Cosmic-ray exposure age accumulated in near-Earth space: A carbonaceous chondrite case study

IF 2.2 4区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Patrick M. Shober, Marc W. Caffee, Phil A. Bland
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Abstract

This study investigates the expected cosmic-ray exposure (CRE) of meteorites if they were to be ejected by a near-Earth object, that is, from an object already transferred to an Earth-crossing orbit by an orbital resonance. Specifically, we examine the CRE ages of CI and CM carbonaceous chondrites (CCs), which have some of the shortest measured CRE ages of any meteorite type. A steady-state near-Earth carbonaceous meteoroid probability density function is estimated based on the low-albedo near-Earth asteroid population, including parameters such as the near-Earth dynamic lifetime, the impact probability with the Earth, and the orbital parameters. This model was then compared to the orbits and CRE ages of the five CC falls with precisely measured orbits: Tagish Lake, Maribo, Sutter's Mill, Flensburg, and Winchcombe. The study examined two meteoroid ejection scenarios for CI/CM meteoroids: Main Belt collisions and ejections in near-Earth space. The results indicated that applying a maximum physical lifetime in near-Earth space of 2–10 Myr to meteoroids and eliminating events evolving onto orbits entirely detached from the Main Belt (Q < 1.78 au) significantly improved the agreement with the observed orbits of carbonaceous falls. Additionally, the CRE ages of three of the five carbonaceous falls have measured CRE ages one to three orders of magnitude shorter than expected for an object originating from the Main Belt with the corresponding semi-major axis value. This discrepancy between the expected CRE ages from the model and the measured ages of three of the carbonaceous falls indicates that some CI/CM meteoroids are being ejected in near-Earth space. This study proposes a nuanced hypothesis involving meteoroid impacts and tidal disruptions as significant contributors to the ejection and subsequent CRE age accumulation of CI/CM chondrites in near-Earth space.

近地空间积累的宇宙射线暴露年龄:碳质软玉案例研究
本研究调查了如果陨石被近地天体(即已经通过轨道共振转移到地球穿越轨道上的天体)抛射出来时,陨石的预期宇宙射线暴露(CRE)。具体来说,我们研究了 CI 和 CM 碳质球粒陨石(CCs)的 CRE 年龄,在所有陨石类型中,CI 和 CM 碳质球粒陨石的实测 CRE 年龄是最短的。根据低地温近地小行星群,包括近地动态寿命、撞击地球概率和轨道参数等参数,估算了稳态近地碳质陨石概率密度函数。然后将这一模型与精确测量轨道的五颗CC坠落的轨道和CRE年龄进行比较:塔吉什湖、马里博、萨特磨坊、弗伦斯堡和温奇科姆。该研究考察了 CI/CM 流星体的两种流星体抛射情况:主带碰撞和近地空间抛射。结果表明,将流星体在近地空间的最大物理寿命定为 2-10 Myr,并剔除完全脱离主带(Q < 1.78 au)的轨道演化事件,大大提高了与碳质坠落观测轨道的一致性。此外,在五颗碳质坠落物中,有三颗测得的碳质坠落物的 CRE 年龄比预期的要短一到三个数量级。模型的预期 CRE 年龄与三个碳质坠落的测量年龄之间的这种差异表明,一些 CI/CM 流星体正在近地空间喷射。本研究提出了一个微妙的假说,即流星体撞击和潮汐扰动是导致近地空间 CI/CM 星体抛射和随后 CRE 年龄累积的重要因素。
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来源期刊
Meteoritics & Planetary Science
Meteoritics & Planetary Science 地学天文-地球化学与地球物理
CiteScore
3.90
自引率
31.80%
发文量
121
审稿时长
3 months
期刊介绍: First issued in 1953, the journal publishes research articles describing the latest results of new studies, invited reviews of major topics in planetary science, editorials on issues of current interest in the field, and book reviews. The publications are original, not considered for publication elsewhere, and undergo peer-review. The topics include the origin and history of the solar system, planets and natural satellites, interplanetary dust and interstellar medium, lunar samples, meteors, and meteorites, asteroids, comets, craters, and tektites. Our authors and editors are professional scientists representing numerous disciplines, including astronomy, astrophysics, physics, geophysics, chemistry, isotope geochemistry, mineralogy, earth science, geology, and biology. MAPS has subscribers in over 40 countries. Fifty percent of MAPS'' readers are based outside the USA. The journal is available in hard copy and online.
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