific purposes. One of the main objectives of the NAROO program is to provide accurate positional measurements of planets and satellites to improve our knowledge of their orbits and dynamics, and to infer the accuracy of the planet and satellite ephemerides. We digitized 553 astronegatives of the Galilean satellites taken with the McCormick 26-inch refractor in 1967/68 and the U.S. Naval Observatory 26-inch refractor from 1973 to 1998, resulting in 2650 individual observations. We measured and reduced these observations through an optimal process that includes image, instrumental, and spherical corrections using Gaia-DR3 catalog to provide the most accurate equatorial (RA, Dec) ICRS (Gaia-CRF3) positions. 4819 positions of the Galilean satellites have been determined with an accuracy of 55 mas (160 km at Jupiter), near the limit of the photographic technique for such work. These data can help to improve the equatorial positions of Jupiter. They also can be used in the context of quantifying tidal effects and will still be useful when Europa Clipper and Juice data will become available.

新天体测量旧观测数据还原（NAROO）计划致力于为科学目的测量天体摄影板和分析旧观测数据。NAROO 计划的主要目标之一是提供行星和卫星的精确位置测量数据，以增进我们对其轨道和动力学的了解，并推断行星和卫星星历表的准确性。我们对 1967/68 年用麦考密克 26 英寸折射镜和 1973 年至 1998 年用美国海军天文台 26 英寸折射镜拍摄的 553 幅伽利略卫星天文照片进行了数字化处理，得到了 2650 个单独的观测数据。我们利用 Gaia-DR3 星表对这些观测数据进行了测量和缩减，其中包括图像、仪器和球面校正，以提供最精确的赤道（RA，Dec）ICRS（Gaia-CRF3）位置。伽利略卫星的 4819 个位置已经确定，精度为 55mas（木星 160 公里），接近此类工作的摄影技术极限。这些数据有助于改进木星的赤道位置。这些数据还可用于对潮汐效应进行量化，在获得 Europa Clipper 和 Juice 数据后仍将有用。

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引用次数: 0

Expected constraints on Phobos interior from the MMX gravity and rotation observations MMX重力和自转观测对火卫一内部的预期约束

IF 2.5 2区物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS

Icarus

Pub Date : 2024-10-21 DOI: 10.1016/j.icarus.2024.116343

Alfonso Caldiero, Sébastien Le Maistre

The origin of the Martian moons is still uncertain, and knowledge about their interior could provide support to some of its leading theories. In preparation for the JAXA Martian Moons eXploration (MMX) mission, we review our current knowledge on the interior of Phobos, and provide synthetic tests showing how the gravity and rotation determination could allow the detection of specific interior-structure properties. The inversion of the geodetic observables for the retrieval of the internal mass distribution of a set of synthetic interior models is performed via non-linear least-squares, where the interior parameterization is based on the level-set method. We additionally provide simple expressions allowing to relate some of these interior models to the geodetic observables of Phobos. The results, based on realistic measurement resolution and noise scenarios, show good retrievals for most of the models at the data resolutions expected from MMX. Specifically, we find the gravity information is realistically sufficient for the detection of mass anomalies below the Stickney crater, as well as large scale heterogeneous regions within plausible rubble-pile structures. Libration helps retrieve the more degenerate models for gravity, such as those with concentric layers or with density varying linearly with depth. The incremental improvement from further adding a hypothetical mean obliquity measurement is marginal. Finally, we apply the level-set inversion and the analytical formulas to estimate possible interior characteristics of the ‘real’ Phobos from the currently-available scarce geodetic observables. The level-set solutions for the real-data inversion generally converge to a higher mass concentration towards the surface in the equatorial region. Markov chain Monte Carlo estimations of parameters relative to a simple 2-layer model or a radial density distribution similarly hint at a lighter region inside of Phobos.

火星卫星的起源仍不确定，对其内部的了解可以为一些主要理论提供支持。在为日本宇宙航空研究开发机构（JAXA）的火星卫星探索（MMX）任务做准备的过程中，我们回顾了我们目前对火卫一内部的了解，并提供了合成测试，显示重力和自转测定如何能够探测到特定的内部结构特性。通过非线性最小二乘法对大地测量观测数据进行反演，以检索一组合成内部模型的内部质量分布，其中内部参数化基于水平集方法。此外，我们还提供了简单的表达式，可以将其中一些内部模型与火卫一的大地测量观测数据联系起来。根据现实的测量分辨率和噪声情况得出的结果表明，在 MMX 预期的数据分辨率下，大多数模型的检索结果都很好。具体来说，我们发现重力信息足以探测到斯蒂克尼陨石坑下方的质量异常，以及可信碎石堆结构内的大尺度异质区域。重力校准有助于检索更为退化的重力模型，例如具有同心层或密度随深度线性变化的模型。进一步增加假定的平均倾角测量所带来的增量改进微乎其微。最后，我们应用水平集反演和分析公式，根据目前可用的稀缺大地测量观测数据来估计 "真实 "火卫一可能的内部特征。真实数据反演的水平集解一般都趋向于赤道区域向地表的较高质量浓度。马尔科夫链蒙特卡洛参数估计与简单的两层模型或径向密度分布相比较，同样暗示火卫一内部有一个较轻的区域。

