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Dr. Gregg: What Has She Been Up

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Dr. Gregg: What Has She Been Up On the Significance of Venusian Canali: Landing Site Selection Tracy K.P. Gregg, [email protected] Dept. of Geology, University at Buffalo, Buffalo NY 14260- 3050, USA Susan E.H. Sakimoto, [email protected] Space Science Institute, 4650 Walnut St., Suite 205, Boulder, CO, USA Venera-D Landing Site / Habitability October 2019 Venus Canali: What? wrinkle ridge Arcuate to sinuous troughs 101 – 103 km long Longest channel = Baltis Vallis, >6800 km long Almost constant widths (1 – 5 km) along lengths Limited branching (tributaries and distributaries rare) Similar to lunar sinuous rilles 20 km https://nssdc.gsfc.nasa.gov/imgcat/html/object_page/mgn_f45n019_1.html Venus Canali: Feeding the plains Moon Significance: similar to lunar sinuous rilles, likely contain the lava that created the Venus Venusian plains 10 km Rille lavas = Venusian plains VEGA & Venera Landers = composition of Venusian plains https://history.nasa.gov/SP-362/ch6.2.htm https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA00253 70 km Venus Canali: How? Kilauea, Hawaii Requires liquid to form May 2018 Lava Basalt? Something more exotic? carbonatite komatiite sulfur drained lava channels https://volcanoes.usgs.gov/volcanoes/kilauea/multimedia_chronology.html Venus Canali: How? Lava erosion vs. lava construction Erosion: thermal, mechanical, or both? Construction: collapsed lava tubes, drained lava channels? https://volcanoes.usgs.gov/volcanoes/kilauea/archive/multimedia/2001/Jul/2-5-12-14.shtml https://volcanoes.usgs.gov/volcanoes/kilauea/archive/multimedia/2007/2007_Sep.shtml Venus Canali: Construction Collapsed lava tubes Drained lava channels Mafic lavas basalt komatiite https://volcano.istad.org/2018/09/02/september-2-a-few-signs-of-life-deep-in-fissure-8/ Venus Canali: Erosion (mechanical) Natrocarbonatite Requires exotic lava compositions Lavas with low (<730 K) solidification temperatures carbonatite sulfur (Kargel et al., 1994) http://blogs.stlawu.edu/lengai/what-is-carbonatite/ Venus Canali: Erosion (thermal) ▪ Fully turbulent lava flows? (Wilson and Head, 1981) •high effusion rates Thermal erosion in terrestrial komatiites •low-viscosity lavas •efficient heat transfer •short eruption duration ▪ Laminar lava flows? •low, steady effusion rates •long eruption durations • thermal conduction McQueen (2005) downcutting Erosion vs. construction: Significance Turbulent lava erosion: •requires conditions not observed on Earth today •requires violently high effusion rates for entire eruption Laminar (thermal diffusion) lava erosion on Earth ~10 cm/day downcutting: no exotic lavas required http://volcano.oregonstate.edu/lava-tubes Venus canali: Parameter space example Input: Basalt lava (Barsukov, 1992) r = density = 3000 kg/m3 m = viscosity = 1 – 500 Pa s open-channel flow lava depth = 50 m channel width = 5 km Venus canali: Parameter space example Fully turbulent (mechanical erosion) requires exotic lavas (carbonatites, sulfur) Transitional, laminar regimes can be basalt (Sakimoto and Gregg, 2001) Venus landing sites: Land near canale (as safely as possible) ▪ Canali-fed plains lavas: what are they? ▪ Look for constructional levees ▪ Levees higher than surrounding plains ▪ Spatter ramparts ▪ Spillovers ▪ Bingham fluid behavior ▪ Look for layers exposed in canali walls (cf. Hadley Rille) ▪ Thick? Thin? Similar to Moon? Earth? ▪ Accurate canali dimensions https://www.isviews.geo.uni-muenchen.de/photos/fieldwork_2015/index.html References Barsukov, V.L., 1992, Venusian igneous rocks, in Venus Geology, Geochemistry and Geophysics, V.L. Barsukov, A.T. Basilevsky, V.P. Volkov and V.N. Zharkov, Eds., pp. 165-176, U. Arizona Press, Tucson. Kargel, J.S., R.L. Kirk, B. Fegley, Jr., and A.H. Treiman, 1994, Carbonate-sulfate volcanism on Venus? Icarus 112:219-252. McQueen, K.G., 2005, Ore deposit types and their primary expressions, in Regolith Expression of Australian Ore Systems, Edition 1, C.R.M. Butt, I.D.M. Robertson, K.M. Soctt and M. Cornelius, eds., pp. 1-14. Sakimoto, S.E.H. and T.K.P. Gregg, 2001, Channeled flow: Analytic solutions, laboratory experiments, and applications to lava flows, J. Geophys. Res. 106(B5):8629-8644. Venus Canali: Probably Basalt Venera / VEGA landers consistent with basaltic plains (Barsukov, 1992) Morphology Analogy with lunar sinuous rilles.
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