Vesta's Shape and Morphology Jaumann, R.; Williams, D. A.; Buczkowski, D. L. ...
Science (American Association for the Advancement of Science),
05/2012, Letnik:
336, Številka:
6082
Journal Article
Recenzirano
Vesta's surface is characterized by abundant impact craters, some with preserved ejecta blankets, large troughs extending around the equatorial region, enigmatic dark material, and widespread mass ...wasting, but as yet an absence of volcanic features. Abundant steep slopes indicate that impact-generated surface regolith is underlain by bedrock. Dawn observations confirm the large impact basin (Rheasilvia) at Vesta's south pole and reveal evidence for an earlier, underlying large basin (Veneneia). Vesta's geology displays morphological features characteristic of the Moon and terrestrial planets as well as those of other asteroids, underscoring Vesta's unique role as a transitional solar system body.
The structure of the upper layer of a comet is a product of its surface activity. The Rosetta Lander Imaging System (ROLIS) on board Philae acquired close-range images of the Agilkia site during its ...descent onto comet 67P/Churyumov-Gerasimenko. These images reveal a photometrically uniform surface covered by regolith composed of debris and blocks ranging in size from centimeters to 5 meters. At the highest resolution of 1 centimeter per pixel, the surface appears granular, with no apparent deposits of unresolved sand-sized particles. The thickness of the regolith varies across the imaged field from 0 to 1 to 2 meters. The presence of aeolian-like features resembling wind tails hints at regolith mobilization and erosion processes. Modeling suggests that abrasion driven by airfall-induced particle "splashing" is responsible for the observed formations.
Images from the Mars Express HRSC (High-Resolution Stereo Camera) of debris aprons at the base of massifs in eastern Hellas reveal numerous concentrically ridged lobate and pitted features and ...related evidence of extremely ice-rich glacier-like viscous flow and sublimation. Together with new evidence for recent ice-rich rock glaciers at the base of the Olympus Mons scarp superposed on larger Late Amazonian debris-covered piedmont glaciers, we interpret these deposits as evidence for geologically recent and recurring glacial activity in tropical and mid-latitude regions of Mars during periods of increased spin-axis obliquity when polar ice was mobilized and redeposited in microenvironments at lower latitudes. The data indicate that abundant residual ice probably remains in these deposits and that these records of geologically recent climate changes are accessible to future automated and human surface exploration.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Visible, InfraRed, and Thermal Imaging Spectrometer (VIRTIS) on Rosetta obtained hyperspectral images, spectral reflectance maps, and temperature maps of the asteroid 21 Lutetia. No absorption ...features, of either silicates or hydrated minerals, have been detected across the observed area in the spectral range from 0.4 to 3.5 micrometers. The surface temperature reaches a maximum value of 245 kelvin and correlates well with topographic features. The thermal inertia is in the range from 20 to 30 joules meter⁻² kelvin⁻¹ second⁻⁰.⁵, comparable to a lunarlike powdery regolith. Spectral signatures of surface alteration, resulting from space weathering, seem to be missing. Lutetia is likely a remnant of the primordial planetesimal population, unaltered by differentiation processes and composed of chondritic materials of enstatitic or carbonaceous origin, dominated by iron-poor minerals that have not suffered aqueous alteration.
The Lake Chad basin, located in the centre of northern Africa, is characterized by strong climate seasonality with a pronounced short annual precipitation period and high potential ...evapotranspiration. Groundwater is an essential source for drinking-water supply, as well as for agriculture and groundwater-related ecosystems. Thus, assessment of groundwater recharge is very important although also difficult because of the strong effects of evaporation and transpiration, as well as the limited available data.
•System failures during maneuver coordination are evaluated.•The effect of an explanation of the system failure is investigated.•The results revealed decreased trust in the system after a failure for ...short time.•The explanations were perceived as helpful, but no effect on acceptance was found.