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引用次数: 0

Ab initio strewn field for small asteroids impacts 小行星撞击的 Ab initio 散射场

IF 2.5 2区物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS

Icarus

Pub Date : 2024-10-21 DOI: 10.1016/j.icarus.2024.116345

Albino Carbognani , Marco Fenucci , Raffaele Salerno , Marco Micheli

In recent years, nine small near-Earth asteroids were discovered a few hours before the collision with the Earth: these are about one metre in diameter objects that have all disintegrated in the atmosphere, generating bright fireballs without causing damage. In some cases, several meteorites have been recovered. In cases like these, it is not always possible to triangulate the fireball generated by the asteroid’s fall to circumscribe the strewn field position. For this reason, it can be important to compute a strewn field “ab initio”, i.e. propagating the asteroid’s trajectory in the atmosphere starting from the initial conditions obtained directly from the heliocentric orbit, coupled with some reasonable hypothesis about the mean strength and the mass of the fragments to “sample” the strewn field. By adopting a simple fragmentation model coupled with a real atmospheric profile, useful results can be obtained to locate the strewn field, as we will show for the recent falls of asteroids 2024 BX1, 2023 CX1 and 2008 TC3. It was possible to locate the strewn field of our study cases with an uncertainty of the order of one kilometre with the mean strength in the range 0.5–5 MPa and the mass of the possible final fragments in the 1 g–1 kg range. We have also verified that a pancake phase after fragmentation is unnecessary to locate the strewn field for a small asteroid fall.

近年来，在与地球相撞前几小时发现了九颗小型近地小行星：这些小行星直径约一米，全部在大气层中解体，产生明亮的火球，但没有造成损害。在某些情况下，还找到了几块陨石。在这种情况下，并不总是能够对小行星坠落产生的火球进行三角测量，以确定散落的位置。因此，必须 "从头开始 "计算条裂场，即从直接从日心轨道获得的初始条件开始，在大气层中传播小行星的轨迹，再加上一些关于平均强度和碎片质量的合理假设，对条裂场进行 "取样"。通过采用一个简单的碎裂模型和一个真实的大气剖面，可以获得有用的结果来确定条纹场的位置，正如我们将展示的最近坠落的小行星 2024 BX1、2023 CX1 和 2008 TC3 的情况。在平均强度为 0.5-5 兆帕，最终碎片的质量为 1 克-1 千克的情况下，我们可以在不确定度为一千米的范围内确定我们研究案例中的条状磁场的位置。我们还验证了在小行星坠落过程中，碎裂后的饼状阶段不需要对条状磁场进行定位。

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引用次数: 0

Rare earth element assessment in Jezero crater using the Planetary Instrument for X-ray Lithochemistry on the Mars 2020 rover Perseverance: A case study of cerium 利用 "毅力 "号火星探测器上的 X 射线岩石化学行星仪器对杰泽罗陨石坑进行稀土元素评估：铈的案例研究

IF 2.5 2区物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS

Icarus

Pub Date : 2024-10-21 DOI: 10.1016/j.icarus.2024.116355

S.J. VanBommel , S. Sharma , T.V. Kizovski , C.M. Heirwegh , J.R. Christian , A.L. Knight , B. Ganly , A.C. Allwood , J.A. Hurowitz , M.M. Tice , M.L. Cable , W.T. Elam , M.W.M. Jones , B.C. Clark , A.H. Treiman , M.E. Schmidt , Y. Liu , A. Das

The “Planetary Instrument for X-ray Lithochemistry” (PIXL) X-ray spectrometer conducts in situ geochemical analyses of martian rocks and regolith interrogated by the Mars 2020 rover, Perseverance. In addition to quantifying primary rock-forming elements, PIXL can quantify trace elements that in turn can provide additional constraints on the geologic history of Mars. Accurate quantifications of trace elements can require additional analytical techniques to mitigate experimental, background, and crystalline effects within PIXL spectra. In this study, we focus on reducing the impact of these effects and investigate the potential presence of rare earth elements (REEs). The study specifically investigates cerium given its typical relative abundance in many geologic materials compared to other REEs and its potential to mimic fluorescence features produced by organics under deep UV excitation. A detailed analysis of PIXL targets analyzed through the first 887 martian days of the Perseverance mission did not produce any conclusive Ce detections. Phosphorus-enriched materials analyzed by PIXL are estimated to contain sub-675 ppm Ce and sulfate-enriched materials sub-450 ppm Ce. The method presented can help constrain limits on the abundance of additional trace elements of interest that also face a similar analytical burden. PIXL's potential to assess REE abundances, outside of yttrium, is limited for expected concentrations in surface materials. Determining most REE concentrations in materials interrogated by Perseverance will therefore likely require terrestrial analyses.

