저작근 근전도에 관한 정상교합자와 ii급 부정교합자의 비교 연구

The composition of the primitive mantle derived here shows that Earth was assembled from material that shows many of the same chemical fractionation processes as chondritic meteorites. These processes occurred at the initial stage of the solar system formation, under conditions thought to be present in the solar nebula. But the stable isotope record excludes chondritic meteorites as the ‘building blocks’ of Earth. Meteorites formed in local environments separated from that part of the inner solar system where much of the material forming the terrestrial planets was sourced.

https://booksite.elsevier.com/brochures/treatiseongeochemistry/contents/sample2.pdf

Cosmochemical Estimates of Mantle Composition

During its approach to asteroid (101955) Bennu, NASA’s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft surveyed Bennu’s immediate environment, photometric properties, and rotation state. Discovery of a dusty environment, a natural satellite, or unexpected asteroid characteristics would have had consequences for the mission’s safety and observation strategy. Here we show that spacecraft observations during this period were highly sensitive to satellites (sub-meter scale) but reveal none, although later navigational images indicate that further investigation is needed. We constrain average dust production in September 2018 from Bennu’s surface to an upper limit of 150 g s–1 averaged over 34 min. Bennu’s disk-integrated photometric phase function validates measurements from the pre-encounter astronomical campaign. We demonstrate that Bennu’s rotation rate is accelerating continuously at 3.63 ± 0.52 × 10–6 degrees day–2, likely due to the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, with evolutionary implications.

/pdf/the-operational-environment-and-rotational-acceleration-of-25pb0r9b60.pdf

The operational environment and rotational acceleration of asteroid (101955) Bennu from OSIRIS-REx observations

Physics of shock waves and high-temperature hydrodynamic phenomena - Ya.B. Zeldovich and Yu.P. Raizer (translated from the Russian and then edited by Wallace D. Hayes and Ronald F. Probstein); Dover Publications, New York, 2002, 944 pp., $34.

The Wide-field Infrared Survey Explorer (WISE) has surveyed the entire sky at four infrared wavelengths with greatly improved sensitivity and spatial resolution compared to its predecessors, the Infrared Astronomical Satellite and the Cosmic Background Explorer. NASA's Planetary Science Division has funded an enhancement to the WISE data processing system called "NEOWISE" that allows detection and archiving of moving objects found in the WISE data. NEOWISE has mined the WISE images for a wide array of small bodies in our solar system, including near-Earth objects (NEOs), Main Belt asteroids, comets, Trojans, and Centaurs. By the end of survey operations in 2011 February, NEOWISE identified over 157,000 asteroids, including more than 500 NEOs and ~120 comets. The NEOWISE data set will enable a panoply of new scientific investigations.

https://iopscience.iop.org/article/10.1088/0004-637X/731/1/53/pdf

Preliminary results from neowise: an enhancement to the wide-field infrared survey explorer for solar system science

The Role of Target Properties and Projectile Velocity on Final Crater Morphology of Craters on Mercury

The First Detailed Look at Asteroid Ryugu with Visible Multi-band Camera on Hayabusa2

