P22A-01 INVITED
Venus Exploration Goals, Investigations and Priorities
Data from the Venera, Pioneer Venus, Magellan and Venus Express missions have provided ample evidence that Venus is a complex terrestrial planet, providing a unique opportunity to study the coupling between interior, surface and atmospheric processes. Our knowledge of venusian atmospheric processes will be further enhanced by data from the upcoming Venus Climate Orbiter mission. However, critical questions on the evolution of the atmosphere, surface and interior of Venus will persist, questions that would allow us to better constrain the evolution of habitable environments in our solar system and beyond. In particular, the history of water on Venus is poorly understood, with the duration of the existence of a venusian ocean a fundamental unknown. The Venus Exploration Analysis Group (VEXAG) has produced a community white paper that describes and prioritizes scientific goals, objectives, and investigations. Many of the scientific goals are addressable in the near-term, with a combination of research and analysis of existing datasets, experimentation, and new missions to Venus.
P22A-02 INVITED
The Surface of Venus and Implications for its Geological and Geodynamical Evolution: The View Before Venus Express and Outstanding Questions for the Future
Prior to the Venera 15/16 and the Magellan missions to Venus, a wide range of ideas existed concerning the nature of the surface of Venus, the geological processes currently operating there, their link to interior processes, the implied geological and geodynamical history of the planet, and how all this compared with the nature and history of other terrestrial planetary bodies. The history of exploration of the surface of Venus represents the acquisition of data with increasing spatial and areal coverage, culminating in the near-global high-resolution image, altimetry, physical property and gravity data obtained by the Magellan mission. Among the most fundamental findings of the global Magellan image data are: 1) that volcanism and tectonism represent the most abundant geological processes operating on the observed surface, 2) that the styles and abundance of volcanism and tectonism combine attributes of both the Earth (e.g., very heavily tectonically deformed regions such as tessera) and the smaller terrestrial planetary bodies (e.g., vast volcanic plains deformed by wrinkle ridges), 3) that the distribution and nature of impact craters precludes active plate tectonics despite many Earth-like tectonic features (e.g., folded mountain belts), 4) that some features (e.g., coronae) are somewhat unique to Venus and may provide important information on mantle convection and lithospheric evolution processes, 5) that the number of impact craters is very small, indicating that the surface geological record is very young, less than 20% of the history of the planet itself, 6) that 80% of the geological record of Venus is no longer obviously preserved in the surface morphology, but may be preserved in the surface rocks, 7) that the distribution and state of preservation of existing impact craters may be consistent with a range of catastrophic resurfacing models, and 8) that the geological record and sequence of events can be correlated with geophysical data to assess crustal thickness variations and mantle convection patterns. The relationships of major elements of global topography and the sequence of events in the observed geological history (as recorded by major geologic units and structures) suggest that much of the current long-wavelength topography of Venus (tessera highlands and lowlands with regional plains) may have formed prior to emplacement of regional plains and been preserved since that time. These observations may favor evolutionary geodynamic models that are characterized by changes in geological style and rates, and may involve non-linear heat loss mechanisms that could have profound influence on the atmosphere. Although the observed surface of Venus dates from relatively recent planetary history, comparative planetology permits inferences to be made about the major stages in the earlier history of Venus. The evolution of the understanding of the surface from early speculations to present observations and interpretations provides an important context for: 1) establishing the relationships of the surface of Venus to the nature of the atmosphere and its evolution as assessed by Venus Express, 2) the comparison of the geological features and history of Venus relative to the Moon, Mars, Mercury and the Earth, and 3) defining the major outstanding problems and questions to be addressed by future experiments and missions to Venus.