To support the coordination of road users in situations like merging or turning left, an advanced driver assistance system for cooperative driving could be helpful whether driving manually or automated. This simulator study investigated the behavior of drivers being confronted with system failures. In two test situations with system failures (loss of communication of the system and change of traffic environment), the system could not complete the coordination properly and the driver was informed about the system failure and the abortion of maneuver coordination. The focus of this study was to analyze the effect of system failures on drivers’ trust in the system and whether an explanatory message provided by the system would increase acceptance. Therefore, subjective data as well as gaze and physiological data of 32 participants were analyzed. The results revealed decreased trust in the system after experiencing a system failure, but no long term effect was found. The drivers evaluated the timing, as well as the content, of the explanatory message as appropriate. The explanations were perceived as helpful, but no effect on acceptance was found.
The High Resolution Stereo Camera (HRSC) of ESA׳s Mars Express is designed to map and investigate the topography of Mars. The camera, in particular its Super Resolution Channel (SRC), also obtains ...images of Phobos and Deimos on a regular basis. As HRSC is a push broom scanning instrument with nine CCD line detectors mounted in parallel, its unique feature is the ability to obtain along-track stereo images and four colors during a single orbital pass. The sub-pixel accuracy of 3D points derived from stereo analysis allows producing DTMs with grid size of up to 50m and height accuracy on the order of one image ground pixel and better, as well as corresponding orthoimages. Such data products have been produced systematically for approximately 40% of the surface of Mars so far, while global shape models and a near-global orthoimage mosaic could be produced for Phobos. HRSC is also unique because it bridges between laser altimetry and topography data derived from other stereo imaging instruments, and provides geodetic reference data and geological context to a variety of non-stereo datasets. This paper, in addition to an overview of the status and evolution of the experiment, provides a review of relevant methods applied for 3D reconstruction and mapping, and respective achievements. We will also review the methodology of specific approaches to science analysis based on joint analysis of DTM and orthoimage information, or benefitting from high accuracy of co-registration between multiple datasets, such as studies using multi-temporal or multi-angular observations, from the fields of geomorphology, structural geology, compositional mapping, and atmospheric science. Related exemplary results from analysis of HRSC data will be discussed. After 10 years of operation, HRSC covered about 70% of the surface by panchromatic images at 10–20m/pixel, and about 97% at better than 100m/pixel. As the areas with contiguous coverage by stereo data are increasingly abundant, we also present original data related to the analysis of image blocks and address methodology aspects of newly established procedures for the generation of multi-orbit DTMs and image mosaics. The current results suggest that multi-orbit DTMs with grid spacing of 50m can be feasible for large parts of the surface, as well as brightness-adjusted image mosaics with co-registration accuracy of adjacent strips on the order of one pixel, and at the highest image resolution available. These characteristics are demonstrated by regional multi-orbit data products covering the MC-11 (East) quadrangle of Mars, representing the first prototype of a new HRSC data product level.
•We present an overview of the main characteristics and operational achievements of HRSC after ten years in orbit.•Demonstrate significant improvements in HRSC data product accuracy based on in-flight data.•Present a new HRSC data product level based on integration of data from multiple orbits.•Review methods and exemplary results for mapping and science analysis, typically based on precise co-registration and joint analysis of DTMs and orthoimages.
•The effect of an HMI for cooperative driving on controllability is evaluated in a simulator study.•The study focuses on driver behavior in system limit and system failure situations.•The place (HUD ...vs. Cluster) and form (dynamic vs. static) of presentation are varied.•Analyzing subjective and objective parameters reveal that the most fitting HMI solution is a dynamic HUD.