Introduction: Distinctive low-reflectance material (LRM) was first observed on Mercury in Mariner 10 flyby images [1]. Visible to near-infrared reflectance spectra of LRM are flatter than the average reflectance spectrum of Mercury, which is strongly red sloped (increasing in reflectance with wavelength). From Mariner 10 and early MErcury, Surface, Space, ENvironment, GEochemistry, and Ranging (MESSENGER) flyby observations, it was suggested that a higher content of ilmenite, ulvöspinel, carbon, or iron metal could cause both the characteristic dark, flat spectrum of LRM and the globally low reflectance of Mercury [1,2]. Once MESSENGER entered orbit, low Fe and Ti abundances measured by the X-Ray and Gamma-Ray Spectrometers ruled out ilmenite and ulvöspinel as important surface constituents [3,4] and implied that LRM was darkened by a different phase, such as carbon or small amounts of microor nanophase iron or iron sulfide dispersed in a silicate matrix. Low-altitude thermal neutron measurements of three LRM-rich regions confirmed an enhancement of 1–3 wt% carbon over the global abundance, supporting the hypothesis that the darkening agent in LRM is carbon [5]. Here, using the final calibration of the Mercury Dual Imaging System (MDIS) 8-color global mosaic, we examine the distribution and spectral properties of LRM on a global scale, and extrapolate the results of Peplowski et al. [5] to place bounds on the carbon abundance of different LRM deposits across Mercury. Distribution of Low Reflectance Material: LRM is distributed across Mercury, typically having been excavated from depth by craters and basins. In contrast to the brighter high reflectance plains (HRP) and smooth plains deposits, which exhibit morphological evidence of volcanism [e.g., 6-8], LRM is not associated with flow features or other evidence of a volcanic origin. Older LRM boundaries are generally diffuse, and grade into low-reflectance blue plains (LBP). Because of the common lack of sharp geologic boundaries, LRM has been defined primarily based on albedo and spectral shape, isolated through principal components (PC) analyses of MDIS color images [9]. LRM is the darkest material on Mercury, with an albedo of 4–5% at 560 nm (compared to a global 560-nm albedo of ~6%), and it exhibits a spectral slope that is substantially less red than the rest of Mercury. The low iron content of Mercury’s surface results in a lack of the spectral absorption bands typically used to map mafic minerals on planets and asteroids. Thus, mathematical transformations such as PC analysis are required to map subtle spectral differences. For example, the second principal component (PC2), captures a combination of spectral slope and curvature, isolating LRM and hollows as one endmember, with red material and HRP as the other end member. LBP and intermediate plains (IP) are transitional from LRM to HRP [10]. In [5], concentrated LRM exposures were defined as regions with a photometrically corrected reflectance of <5% (at 560 nm wavelength) and a PC2 value of <0.023. This value corresponds with the lower ~25% of the range of PC2 values for the whole planet. The resulting LRM map, overlain on the global color mosaic, is shown in Fig. 1a. There are some regional concentrations where many moderate sized craters or several larger basins excavated LRM in close proximity to one another. LRM is most immediately recognizable visually when excavated by craters and deposited onto high-reflectance red plains (HRP, as in Caloris basin), due to the contrasting reflectance and spectral slopes of the different stratigraphic layers. However, it is also abundant throughout the oldest, rough terrains, where its boundaries are more difficult to delineate as they grade into LBP. In these older terrains LRM is still apparently associated with crater ejecta, but the high density of craters excavating LRM results in a patchy distribution of low-reflectance, low-PC2 material.

Examining the Distribution and Concentration of Carbon on Mercury

242 formation of an impact crater will provide new constraints on the collisional evolution of the asteroid belt. To first order, higher strain rates yield smaller fragment sizes. As Fig. 1 shows, the relationship is really more complex. As a first step toward better understanding the failure of geological materials at fairly moderate strain rates— more akin to what a planetary body typically encounters during a planetary-scale impact—we embarked on an experimental investigation to probe the response of a model geological material (single-crystal quartz) under uniaxial compression. Dynamic compression experiments were conducted using a Kolsky bar, which allowed a detailed history of the stress–time response on the microsecond time scale to be obtained. Ultra-high-speed photography recorded the evolution of damage and the propagation of cracks. Experiments also were done at quasi-static loading rates to further determine the effect of loading rate. Again, images detailing the evolution of the failure process were recorded. An increase in compressive strength was observed with increased loading rate. In specimens that were not loaded to (catastrophic) failure, significant crack growth was observed during the mechanical unloading of the specimen. The mechanism (or mechanisms) responsible for generating and propagating these “unloading cracks” is currently under investigation. A parallel modeling effort is in progress (Fig. 2). Impacts initiate dynamic fracturing on macroand micro-scales, and the resulting fragmentation can be related to strain rate. Dynamic fracture has been directly observed at low strain rates (~10 −2 to 10−3 s−1, during earthquakes) and at high strain rates (~105 to 106 s−1, during laboratory-scale hypervelocity impact experiments). On the basis of firstorder estimates of the strain rate in the event (approximate impact velocity/projectile diameter) and numerical results such as those shown, the strain rates encountered in a typical planetary-scale impact range from ~100 to 102 s−1. These intermediate values lie within a strain rate regime that can be observed with the Kolsky bar, but are not easy to observe during typical small-scale hypervelocity (<2 km/s) impact experiments. Combining our numerical simulations with new dynamic fragmentation models derived from Kolsky bar experiments, we have begun to Figure 1. Factors that contribute to the failure of materials on the basis of classical dynamic fracture mechanics. Most of the region cratered by a bolide actually undergoes moderate rather than high strain rates, which result in different mechanical and failure behaviors of the impacted body. The Dynamic Fracture of Rocky Bodies: Applications to Planetary Impact Problems

Carolyn M. Ernst

Papers

The Role of Target Properties and Projectile Velocity on Final Crater Morphology of Craters on Mercury

The First Detailed Look at Asteroid Ryugu with Visible Multi-band Camera on Hayabusa2

Examining the Distribution and Concentration of Carbon on Mercury

The Dynamic Fracture of Rocky Bodies: Applications to Planetary Impact Problems

Crater formation in pre-existing target structures: Implications for small bodies