Three-Dimensional Structure of Hayabusa Samples: Origin and Evolution of Itokawa Regolith
A. TsuchiyamaMasayuki UesugiTakashi MatsushimaTatsuhiro MichikamiT. KadonoTomoki NakamuraKentaro UesugiTsukasa NakanoScott A. SandfordRyo NoguchiToru MatsumotoJunya MatsunoTakashi NaganoYuta ImaiAkihisa TakeuchiYoshio SuzukiT. OgamiJun KatagiriM. EbiharaT. R. IrelandF. KitajimaKeisuke NagaoHiroshi NaraokaT. NoguchiRyuji OkazakiHisayoshi YurimotoM. E. ZolenskyToshifumi MukaiMasanao AbeToru YadaAkio FujimuraMakoto YoshikawaJun’ichiro Kawaguchi
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Laboratory analysis of samples returned from an asteroid establishes a direct link between asteroids and meteorites and provides clues to the complex history of the asteroid and its surface.Keywords:
Regolith
Particle (ecology)
Early descriptions of regoliths on small bodies were devised to account for observations of asteroids (Chapman 1971, 1976) and the gas-rich meteorites (Anders 1975). Lack of agreement between these approaches prompted Housen et al. (1978, 1979) to examine the problem in detail. The resulting model predicted that moderate-sized (100-300 km) asteroids should evolve regoliths up to a few kilometers deep which could be source regions of gas-rich meteorites. Smaller objects should have regoliths ranging from dust coatings to meters-thick layers depending on the strength of the object. The earlier model could not treat asteroids larger than 300 km in diameter. The model, now modified to treat larger-sized objects, predicts regolith depths, on asteroids larger than 300 km, which decrease with increasing size. A regolith depth of 7 m is predicted for the lunar maria in reasonable agreement with the observed depths of 5 m.
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Asteroid belt
Near-Earth object
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Abstract We propose that the Taurid meteor shower may contain bodies able to survive and be recovered as meteorites. We review the expected properties of meteorite‐producing fireballs, and suggest that end heights below 35 km and terminal speeds below 10 km s −1 are necessary conditions for fireballs expected to produce meteorites. Applying the meteoroid strength index ( PE criteria) of Ceplecha and McCrosky (1976) to a suite of 33 photographically recorded Taurid fireballs, we find a large spread in the apparent meteoroid strengths within the stream, including some very strong meteoroids. We also examine in detail the flight behavior of a Taurid fireball ( SOMN 101031) and show that it has the potential to be a (small) meteorite‐producing event. Similarly, photographic observations of a bright, potential Taurid fireball recorded in November of 1995 in Spain show that it also had meteorite‐producing characteristics, despite a very high entry velocity (33 km s −1 ). Finally, we note that the recent Maribo meteorite fall may have had a very high entry velocity (28 km s −1 ), further suggesting that survival of meteorites at Taurid‐like velocities is possible. Application of a numerical entry model also shows plausible survival of meteorites at Taurid‐like velocities, provided the initial meteoroids are fairly strong and large, both of which are characteristics found in the Taurid stream.
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На основании анализа более 500 орбит метеороидных и болидных роев по опубликованным каталогам нами была установлена связь метеорита Križevci, порожденного болидом 4 февраля 2011 г. над Хорватией [1] с метеороидным роем Канкрид (No. 166 (а), [2, 3]). Известный критерий Саутворта-Хокинса дает величину D SH = 0.128, которая является вполне приемлемой для достаточно хорошего согласия орбит метеорита и роя. Динамический параметр Тиссерана указывает на астероидное происхождение роя и метеорита. Таким образом, выявлен еще один метеоритообразующий рой, который дополняет список 14 метеоритообразующих роев, найденных нами ранее [4]. Эти рои имеют важное значение с точки зрения потенциальной опасности при встрече их с Землей. В работе приводится краткая информация о таком редком явлении, которое названо А. Брезиной [5] «цепным падением» метеоритов. Based on the analysis of more than 500 orbits of meteoroid and reball streams according to published catalogs, we established the connection of the Križevci meteorite generated by the bolide on February 4, 2011 over Croatia [1] with a meteoroid stream Cancrid (No. 166 (a), [2, 3]). The well-known Southworth-Hawkins criterion gives a value of D SH = 0.128, which is quite acceptable for a fairly good agreement of the orbits of the meteorite and the stream. The dynamic parameter of Tisserand indicates the asteroid origin of the stream and the meteorite. Thus, this is yet another meteorite-forming stream that complements the list of 14 meteorite-forming streams that we found earlier [4]. These streams have an signi cance in terms of potential danger when they approach the Earth. The paper provides brief information about such a rare phenomenon, which is called the “chain fall” of meteorites by A. Brezina [5].