Ambiguous situations in traffic often require communication and cooperation between road users. In order to resolve these situations and increase cooperative driving behavior in situations of merging or turning left, manual drivers could be assisted by an advanced driver assistance system (ADAS) for cooperative driving. This simulator study investigated the behavior of drivers confronted with system limits and failures of such a system. The ADAS used in this study informed the driver about an upcoming cooperation situation and gave advice on how to behave (e.g. reduce speed, change lane). Two test situations were implemented: a system freeze and an unexpected event, which could not be detected by the system. In order to find the most fitting HMI solution, the place of presentation (head-up display (HUD) vs. instrument cluster) as well as the form of presentation (dynamic vs. symbolic) were varied. The results indicated that the most fitting HMI solution to support the driver in a complex coordinated driving situation is a dynamic HUD, mainly due to the positive effect on glance behavior. However, advantages of both forms of presentation were revealed, as each form of presentation increased the probability of recognition for one of the test situations. The fewest collisions took place with the dynamic form of presentation.
ESA's Mars Express has successfully completed its nominal mission of one Martian year covering about 25% of the surface in stereo and color with resolutions up to 10
m/pixel by its high-resolution ...stereo camera (HRSC). Mars Express is now in its extended mission phase, during which much of the remaining part of the Martian surface is envisaged to be covered in stereo and color. The HRSC instrument is designed to map the morphology, topography, structure and geologic context of the surface as well as atmospheric phenomena. This paper discusses the measurement principles and operations of the instrument as well as the acquisition, calibration and processing of regional and global data sets. As HRSC is a push-broom scanning instrument with nine CCD line detectors mounted in parallel on a focal plane, its unique feature is the ability to obtain near-simultaneous imaging data at high resolution, with along-track triple stereo, four colors and five different phase angles, avoiding any time-dependent variations of the observing conditions. The HRSC spatial resolution is 10
m/pixel at the nominal periapsis altitude of 250
km, with an image swath of 53
km, and 2.3
m/pixel for an additional framing CCD device, called super resolution channel (SRC), practically working as an additional tenth channel of the HRSC and yielding nested-in black and white images for studies of small-scale geologic features. The sub-pixel accuracy of the three-dimensional point determination allows the derivation of digital terrain models (DTMs) with a grid size of up to 50
m and a height accuracy of a single pixel with up to 10
m, thus enabling us to carry out detailed quantitative analyses of the surface structure. The HRSC (1) bridges the gap between the medium–high-resolution Viking imagery and the very-high-resolution Global Surveyor mission, thus providing geological context, and (2) fills the gaps in the three-dimensional coverage and DTM grid of the MOLA laser altimetry data, and (3) helps characterize landing sites for in-situ measurements. HRSC also builds the basis for extended compositional mapping when combining spectral information with topographic photomaps over large areas. So far the HRSC measurements have made a significant contribution to the study of the evolution of volcanism and the role of water and ice throughout the Martian history.
We have investigated 12 prominent regions on Mars in detail with respect to their geologic evolution through time on the basis of detailed geologic mapping exercises and determining age relationships ...through crater counting techniques using imagery. New data in combination with previously obtained data have been analyzed by way of a refined method of cratering age extraction that also gives fine details of periods of resurfacing. We have found that there has been volcanic and fluvial/glacial geologic activity on the Martian surface at all times from >
4
Ga ago until today. This activity shows episodic pulses in intensity of both volcanic and fluvial/glacial processes at ~
3.8–3.3
Ga, 2.0–1.8
Ga, 1.6 to 1.2
Ga, ~
800 to 300
m.y., ~
200
m.y., and ~
100
m.y., and a possible weaker phase around ~
2.5–2.2
Ga ago. In between these episodes, there was relative quiescence of volcanic and/or fluvial/glacial activity. The episodes we find on the Martian surface in the crater frequency analyses of HRSC, MOC and THEMIS data coincide with some age groups of the Martian meteorites (~
1.3
Ga, ~
600–300
m.y., ~
170
m.y.). It appears that the surface activity expressions and their episodicity are related to the interior evolution of the planet when convection in the asymptotic stationary state changes from the so-called stagnant-lid regime to an episodic behavior. Similarities in episodic behavior are found for the other terrestrial planets: Venus, the Earth's moon, and the Earth itself suggesting a common general relationship in the evolutionary tracks.
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