Our work focuses on the spectrophotometric analysis of selected terrain and bright patches in the Khonsu region on the comet 67P/Churyumov-Gerasimenko. Despite the variety of geological features, ...their spectrophotometric properties appear to indicate a similar composition. It is noticeable that the smooth areas in Khonsu possess similar spectrophotometric behaviour to some other regions of the comet. We observed bright patches on Khonsu with an estimation of > 40% of normal albedo and suggest that they are associated to H2O ice. One of the studied bright patches has been observed to exist on the surface for more than 5 months without a major decay of its size, implying the existence of potential subsurface icy layers. Its location may be correlated with a cometary outburst during the perihelion passage of the comet in August 2015, and we interpret it to have triggered the surface modifications necessary to unearth the stratified icy layers beneath the surface. A boulder analysis on Khonsu leads to a power-law index of -3.1 +0.2/-0.3 suggesting a boulder formation, shaped by varying geological processes for different morphological units.
The 4th release of the SDSS Moving Object Catalog (SDSSMOC) is presently the largest photometric data-set of asteroids. Up to this point, the release of large asteroid data-sets has always been ...followed by a redefinition of asteroid taxonomy. In the years that followed the release of the first SDSSMOC, several classification schemes using its data were proposed, all using the taxonomic classes from previous taxonomies. The scope of the work is to propose a different interpretation scheme for gauging u'g'r'i'z' asteroid observations based on the continuity of spectral features. We analyzed the behavior of asteroid sampling through principal components analysis to understand the role of uncertainties in the SDSSMOC. We identified that asteroids in this space follow two separate linear trends using reflectances in the visible, which is characteristic of their spectrophotometric features. We have classified 69% of all SDSSMOC sample, which is a robustness higher than reached by previous SDSS classifications. Now, such behavior can be characterized by the variation of one single parameter, its position in the trend.
Between 2014 and 2016, ESA's Rosetta OSIRIS cameras acquired multiple-filters images of the layered nucleus of comet 67P/Churyumov-Gerasimenko, ranging from ultraviolet to near-infrared wavelengths. ...No correlation between layers disposition and surface spectral variegation has been observed so far. This paper investigates possible spectral differences among decametre-thickness outcropping layers of the biggest lobe of the comet by means of OSIRIS image dataset. A two-classes maximum likelihood classification was applied on consolidated outcrops and relative deposits identified on post-perihelion multispectral images of the big lobe. We distinguished multispectral data on the basis of the structural elevation of the onion-shell Ellipsoidal Model of 67P. The spatial distribution of the two classes displays a clear dependence on the structural elevation, with the innermost class resulting over 50 per cent brighter than the outermost one. Consolidated cometary materials located at different structural levels are characterized by different brightness and revealed due to the selective removal of large volumes. This variegation can be attributed to a different texture of the outcrop surface and/or to a different content of refractory materials.
Abstract
We provide a detailed geomorphological and spectrophotometric analysis of the circular niches located on the Seth region of 67P using OSIRIS images. The features can be related to landslide ...events that occurred on 67P and shaped its surface, as the recent Aswan cliff collapse detected in the same region. We therefore provide an analysis of the area pre- and post-perihelion suggesting that no specific changes have been observed. To assess this, after performing a geomorphological map of the area that allows us to identify different terrain units, we computed the boulders cumulative size frequency distribution (SFD) of the niches, before and after the perihelion passage. The niches SFDs are characterized by a similar trend with two different power-law indices within the same deposit: lower power-law value (between −2.3 and −2.7) for boulders smaller than 5 m and steeper power-law value (between −4.7 and −5.0) for boulders larger than 5 m. These trends suggest that smaller boulders have evolved and progressively have been depleted (lower power-law index), while bigger boulders are more representative of the event that generated the deposit and are less degraded. Then, we perform the spectrophotometric analysis of this region comparing pre- and post-perihelion results. We found colour changes within the area, in particular brighter patches related to the presence of exposed water ice mixed to the refractory materials have been detected in the post-perihelion images.
