On a mechanism of polarization origin at the polar regions of Jupiter

We propose the following mechanism of linear polarization origin at Jupiter’s polar regions: the principal contribution in polarization is made by the light reflected by cloud layer and then scattered by stratospheric aerosol particles. The linear polarization distributions along the central meridian for two spectral bands (0.46 μm and 0.70 μm) are calculated. They are in good qualitative agreement with observational data. The mean scattering particle radius is estimated as rmean = 0.5 μm

What is the Oxygen Isotope Composition of Venus? The Scientific Case for Sample Return from Earth’s “Sister” Planet

Venus is Earth’s closest planetary neighbour and both bodies are of similar size and mass. As a consequence, Venus is often described as Earth’s sister planet. But the two worlds have followed very different evolutionary paths, with Earth having benign surface conditions, whereas Venus has a surface temperature of 464 °C and a surface pressure of 92 bar. These inhospitable surface conditions may partially explain why there has been such a dearth of space missions to Venus in recent years.The oxygen isotope composition of Venus is currently unknown. However, this single measurement (Δ17O) would have first order implications for our understanding of how large terrestrial planets are built. Recent isotopic studies indicate that the Solar System is bimodal in composition, divided into a carbonaceous chondrite (CC) group and a non-carbonaceous (NC) group. The CC group probably originated in the outer Solar System and the NC group in the inner Solar System. Venus comprises 41% by mass of the inner Solar System compared to 50% for Earth and only 5% for Mars. Models for building large terrestrial planets, such as Earth and Venus, would be significantly improved by a determination of the Δ17O composition of a returned sample from Venus. This measurement would help constrain the extent of early inner Solar System isotopic homogenisation and help to identify whether the feeding zones of the terrestrial planets were narrow or wide.Determining the Δ17O composition of Venus would also have significant implications for our understanding of how the Moon formed. Recent lunar formation models invoke a high energy impact between the proto-Earth and an inner Solar System-derived impactor body, Theia. The close isotopic similarity between the Earth and Moon is explained by these models as being a consequence of high-temperature, post-impact mixing. However, if Earth and Venus proved to be isotopic clones with respect to Δ17O, this would favour the classic, lower energy, giant impact scenario.We review the surface geology of Venus with the aim of identifying potential terrains that could be targeted by a robotic sample return mission. While the potentially ancient tessera terrains would be of great scientific interest, the need to minimise the influence of venusian weathering favours the sampling of young basaltic plains. In terms of a nominal sample mass, 10 g would be sufficient to undertake a full range of geochemical, isotopic and dating studies. However, it is important that additional material is collected as a legacy sample. As a consequence, a returned sample mass of at least 100 g should be recovered.Two scenarios for robotic sample return missions from Venus are presented, based on previous mission proposals. The most cost effective approach involves a “Grab and Go” strategy, either using a lander and separate orbiter, or possibly just a stand-alone lander. Sample return could also be achieved as part of a more ambitious, extended mission to study the venusian atmosphere. In both scenarios it is critical to obtain a surface atmospheric sample to define the extent of atmosphere-lithosphere oxygen isotopic disequilibrium. Surface sampling would be carried out by multiple techniques (drill, scoop, “vacuum-cleaner” device) to ensure success. Surface operations would take no longer than one hour.Analysis of returned samples would provide a firm basis for assessing similarities and differences between the evolution of Venus, Earth, Mars and smaller bodies such as Vesta. The Solar System provides an important case study in how two almost identical bodies, Earth and Venus, could have had such a divergent evolution. Finally, Venus, with its runaway greenhouse atmosphere, may provide data relevant to the understanding of similar less extreme processes on Earth. Venus is Earth’s planetary twin and deserves to be better studied and understood. In a wider context, analysis of returned samples from Venus would provide data relevant to the study of exoplanetary systems

Geologic interpretation of the near-infrared images of area SW of Beta Regio taken by the Venus Monitoring Camera

We analyze night-time near-infrared (NIR) images of Beta-Phoebe region obtained with the 1-μm channel of the Venus Monitoring Camera (VMC) onboard Venus Express. Comparisons with the results of the Magellan radar survey and the model NIR images show that the night-time VMC images provide reliable information on spatial variations of the NIR surface emission. Here we consider if tessera terrain has the different NIR emissivity (and thus mineralogical composition) in com- parison to the surrounding basaltic plains. This is done through the study of an area SW of Beta Regio where there is a massif of tessera terrain, Chimon-mana Tessera, surrounded by supposedly basaltic plains. Our analysis showed that 1-μm emissivity of tessera surface material is by 15 – 35 % lower than that of relatively fresh suppos- edly basaltic lavas of plains and volcanic edifices. This is consistent with hypothesis that the tessera material is not basaltic, maybe felsic, that is in agreement with the results of analyses of VEX VIRTIS and Galileo NIMS data. If the felsic nature of venusian tesserae will be confirmed in further studies this may have important implications on geochemical environments in early history of Venus. We have found that the surface materials of plains in the study area are very variegated in their 1-μm emissivity, which probably reflects variability of degree of their chemical weathering. We have also found a possible decrease of the calculated emissivity at the top of Tuulikki Mons volcano which, if real, may be due to different (more felsic?) composition of volcanic products on the volcano summit

