Soviet Lander and Magellan Data Point toward Earthlike Venus Geochemistry and Volcanology, with Some Differences, and Many Questions

Introduction: Seven successful Soviet Venus landers reported compositional information on Venus surface rocks [1-3], and Magellan SAR discovered a wide range of familiar Earthlike volcanic landforms amidst a partially disimilar tectonic landscape. The landers produced compositional data and surface imagery consistent with orbital views indicating or suggesting volcanic landing sites associated with a variety of tectonic environments, including what appears to be boh rift and hotspot styles of volcanism [4]. The precision of the lander chemical analyses was poor [5]; only three landers reported major element compositions for most major oxides assessed by X-ray fluorescence, but not Na2O at all. Some landers also reported K, U, and Th determined by gamma ray emissions. Venera 8, the first successful lander, reported such high amounts of K2O that it was definitively concluded that Venus has an extremely differentiated crust, with K attaining a couple hundred times CI chondrite abundances. Granite was the preferred interpretation. Reassessments of Soviet geochemistry data: Kargel et al. [4] provided a more complete assessment of the Soviet data in conjunction with RADAR imagery and concluded that alkaline volcanic rocks may be more common on Venus than on Earth, and the Venera 8 sample was possibly one of those (while not ruling out a granite interpretation). Treiman [5] produced the most complete assessment of the full impact of instrumental errors on the possible interpretations, preferring more conservative 2-σ errors (95% confidence limits) as is standard in geochemistry. Analysts of the Venus data agree that they indicate a silicate body having a metallic Fe-rich core and FeO-rich mantle and that the crust is heterogeneous and includes parts that are highly differentiated relative to the mantle. I reiterate and support what Treiman stated about the limitations of interpretations due to large measurement errors, but the figures below [from 4] use 75% error bars. Certain conclusions are probable at 75% limits of confidence [4]; fewer things can be concluded at 95% limits of confidence [5] (Table 1). In fact some really profound things can be stated with 95% confidence (or greater); more things can be concluded with 75% confidence, which is not great confidence, but it is enough to start framing some hypothesis for future investigation by new Venus probes. Among the findings is that at 75% confidence, Venus may have a far greater incidence of highly alkaline volcanism than on Earth, but overall, Venus seems Earthlike in composition [5] (Table 1).