Some consequences of meteoroid impacts on Saturn's rings
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Rings of Saturn
Regolith
1. Introduction Iwan Williams and Edmond Murad 2. The evolution of meteoroid streams Iwan Williams 3. Space dust measurements Eberhard Grun, Valeri Dikarev, Harald Kruger and Markus Landgraf 4. Extraterrestrial dust in the near-Earth environment George Flynn 5. Detection and analysis procedures for visual photographic and image intensified CCD meteor observations Robert Hawkes 6. Radar observations W. Jack Baggaley 7. Meteor trails as observed by Lidar Ulf von Zahn, J. Hoffner and William McNeil 8. In situ measurements of meteoritic ions Joseph Grebowsky and Arthur Aikin 9. Collected extraterrestrial materials: interplanetary dust particles, micrometeorites, meteorites, and meteoritic dust Frans Rietmeijer 10. Meteoroid impacts on spacecraft Luigi Foschini 11. Models of meteoritic metals in the atmosphere William McNeil, Edmond Murad and John Plane 12. Laboratory studies of meteoritic metal chemistry John Plane 13. Summary and future outlook Edmond Murad and Iwan Williams.
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Context. Cometary meteoroid trails exist in the vicinity of comets, forming a fine structure of the interplanetary dust cloud. The trails consist predominantly of the largest cometary particles (with sizes of approximately 0.1 mm–1 cm), which are ejected at low speeds and remain very close to the comet orbit for several revolutions around the Sun. In the 1970s, two Helios spacecraft were launched towards the inner Solar System. The spacecraft were equipped with in situ dust sensors which measured the distribution of interplanetary dust in the inner Solar System for the first time. Recently, when re-analysing the Helios data, a clustering of seven impacts was found, detected by Helios in a very narrow region of space at a true anomaly angle of 135 ± 1°, which the authors considered as potential cometary trail particles. However, at the time, this hypothesis could not be studied further. Aims. We re-analyse these candidate cometary trail particles in the Helios dust data to investigate the possibility that some or all of them indeed originate from cometary trails and we constrain their source comets. Methods. The Interplanetary Meteoroid Environment for eXploration (IMEX) dust streams in space model is a new and recently published universal model for cometary meteoroid streams in the inner Solar System. We use IMEX to study the traverses of cometary trails made by Helios. Results. During ten revolutions around the Sun, the Helios spacecraft intersected 13 cometary trails. For the majority of these traverses the predicted dust fluxes are very low. In the narrow region of space where Helios detected the candidate dust particles, the spacecraft repeatedly traversed the trails of comets 45P/Honda-Mrkos-Pajdušáková and 72P/Denning-Fujikawa with relatively high predicted dust fluxes. The analysis of the detection times and particle impact directions shows that four detected particles are compatible with an origin from these two comets. By combining measurements and simulations we find a dust spatial density in these trails of approximately 10 −8 –10 −7 m −3 . Conclusions. The identification of potential cometary trail particles in the Helios data greatly benefited from the clustering of trail traverses in a rather narrow region of space. The in situ detection and analysis of meteoroid trail particles which can be traced back to their source bodies by spacecraft-based dust analysers provides a new opportunity for remote compositional analysis of comets and asteroids without the necessity to fly a spacecraft to or even land on those celestial bodies. This provides new science opportunities for future missions like DESTINY + (Demonstration and Experiment of Space Technology for INterplanetary voYage with Phaethon fLyby and dUst Science), Europa Clipper, and the Interstellar Mapping and Acceleration Probe.
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The regolith at the Apollo 16 landing site, the only Apollo landing site in the central lunar highlands, contains material derived from a number of sources. A model that accounts for the introduction of basin ejecta and mixing of the megaregolith is used to estimate the abundance of basin material in the Apollo 16 regolith. Megaregolith mixing model estimates of the abundance of primary ejecta from the Imbrium, Serenitatis, and Nectaris basins are found to be present in roughly equal (8–10%) proportions. Additionally, the presence of mare‐derived material in the Apollo 16 regolith suggests that a significant component of the regolith (15–23%) is derived from lateral transport. There are inherent difficulties in directly comparing model results with ground truth at Apollo 16. Results suggest shallower mixing during ejecta emplacement than predicted by Oberbeck et al. (1975).
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Zodiacal light
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Interplanetary particles larger than 10 −13 kg (3 µm) create significant light and ionization when colliding with the atmosphereof the Earth. Thisprovidesa way to study the higher mass component of the interplanetary dust complex, since the collecting area of the Earth’s atmosphere is large and the meteors resulting from these impacts are easily recordedwith optical cameras and radars. Particles in this size range have too low a flux relative to the size scale of in-situ dust detectors to be captured in dust detectors, and are difficult to detect remotely. Meteoroids are generally divided into two broad categories: shower meteors, which appearto come from narrowradiants as seenfromthesurfaceoftheEarthandoccurovera limited range of the Earth’s orbit every year, and sporadic meteors, which are always active and come from diffuse radiants. Recent advances in observing technology, particularly in automated data analysis, have produced great advances in the understanding of meteoroid distribution at 1 AU.
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ABSTRACT Impact ejecta production is a ubiquitous process that occurs on all airless bodies throughout the solar system. Unlike the Moon, which retains a large fraction of its ejecta, asteroids primarily shed their ejecta into the interplanetary dust population. These grains carry valuable information about the chemical compositions of their parent bodies that can be measured via in situ dust detection. Here, we use recent Lunar Atmosphere and Dust Environment Explorer /Lunar Dust Experiment measurements of the lunar dust cloud to calculate the dust ejecta distribution for any airless body near 1 au. We expect this dust distribution to be highly asymmetric, due to non-isotropic impacting fluxes. We predict that flybys near these asteroids would collect many times more dust impacts by transiting the apex side of the body compared to its anti-apex side. While these results are valid for bodies at 1 au, they can be used to qualitatively infer the ejecta environment for all solar-orbiting airless bodies.
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Evidence for the chemical composition of cometary meteoroids is available from the spectra of shower meteors, from the analysis of extra-terrestrial dust particles, from a study of residues in the bottom of microcraters on plates exposed to the interplanetary environment, and from measures of the relative abundances of non-atmospheric ions in the E-region of the earth’s upper atmosphere. Quantitative measures of chemical abundances in meteoroids, based on the four techniques listed, show that in general the cometary meteoroids encountered by the earth conform to the carbonaceous chondrites type 1 in the case of the commonest metallic elements. There is also qualitative evidence of the presence of significant quantities of some of the light volatiles.
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