Geologic interpretation of the NIR images taken by the Venus Monitorin Camera

Joint analysis of the VMC 1 micron surface radiation images for the Beta-Phoebe region, the results of Magellan radar survey and the model images of this region showed that the VMC images provided reliable information on spatial variations of the NIR radiation of the Venus surface, which can be interpreted in terms of geological characteristics of the studied area,including potential compositional differences between geologic units. In particular, our analysis showed that surface of several relatively small massifs of tessera terrain observed in the study area showed the 1 micron emissivity which is not noticeably different from that typical of surrounding basaltic plains. This may mean that these tesserae are composed of basalts or it can be a result of pollution of surface of tessera by the wind-blown fine debris brought from the surrounding plains. This controversy hopefully may be resolved in future studies if much larger tessera massifs will be imaged by VMC. Analysis of the VMC images of the mountain tops covered with the enigmatic radar-low-emissivity material suggests that its 1 micron emissivity do not significantly differ from the emissivity of basalts that is consistent with earlier published geochemical conlusions that it can be hematite, or magnetite, or pyrite. We have found that the radar-bright and radar-dark subunits of the basaltic regional plains dominating in the study area do not show noticeable difference in their 1 micron emissivity. This was interpreted as indication on rather similar composition of these two plains varieties and differences in their radar brightness are probably due to differences in their surface roughness. We did not find any indication on ongoing volcanic eruptions in the study area that probably may be due to low spatial resolution of the VMC imaging and/or to actual absence of the ongoing volcanic activity. In our future studies we plan to involve to the analysis the new data acquired in the continuing Venus Express mission and to apply techniques of quantitative analysis to the existing and future data

Geologic Analysis of the Surface Thermal Emission Images taken by the VMC Camera, Venus Express

Introduction. The Venus Monitoring Camera (VMC) onboard Venus Express takes images in 4 channels, one of which is centered at 1.01 μm. When the camera looks at the night side of Venus, this channel registers thermal emission from the planet surface from mid-southern to mid-northern latitudes [1]. Due to scattering of the emitted radiation in the atmosphere and the cloud layer, the effective spatial resolution in the surface images is ~50 km. Thus, modeling the atmospheric blurring is essential for this work. Here we report results of preliminary analysis of some VMC 1-μm images. Intensity of the surface thermal emission at 1 μm depends strongly on its temperature and thus on surface elevation as well as on surface emissivity and cloud opacity. But emissivity of the surface material depends also on surface texture and mineralogy so the image analysis can provide an information on these parameters. Also, if there is an ongoing volcanic eruption in the camera field of view, it might be noticed on the images

Geologic interpretation of the near-infrared images of the surface taken by the Venus Monitoring Camera, Venus Express

We analyze night-time near-infrared (NIR) thermal emission images of the Venus surface obtained with the 1-μm channel of the Venus Monitoring Camera onboard Venus Express. Comparison with the results of the Magellan radar survey and the model NIR images of the Beta-Phoebe region show that the night-time VMC images provide reliable information on spatial variations of the NIR surface emission. In this paper we consider if tessera terrain has the different NIR emissivity (and thus mineralogic composition) in comparison to the surrounding basaltic plains. This is done through the study of an area SW of Beta Regio where there is a massif of tessera terrain, Chimon-mana Tessera, surrounded by supposedly basaltic plains. Our analysis showed that 1-μm emissivity of tessera surface material is by 15–35% lower than that of relatively fresh supposedly basaltic lavas of plains and volcanic edifices. This is consistent with hypothesis that the tessera material is not basaltic, maybe felsic, that is in agreement with the results of analyses of VEX VIRTIS and Galileo NIMS data. If the felsic nature of venusian tesserae will be confirmed in further studies this may have important implications on geochemical environments in early history of Venus. We have found that the surface materials of plains in the study area are very variegated in their 1-μm emissivity, which probably reflects variability of degree of their chemical weathering. We have also found a possible decrease of the calculated emissivity at the top of Tuulikki Mons volcano which, if real, may be due to different (more felsic?) composition of volcanic products on the volcano summit