486 publications from this institution
The potential is described of a candidate Mars Observer altimeter for determining dielectric properties of Mars regolith. It is pointed out that it is straightforward to use the time between altimeter pulse trains for passive radiometry (hence dielectric properties) and roughness can be derived. Given the mission plan the whole surface can be mapped at least three times, yielding data on seasonal variability.
The Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI) mission described herein has been selected for flight to Venus as part of the NASA Discovery Program. DAVINCI will be the first mission to Venus to incorporate science-driven flybys and an instrumented descent sphere into a unified architecture. The anticipated scientific outcome will be a new understanding of the atmosphere, surface, and evolutionary path of Venus as a possibly once-habitable planet and analog to hot terrestrial exoplanets. The primary mission design for DAVINCI as selected features a preferred launch in summer/fall 2029, two flybys in 2030, and descent sphere atmospheric entry by the end of 2031. The in situ atmospheric descent phase subsequently delivers definitive chemical and isotopic composition of the Venus atmosphere during a cloud-top to surface transect above Alpha Regio. These in situ investigations of the atmosphere and near infrared descent imaging of the surface will complement remote flyby observations of the dynamic atmosphere, cloud deck, and surface near infrared emissivity. The overall mission yield will be at least 60 Gbits (compressed) new data about the atmosphere and near surface, as well as first unique characterization of the deep atmosphere environment and chemistry, including trace gases, key stable isotopes, oxygen fugacity, constraints on local rock compositions, and topography of a tessera.
Abstract In this work we discuss various selected mission concepts addressing Venus evolution through time. More specifically, we address investigations and payload instrument concepts supporting scientific goals and open questions presented in the companion articles of this volume. Also included are their related investigations (observations & modeling) and discussion of which measurements and future data products are needed to better constrain Venus’ atmosphere, climate, surface, interior and habitability evolution through time. A new fleet of Venus missions has been selected, and new mission concepts will continue to be considered for future selections. Missions under development include radar-equipped ESA-led EnVision M5 orbiter mission (European Space Agency 2021), NASA-JPL’s VERITAS orbiter mission (Smrekar et al. 2022a), NASA-GSFC’s DAVINCI entry probe/flyby mission (Garvin et al. 2022a). The data acquired with the VERITAS, DAVINCI, and EnVision from the end of this decade will fundamentally improve our understanding of the planet’s long term history, current activity and evolutionary path. We further describe future mission concepts and measurements beyond the current framework of selected missions, as well as the synergies between these mission concepts, ground-based and space-based observatories and facilities, laboratory measurements, and future algorithmic or modeling activities that pave the way for the development of a Venus program that extends into the 2040s (Wilson et al. 2022).
A geometric model for the excavation and modification of simple crater development is presented. Modification is modelled by considering the relative dimensions and geometries of the final crater and the transient cavity formed by excavation and displacement. The input parameters required are the rim crest diameter of the final crater, the depth to autochthonous basement, the rim crest height and the outer rim slope. The model calculates the diameter of the final crater at the original ground plane, the dimensions of the transient cavity and the rim crest volume difference between the final and transient cavities. This volume is considered to be the material which slumped off the unstable, overheightened transient cavity wall during modification and corresponds to the observed volume of the breccia lens within the final crater. Excavation is approximated by a steady state Z model, with the diameter of excavation equivalent to the previously modelled diameter of the transient cavity at the original ground plane, the center of flow taken as 1 projectile diameter, and Z = 2.5–3.0. The Z model predicts such parameters as the depth and volume of excavation, which can be compared with observational data. The applicability of the model has been tested with data from Meteor and Brent craters. In the case of Meteor, the modelled final crater diameter at the original ground plane is within 26 m of the observed value and the modelled breccia lens and the rim crest volumes of the final true crater are within 9.5% and 2.5%, respectively, of observed values. The results of the Z model for Meteor crater, with Z = 2.8 ± 0.1, give results consistent with observational data on the depth and volume of excavation. The correspondence for the more degraded Brent crater is less precise, as there is greater uncertainty in the input parameters. It is possible, however, to match the model parameters with the breccia lens volume and published estimates of original dimensions. The modelled excavated volumes for Meteor and Brent are 58% and 55%, respectively, of the transient cavity volume below the original ground plane. In the absence of additional observational data for further testing, it is concluded that the model may provide first‐order spatial information on the formation of simple craters.
Shield volcanoes are common landforms on the silicate planets of the inner Solar System, and a wide variety have recently been documented on Venus by means of Magellan observations. In this report, we emphasize our recently completed morphometric analysis of three representative Icelandic lava shields: the classic Skjaldbreidur edifice, the low-reflief Lambahraun feature, and the monogenetic Sandfellshaed shield, as the basis for comparison with representative venusian edifices (greater than 60 km in diameter). Our detailed morphometric measurements of a representative and well-studied set of Icelandic volcanoes permits us to make comparisons with our measurements of a reasonable subset of shield-like edifices on Venus on the basis of Magellan global radar altimetry. Our study has been restricted to venusian features larger than approximately 60 km in basal diameter, on the basis of the minimum intrinsic spatial resolution (8 km) of the Magellan radar altimetry data. Finally, in order to examine the implications of landform scaling from terrestrial simple and composite shields to larger venusian varieties, we have considered the morphometry of the subaerial component of Mauna Loa, a type-locality for a composite shield edifice on Earth.
The present investigation has the objective to analyze the information collected by the Soviet Venera 9, 10, 13, and 14 lander spacecraft imaging systems. The analysis is to make a systematic comparison with other planetary surfaces possible, and an improved understanding of the surface of the planet Venus is to be provided. Attention is given to the imaging systems and transformation methods, observations, the observed characteristics of Venera lander sites, and an interpretation of the geological processes responsible for the features observed in the Venera panoramas. It is concluded that the present Venus environment is considerably different in terms of temperature, pressure, and atmosphere composition from the present terrestrial subaerial environment.
Near-polar craterforms have been observed on Mars since Mariner 9. Hodges and Moore [1,2] described the implications of these apparently volcanic features and suggested that several were formed as a consequence of magma-ice or magma-water interactions. Indeed, they proposed that the feature illustrated in Fig. I represents a hydromagmatic explosion crater or maar, indicating interaction of ground-ice and/or water with magma in the higher Northern hemisphere latitudes of Mars. The advent of Mars Orbiter Laser Altimeter (MOLA) topographic information 161 for several of the putative volcanic craterforms described in [1,2] allows a reconsideration of their formation mechanisms. We have exploited MOLA's near-centerline cross-sections from the Science Phasing Orbit phase of the Mars Global Surveyor (MGS) mission to analyze the geometric properties of these features as constraints on their modes of origin and subsequent modification histories. From our preliminary analyses, we believe there is evidence these features may have been formed by effusive, lava shield building eruptions, and not hydromagmatic events. Furthermore, geometrical constraints indicate that some of the near-polar craterforms are geologically youthful.