X 射线岩石化学行星仪器"（PIXL）X 射线光谱仪对火星 2020 年探测器 "毅力号 "探测到的火星岩石和碎屑进行原位地球化学分析。除了对主要成岩元素进行量化外，PIXL 还能对痕量元素进行量化，而痕量元素反过来又能为火星地质历史提供额外的制约因素。痕量元素的精确定量需要额外的分析技术，以减轻 PIXL 光谱中的实验、背景和晶体效应。在本研究中，我们将重点放在减少这些效应的影响上，并调查稀土元素 (REE) 的潜在存在。与其他稀土元素相比，铈在许多地质材料中具有典型的相对丰度，而且在深紫外激发下有可能模仿有机物产生的荧光特征，因此本研究特别对铈进行了调查。在毅力号任务的前 887 个火星日中，对 PIXL 目标进行了详细分析，但没有发现任何确凿的铈探测结果。据估计，PIXL 分析的富磷材料中的 Ce 含量低于 675 ppm，富硫酸盐材料中的 Ce 含量低于 450 ppm。所介绍的方法有助于限制其他相关痕量元素的丰度，这些元素也面临着类似的分析负担。除钇之外，PIXL 评估 REE 丰度的潜力对于地表材料中的预期浓度是有限的。因此，要确定 Perseverance 所研究材料中的大多数 REE 浓度，可能需要进行地面分析。

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引用次数: 0

Density of Uranus moons: Evidence for ice/rock fractionation during planetary accretion 天王星卫星的密度：行星吸积过程中冰/岩石分馏的证据

IF 2.5 2区物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS

Icarus

Pub Date : 2024-10-20 DOI: 10.1016/j.icarus.2024.116354

Bruno Reynard , Christophe Sotin

Current models suggest the five regular moons of Uranus formed in a single stage from a primary planetary disk or a secondary impact disk. Using latest estimates of moon masses (Jacobson, 2014), we find a power-law relationship between size and density of the moons due to varying rock/ice ratios caused by fractionation processes. This relationship is better explained by mild enrichment of rock with respect to ice in the solids that aggregate to form the moons following Rayleigh law for distillation (Rayleigh, 1896) than by differential diffusion in the disk, although the two mechanisms are not exclusive. Rayleigh fractionation requires that moon composition and density reflect their order of formation in a closed-system circumplanetary disk. For Uranus, the largest and densest moons Titania and Oberon (R ∼ 788 and 761 km, respectively) first formed, then the mid-sized Umbriel and Ariel (585 and 579 km), satellites in each pair forming simultaneously with similar composition, and finally the small rock-depleted Miranda (236 km). Fractionation likely occurred through impact vaporization during planetesimal accretion. This mechanism would add to those affecting the composition of accreting planets and moons in disks such as temporal/spatial variation of disk composition due to temperature gradients, advection, and large impacts. In the outer solar nebula, Rayleigh fractionation may account for the separation of a rock-dominated reservoir, and an ice-dominated reservoir, currently represented by CI carbonaceous chondrite/type-C asteroids and comets, respectively. Potential consequences for Uranus moons' composition are discussed.

目前的模型表明，天王星的五颗规则卫星是在一个单一阶段从主行星盘或次级撞击盘中形成的。利用对卫星质量的最新估算（雅各布森，2014 年），我们发现卫星的大小和密度之间存在幂律关系，这是由于分馏过程导致的岩石/冰比率的变化造成的。根据瑞利蒸馏定律（Rayleigh，1896 年），在聚合形成卫星的固体中，岩石相对于冰有轻度富集，这比圆盘中的差分扩散更能解释这种关系，尽管这两种机制并不排斥。雷利分馏法要求卫星的成分和密度反映其在封闭系统环行星盘中的形成顺序。对于天王星来说，最大和密度最大的卫星泰坦尼娅和奥伯龙（R ∼ 788 和 761 千米）首先形成，然后是中等大小的翁布里亚尔和阿里尔（585 和 579 千米），每对卫星同时形成，成分相似，最后是小的贫岩米兰达（236 千米）。分馏很可能是在行星吸积过程中通过撞击汽化发生的。这一机制将补充那些影响磁盘中吸积行星和卫星成分的机制，如温度梯度、平流和大型撞击导致的磁盘成分的时间/空间变化。在外层太阳星云中，瑞利分馏可能是目前分别由CI碳质软玉/C型小行星和彗星代表的以岩石为主的储层和以冰为主的储层分离的原因。讨论了天王星卫星组成的潜在后果。

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