P22A-03
Possible recent volcanoes and coronae on Venus: Emissivity anomalies, lithospheric thickness, and resurfacing
Extensive calibration of the Venus Express near infrared imaging data, which currently covers most of the southern hemisphere, shows regions of anomalously high or low thermal emission (Mueller et al., 2008; Helbert et al., 2008). Typically high thermal emission anomalies are associated with volcanoes or corona, and lows associated with tessera. Mueller et al. (2008) and Helbert et al. (2008) interpret these anomalies as likely to be associated with either compositional variations or relatively recent volcanic flows that are less weathered. They believe that thermal variations are unlikely to persist over the duration of data collection. In this study we focus on anomalies associated with coronae and volcanoes, and examine additional data that could distinguish between compositional variations, lack of weathering on recent flows, or potentially some combination of the two. Mueller et al. (2008) describe 6 volcanoes or coronae with high emissivity anomalies. Of these, 3 are in Themis Regio, 2 in Dione Regio, and one in Imdr Regio. All of these areas have been identified as likely hotspots with possible current mantle upwelling. The estimated elastic thickness is quite small (0-10 km) at Themis and Dione, consistent with an interpretation of active volcanic centers. The resolution of the gravity data at Imdr is too low to get a reliable elastic thickness estimate, but the large depth of compensation does suggest the presence of a plume. We also examine some flows associated with Atete Corona in Parga Chasma that appear to have low emissivity. Atete is 600 km in diameter and has an elastic thickness of ~45 km. We interpret this region as an area of unusual composition, possibly due to melting in a region of delamination (Elkins-Tanton et al., 2007). Further evidence for the interpretation that these areas of anomalous emissivity may be recent comes from analysis of the resurfacing history of Venus. Phillips and Izenberg (1995) examined the distribution of craters with and without haloes (thin ejecta blankets deposited by the wind) and the degree of modification of haloes. They found two regions with both low spatial crater densities and a large proportion of embayed and tectonized craters. They interpret these as areas of relatively recent resurfacing. One is the Beta-Atla- Themis triangle, which is known for its concentration of volcanic features, and the other is the Lavinia Plantia region. Themis and Dione Regios and Atete Corona lie within these regions, as do some of the areas of low emissivity tessera. Idunn volcano in Imdr is the lone exception, but it does lie on the transition from possibly older areas to younger areas. These lines of evidence strongly suggest a relatively recent origin for the emissivity anomalies associated with coronae and volcanoes.
P22A-04
Global Mapping of Venus' Atmosphere Using Accumulated Projections of Virtis Venus Express Observations
The VIRTIS instrument onboard Venus Express has been using its Mapping channel successfully since the Venus orbit insertion on 11th April 2005. The hyper-spectral images obtained in the near-Infrared and Visible cover a wide spectral range (5um-250nm) with good sampling capabilities, which make them highly useful for the study of morphology, dynamics and composition of the atmosphere and the surface. Single observations performed by VIRTIS typically cover only a fraction of the Venus' disk and thus they provide instantaneous information of local features. We are now investigating a new approach to study the global morphology of Venus' atmosphere by linking the current 3-dimensional VIRTIS measurements (2 spatial + 1 spectral) with their evolution in time, thanks to the good coverage of the instrument, mapping same regions at different times and with different conditions (season, local solar time, etc). We present high quality global distribution maps of radiance over the whole planet, with results showing the different morphology of various layers of the atmosphere, e.g. Oxygen Nightglow emission at 1.27um in the upper mesosphere and deep atmosphere clouds observed at 1.74um. In addition, we can compare different emissions probing the same layer, as in the case of the radiance at 1.74um/2.3um and the Thermal Brightnesses at 3.8um/5um. All these global distribution maps show interesting dependences with latitude and local time (or longitude) giving useful information for the study of the global morphology of Venus' atmosphere. Other products derived by the new system such as time series, coverage maps, radiance variation plots and radiance stability maps can also lead to a more detailed analysis and a better understanding of the global dynamics and morphology of the atmosphere.
P22A-05
Horizontal and Vertical Distribution of SO2 in the Venus Clouds From SPICAV UV spectrometer.