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Asteroid belt
Parent body
Allende meteorite
Near-Earth object
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Most meteorite researchers are confident that the near-Earth asteroids are the immediate parent bodies of the chondritic meteorites. Asteroid astronomers generally accept that most of the near-Earth asteroids originate in the Main Asteroid Belt, although some, probably around 10% (estimates have ranged as high as 50% in the past) are inert residues of comet nuclei (Wetherill and Chapman, 1988). However, when it comes to more precise links between asteroids and meteorites there are problems. As discussed below, the spectra do not fit; the commonest kinds of meteorites have spectra that match very few asteroids, while the majority of asteroids have spectra that match very few meteorites. Either the asteroids are camoflaging themselves or most of the meteorites are coming from very few sources. Just to compound the mystery, Eros, which has many of the compositional properties of an LL chondrite, has significant differences. We shall return to this below.
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Regolith from C (and related) asteroid bodies are a focus of the current missions Dawn at Ceres, Hayabusa 2 and OSIRIS REx. An asteroid as large as Ceres is expected to be covered by a mature regolith, and as Hayabusa demonstrated, flat and therefore engineeringly-safe ponded deposits will probably be the sampling sites for both Hayabusa 2 and OSIRIS REx. Here we examine what we have learned about the mineralogy of fine-grained asteroid regolith from recent meteorite studies and the examination of the samples harvested from asteroid Itokawa by Hayabusa.
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Abstract In recent years, numerous meteorites have been collected in desert areas in northern and western China. We describe the environment of some deserts in this region, and the petrological and mineralogical characteristics of 49 of the recovered ordinary chondrites. They consist of 14 H chondrites, 33 L chondrites, and 2 LL chondrites. Of the 300 desert meteorites with approved names from deserts in China, there have been 287 ordinary chondrites, six iron meteorites, one CO3 chondrite, one diogenite, one ureilite, one brachinite, one eucrite, and one EL7 chondrite. Forty‐two dense meteorite collection areas (DCAs) have been defined, mainly located in northern and western China. The meteorites collected are mainly from the Kumtag DCA, followed by the Alatage Mountain, Loulan Yizhi, Hami, and Lop Nur DCAs. After tentative pairing of the meteorites, we estimate that the ordinary chondrites account for 72% of the desert meteorites collected in China, with 63 H chondrites, 133 L chondrites, and 20 LL chondrites. This dominance of L chondrites contrasts with other deserts, which may result from the insufficient collection or bias in pairing of ordinary chondrites. The mass distribution of meteorites from different DCAs in China is consistent with that from DCAs in Africa. Based on the available information and the meteorite flux model proposed by previous studies, we suggest that the time over which meteorites have been accumulated in the southern Hami DCA might be >10 kyr. Therefore, the southern Hami region is currently the most suitable area for meteorite collection in China.
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Abstract Space-based and remote sensing observations reveal that regolith – a layer of loose unconsolidated material – is present on all asteroids, including very small, subkm-sized near- Earth asteroids (NEAs) such as (25143) Itokawa. Classically, regolith is believed to be produced by the ejecta of impact craters produced by small particles hitting asteroid surfaces. Such an explanation works for bodies whose gravity field is strong enough for substantial reaccretion of impact debris, but it fails to account for the ubiquitous presence of regolith also on small asteroids with weaker gravity. Several works have proposed that the thermal fatigue due to a huge number of day/night temperature cycles is a process that contributes to the formation of regolith on the Moon, Mercury, and on the NEA (433) Eros by fracturing boulders and rocks on their surfaces. However, this process lacks a demonstration: in order to study under which conditions rock cracking on NEAs occurs, we calculated typical temperature cycles for NEAs and we performed laboratory experiments of similar thermal cycling on meteorites taken as analogue of asteroid surface material. We will present results of these experiments and discuss their implications regarding regolith formation on asteroids.
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Abstract Some of the fields of research that have captured the persistent interest of both scientists and the general public are meteor phenomena. The main goal in the study of meteoroid impacts into Earth’s atmosphere is the recovery of the remnant matter after the ablation in the form of meteorites. This is a complementary approach, yet cheap alternative, to a sample return mission. Meteoroids are messengers since the time of the formation of the solar system due to the fact that they have preserved the same composition. The study of meteorites provides information regarding the chemical composition from which the planets formed. The increasing number of all-sky camera networks in recent years has resulted in a large set of events available for study. Thus, it is very important to use a method that determines whether the meteoroid could produce a meteorite or not. In this paper we study the meteors detected by the FRIPON network in Romania with the use of all-sky cameras. We focus on the events with noticeable deceleration ( V f / V 0 < 0.8). We determine the ballistic coefficient α and the mass-loss parameter β for the selected sample. Based on this analysis the events are classified in three categories: (1) meteoroids that are likely to produce meteorites; (2) meteoroids that can possibly produce meteorites; (3) meteoroids that are unlikely to produce meteorites. The entry and final mass are determined for each event. From the recorded fireballs, we identified one possible meteorite dropper, and we analyzed its dynamical evolution.
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