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ANALYSIS OF THE IMAGES OF THE VENUS SURFACE TAKEN BY THE VENUS MONITORING CAMERA, VENUS EXPRESS E.V. Shalygina, A. T. Basilevskya,b, W. J. Markiewicza, D.V. Titovc,a, W.J. F. Scholtend, Th. Roatschd, M.A. Kreslavskye, L.V. Morozf,d, N.I. Ignatievb,g, B. Fietheh, B. Osterlohh, H. Michalikh, N.L. Mironovb, J.W. Headi aMax-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany; bVernadsky Institute, RAS, 119991 Moscow, Russia; cESA-ESTEC, SRE-SM, Noordwijk H, The Netherlands; dInstitut für Planetenforschung, DLR, Berlin, Germany; eUniversity of California, Santa Cruz, CA, USA; fInstitut für Planetologie, Westfalische Wilhelms-Universität, Münster, Germany; gSpace Research Institute, RAS, Moscow, Russia; hIDA, Technische Universität, Braunschweig, Germany; iBrown University, Providence, RI, USA. Contact: [email protected] The Venus Monitoring Camera (VMC) is a part of the Venus Express payload. Takes images in 4 spectral channels; one centered at 1.01 μm registers the night-side thermal emission from the planet’s surface. Formal spatial resolution is 1–5 km/px, but because the surface radiation on its way to camera passes through the scattering atmosphere including clouds, the actual spatial resolution at the surface is about 50 km. So the VMC images look diffuse with brighter (higher radiation) and darker (lower radiation) spots. Brighter / darker may be due to the higher / lower surface temperature, that on Venus is a function of surface altitude (higher => colder). But another potential component of the effect is surface material emissivity. If the surface altitudes, the atmosphere optical properties and temperature lapse are known, then one can produce a model to calculate surface emissivity values from the VMC measurements. Beta Regio Chimon-mana Tessera and Tuulikki Mons volcano Topo, Topo,SAR, SAR,and andsimplified simplifiedgeologic geologicmaps mapsofofthe thestudy studyregion region Tuu Tuu==Tuulikki TuulikkiMons Mons Chi Chi==Chimon-mana Chimon-manaTessera Tessera We found that the 1- μm emissivity of surface of Chimon-mana Tessera is lower or than that of “unweathered” basaltic plains and the emissivity of the Tuulikki Mons top is lower than that of its slopes. Lower emissivity may suggest felsic composition Summit Slopes Lower emissivity of tessera terrain surfaces was also found based on analyses of VIRTIS data (Helbert et al. (2008), Mueller et al. (2008), Hashimoto et al. (2008), and Gilmore et al. (2011): Ancient “granitic” crust (?) Suggestion of felsic composition of Tuulikki summit finds support in its surface morphology : steep-sided dome (?) Steep-sided volcanic domes on Venus are often considered to be due to felsic composition of the lavas (e.g., Pavri et al., 1992; Fink et al., 1993) Structures similar to steep-sided domes were observed near the top of Sapas Mons volcano (Keddie, Head & 1994) and in other places. Felsic? Felsic domes on Earth: Novarupta rhyolite dome, Alaska 400 m It happens, however, that felsic products may be formed in other volcanic environments, including hot spot volcanism, e.g., Puu Waawaa trachyte dome, Hualalai volcano, Hawaii. 2 km Conclusions: • Analysis of the data taken by the VMC camera shows that Chimon-mana tessera has a lower 1-µm emissivity than that of “unweathered” plains suggesting its more felsic composition. Implications: Ancient “granitic” crust, oceans in the past? • The lower 1-µm emissivity was also found for the Tuulikki Mons volcano summit comparing of the main body of the volcano, whose general morphology is typical of a basaltic volcano. So the volcano summit material may be close to felsic and this suggestion is supported by the presence there of a feature resembling a steep-sided dome. • Formation of felsic lavas on Venus may be due to (1) differentiation within the magma chamber, (2) partial melting and assimilation of tesserae material by basaltic magma, or (3) remelting of the basaltic crust.