The two bands of UV absorption of SO2 at 180-220 and 280-300 nm may be used to detect SO2 in the upper atmosphere of Venus. On board Venus Express mission, the UV spectrometer (118 - 320 nm, resolution 1.5 nm) of SPICAV is dedicated to nadir viewing, limb viewing and vertical profiling by stellar and solar occultation. In the solar occultation mode, SO2 is seen up to 100 km with a mixing ratio of about 1 ppmv, a puzzling result since it should be photo-dissociated at this altitude. In the stellar occultation mode which is performed at night, SO2 is also seen up to 100 km, possibly resulting from the evaporation of H2SO4 cloud droplets. In nadir orientation, SPICAV UV analyzes the albedo spectrum (solar light scattered back from the clouds) to retrieve SO2, and the distribution of the UV-blue absorber (of still unknown origin) on the day side with implications for cloud structure, and atmospheric dynamics. The abundance of SO2 and its scale height are determined by comparison of the measured albedo spectrum with the output of a radiative transfer code, yielding horizontal distributions. Results obtained from the various modes of observation will be compared.
P22A-06
Get the heat on Obtaining high temperature emissivity measurements in support of the analysis of surface data from VIRTIS on VenusExpress
Analyzing the surface composition of Venus from remote-sensing measurements is a challenging task. Recently we have reported on brightness variations in the near infrared wavelength range observed with VIRTIS on VenusExpress. Our implication is that these brightness variations might be correlated to emissivity variations of the surface material. The next step to verify this hypothesis is to obtain data in the relevant spectral range at temperatures typical for the surface of Venus. We are currently developing a Planetary Emissivity Laboratory (PEL) at Deutsches Zentrum für Luft- und Rahmfahrt (DLR) in Berlin. The PEL allows measuring the emissivity of planetary analog materials grain sizes fractions from less than 25 microns all the way to bulk samples and at temperatures of more than 400°C, typically for the surface of Venus. The PEL development follows a multi-step approach. We are currently installing a new calibration target that will allow obtaining emissivity data on the full range from 1 to 50 microns with a usable signal-to-noise ratio. Here we will present first data in the range from 1 to 1.4 microns which covers the atmospheric windows used for the surface observations from VIRTIS on VenusExpress. We will focus especially on which measurements are necessary to verify our earlier hypotheses of compositional variations on the surface of Venus.
P22A-07
Japanese Venus Climate Orbiter in 2010
Venus Climate Orbiter (VCOFProject Code Planet-C) is the first Japanese Venus orbiter to be launched in
2010. It aims at studying the atmospheric dynamics of Venus. In this talk we will report its engineering aspect
to meet its science purposes, and also present the present status of the VCO development. We have
finished the Proto-Model integration test of major components of VCO in December 2007. In March 2008, we
finished the CDR for the phase-up (to Phase D). The flight model development will be finalized by 2009 and
the final integration test will be done during whole 2009.
http://www.jaxa.jp/article/interview/vol34/index_e.html
P22A-08
A Venus Flagship Mission: Exploring a World of Contrasts
Results from past missions and the current Venus Express Mission show that Venus is a world of contrasts, providing clear science drivers for renewed exploration of this planet. In early 2008, NASA's Science Mission Directorate formed a Science and Technology Definition Team (STDT) to formulate science goals and objectives, mission architecture and a technology roadmap for a flagship class mission to Venus. This 3- to 4 billon mission, to launch in the post 2020 timeframe, should revolutionize our understanding of how climate works on terrestrial planets, including the close relationship between volcanism, tectonism, the interior, and the atmosphere. It would also more clearly elucidate the geologic history of Venus, including the existence and persistence of an ancient ocean. Achieving these objectives will provide a basis to understand the habitability of extra solar terrestrial planets. To address a broad range of science questions this mission will be composed of flight elements that include an orbiter that is highlighted by an interferometric SAR to provide surface topographic and image information at scales one to two orders of magnitude greater than that achieved by any previous spacecraft to Venus. Two balloons with a projected lifetime of weeks will probe the structure and dynamics of the atmosphere at an altitude of 50 to 70-km. In addition, two descent probes will collect data synergistic to that from the balloon and analyze the geochemistry of surface rocks over a period of hours. The technology road map focuses on key areas of science instruments and enabling engineering to provide greater in situ longevity in the hostile Venus environment.