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Detailed images of highly porous small bodies show variety of the surface. One of the interesting findings is that the depressions on comets look shallower than the simple craters such as on the moon, that is the depth-to-diameter ratio of the depressions is smaller than ∼0.2. Although the mechanisms for the formation of the depression are controversial; such as collapse after the sublimation of the...
New tables to observe the planet Venus are presented with detailed information about the main spectral regions from 100nm to 1mm. The information hereby is updated thanks to the Venus Express legacy and recent ground-based observations, and we hope it can constitute a helpful tool for professional and amateur observers willing to support and coordinate with the JAXA's Venus Climate Orbiter/Akatsuki...
We have investigated the cloud top structure of Venus by analyzing ground-based images taken at the mid-infrared wavelengths of 8.66μm and 11.34μm. Venus at a solar phase angle of ∼90°, with the morning terminator in view, was observed by the Cooled Mid-Infrared Camera and Spectrometer (COMICS), mounted on the 8.2-m Subaru Telescope, during the period October 25–29, 2007. The disk-averaged brightness...
Iron meteorites and some M-class asteroids are generally understood to be fragments that were originally part of cores of differentiated planetesimals or part of local melt pools on primitive bodies. The parent bodies of iron meteorites may have formed in the terrestrial planet region, from which they were then scattered into the main belt (Bottke, W.F., Nesvorný, D., Grimm, R.E., Morbidelli, A.,...
We obtain an empirical relationship between porosity and the interparticle force of granular media based on measurement data on the ground. We apply the relationship to the condition of the surface of small bodies to estimate the porosity and the particle size of the regolith.
Chondrites are one of the major groups of meteorites. They consist of spherical objects called chondrules, which are typically (sub-)millimeter-sized, and fine-grained matrix between the chondrules. There exists a variety of models on the formation of chondrules, most of which have in common that chondrules were formed at some local place in the protoplanetary disk and later incorporated into the...
Ejecta patterns are experimentally examined around craters formed in a layer of glass beads by vertical impacts at low velocities. The diameters of the constituent glass beads of three different targets range 53–63μm, 90–106μm, and 355–500μm. The impact velocities and ambient pressures range from a few to 240ms −1 and from 500Pa to the atmospheric pressure, respectively. Various ejecta patterns...
Small primitive bodies were presumably highly porous when they formed and some still have low densities that are indicative of a high pore content. Therefore, after their formation, interplanetary dust impacting on their surface may have been captured because of their porous structure. The mechanism of dust penetration is thus of importance to understand the evolution of small bodies and the origin...
Previous laboratory impact experiments into sand and glass beads have enriched our understanding of the cratering process on granular media common on asteroids and planetary regolith. However, less attention has been paid to the fate of the projectile, such as its penetration depth in the granular medium, although this may be important for the regolith mixing process. We conducted laboratory experiments...
A large number of cometary dust particles were captured with low-density silica aerogels by NASA’s Stardust Mission. Knowledge of the details of the capture mechanism of hypervelocity particles in silica aerogel is needed in order to correctly derive the original particle features from impact tracks. However, the mechanism has not been fully understood yet. We shot hard spherical projectiles of several...
Porous internal structure is common among small bodies in the planetary systems and possible range of porosity, strength, and scale of in-homogeneity is wide. Icy agglomerates, such as icy dust aggregates in the proto-planetary disks or icy re-accumulated bodies of fragments from impact disruption beyond snow-line would have stronger bulk strength once the component particles physically connect each...
The Hayabusa Spacecraft Asteroid Multi-band Imaging Camera (AMICA) has acquired more than 1400 multispectral and high-resolution images of its target asteroid, 25143 Itokawa, since late August 2005. In this paper, we summarize the design and performance of AMICA. In addition, we describe the calibration methods, assumptions, and models, based on measurements. Major calibration steps include corrections...
Laboratory impact experiments have found that the shape of fragments over a broad size range is distributed around the mean value of the axial ratio 2:√2:1, which is independent of a wide range of experimental conditions. We report the shape statistics of boulders with size of 0.1–30m on the surface of Asteroid 25143 Itokawa based on high-resolution images obtained by the Hayabusa spacecraft in order...
We performed low-velocity impact experiments of gypsum spheres with porosity ranging from 0 to 61% and diameter ranging from 25 to 83 mm. The impact velocity was from 0.2 to 22 m/s. The target was an iron plate. The outcome of gypsum spheres with porosity 31–61% was different from those of non-porous ice [Higa M., Arakawa, M., Maeno, N., 1996. Planet. Space Sci. 44, 917–925; Higa M., Arakawa, M.,...
In this paper, we compare the outcome of high-velocity impact experiments on porous targets, composed of pumice, with the results of simulations by a 3D SPH hydrocode in which a porosity model has been implemented. The different populations of small bodies of our Solar System are believed to be composed, at least partially, of objects with a high degree of porosity. To describe the fragmentation of...
We determined the morphologies and dimensions of possible impact craters on the surface of Asteroid 25143 Itokawa from images taken by the Hayabusa spacecraft. Circular depressions, circular features with flat floors or convex floors, and circular features with smooth surfaces were identified as possible craters. The survey identified 38 candidates with widely varying morphologies including rough,...
The near-Earth Asteroid 25143 Itokawa, the target of the Japanese space mission Hayabusa, was observed in June, 2004 with the Torino photopolarimeter attached at the 2.15 m telescope of the El Leoncito Observatory (Argentina). The degree of linear polarization in five colors was measured over a wide range of phase angles, between 40° and 80°. The data obtained are sufficient to derive an estimate...
We performed laboratory experiments on the bidirectional reflectance of powdered surfaces of dunite, graphite, and Allende (CV3) and Gao (H5) meteorites. The particle size of each sample varied from tens to hundreds of micrometers. The absolute bidirectional reflectance was determined for two ranges of phase angle: from 2 o to 80 o at 0 o angle of incidence and from 2 o...
We performed new experiments with impacts on regolith-like layers of glass spheres to investigate the spatial and velocity distributions of ejecta with velocities higher than several hundred m sec −1 . Spherical nylon projectiles of 7.0 mm diameter were accelerated to about 4 km sec −1 using a two-stage light-gas gun. The ejecta were detected by thin Al foil targets of different thickness,...
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