Context. To take advantage of the large dataset provided by the SDSS data, recently a new taxonomic scheme was proposed designed to be compatible with previous taxonomies. One interesting feature in ...this distribution is the large number of Qp asteroids scattered all around the main belt with a marked concentration in the Vesta region, where the Vp are found most frequently. Since the mineralogy and thermal evolution traditionally related to the classical Q- and V-type taxonomic classes (and by construction the Qp and Vp), this finding was quite surprising. Aims. We aim to observationally determine the mineralogy of a sample of Qp asteroids of and outside the Vesta family to test whether the Qp of the Vesta family are indeed basaltic, and whether the difference in band depth implied by the SDSS spectra relates to diffences in mineralogy with respect to the Vp. Moreover, we aim to determine whether the Qp outside Vesta family have an ordinary chondrite (OC) mineralogy and whether their spectra indeed correspond to Q-class asteroids. Methods. We observed a sample of asteroids classified as Qp-type in the literature, mainly located in the Vesta family and neighborhood, to confirm their mineralogy. Spectroscopic observations of 11 asteroids were obtained at the SOAR and IRTF telescopes in the visible and near-infrared region. Thermal observations of three objects were also carried out at the Gemini South telescope in order to determine the albedo of the asteroids. Results. The analysis indicated that all observed asteroids in the Vesta vicinity have a basalt-rich mineralogy, with no clear difference from other Vesta family members in terms of silicate composition. From our study it is not clear why these particular basaltic asteroids have a relatively suppressed band I so that they are classified as Qp. Two asteroids with an OC-compatible mineralogy were identified in the external part of the main belt, at around 2.8−2.9 AU. This discovery suggests new dynamical routes for the transport of Q-type asteroids to the near-Earth region and of OC meteorites to the Earth.
Abstract
The smallest member of the Didymos binary near-Earth object system (Dimorphos) is the target of the DART/LICIACube mission, the first attempt to change the orbit of another celestial body ...via a kinetic impactor. It is important to characterize the unperturbed system prior to the DART impact. In this work we obtained, for the first time, spectral characterization of the system at several rotational phases from TNG+DOLORES in the visible range (0.34–0.81
μ
m). This is crucial in order to disentangle the primary and secondary bodies and highlight eventual dishomogeneities on their surfaces. We confirm that a subtle but persistent spectral variability appears, even when compared with data obtained from previous 2003 and 2019 apparitions. While the reason for such variability is still under investigation, our analysis hints that different compositions could play a role. Future observations during the brighter 2022 apparition in synergy with data obtained from LUKE on board LICIACube will definitely tackle this conundrum.
To take advantage of the large data set provided by the SDSS data, recently a new taxonomic scheme was proposed designed to be compatible with previous taxonomies. Since the mineralogy and thermal ...evolution traditionally related to the classical Q- and V-type taxonomic classes, this finding was quite surprising. We aim to observationally determine the mineralogy of a sample of Qp asteroids of and outside the Vesta family to test whether the Qp of the Vesta family are indeed basaltic, and whether the difference in band depth implied by the SDSS spectra relates to diffences in mineralogy with respect to the Vp. The analysis indicated that all observed asteroids in the Vesta vicinity have a basalt-rich mineralogy, with no clear difference from other Vesta family members in terms of silicate composition. This discovery suggests new dynamical routes for the transport of Q-type asteroids to the near-Earth region and of OC meteorites to the Earth.
Living cells interact with their immediate environment by exerting mechanical forces, which regulate important cell functions. Elucidation of such force patterns yields deep insights into the physics ...of life. Here we present a top-down nanostructured, ultraflexible nanowire array biosensor capable of probing cell-induced forces. Its universal building block, an inverted conical semiconductor nanowire, greatly enhances both the functionality and the sensitivity of the device. In contrast to existing cellular force sensing architectures, microscopy is performed on the nanowire heads while cells deflecting the nanowires are confined within the array. This separation between the optical path and the cells under investigation excludes optical distortions caused by cell-induced refraction, which can give rise to feigned displacements on the 100 nm scale. The undistorted nanowire displacements are converted into cellular forces via the nanowire spring constant. The resulting distortion-free cellular force transducer realizes a high-resolution and label-free biosenor based on optical microscopy. Its performance is demonstrated in a proof-of-principle experiment with living Dictyostelium discoideum cells migrating through the nanowire array. Cell-induced forces are probed with a resolution of 50 piconewton, while the most flexible nanowires promise to enter the 100 femtonewton realm.
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