Global deformation and internal structure of Venus in the frame of its exploration missions

The planet Venus is called the twin sister of the Earth since it has a similar radius and density. The internal structure of the two planets are therefore assumed to be close with an iron rich core, a magnesium silicate mantle and a silicate crust. Despite these similarities Venus lacks plate tectonics and an internal magnetic field. Its atmosphere is thick, dense and rich in CO2. Venus also has high surface temperature and pressure of 737 K and 93 bars, respectively. The known facts about Venus are drawn from its mass, radius, surface temperature, topography and gravity field. Many information are still unknown as its core structure, mantle viscosity and extent of its activity driven from mantle plumes. This planet is of interest since it evolved very differently from its twin planet andrecent proof of volcanic activity have been observed. In the frame of the future Venus exploration missions EnVision and VERITAS, we investigate the internal structure of the planet and assess the detection of its geophysical activity. Firstly, we use the mass, the moment of inertia, the tidal Love number k2 and an expected range of the quality factor Q derived from geophysical and geodetical observations to select, using a Monte-Carlo approach, the most likely interior models of Venus. The selected models made of four or five layers are radial descriptions of Venus rheological parameters. Our selected models show that significant contrasts in the viscosity are required between the upper mantle and the lower mantle and additionally favor a sulfur free core. Secondly, we estimate the effect of a Venus-quake on the surface displacement and gravity variation. To do so we suppose the occurrence of a dip-slip rifting on Venus of the same geometry and magnitude as the 2005 Manda Hararo-Dabbahu seismic event in the East-African rift system on Earth. After validating our computation for the Earth, we apply the same dip-slip model on a model of Venus and calculate the coseismic and postseimic rebounds. We show that, with future EnVision and VERITAS altimetry data, the rifts on Venus will be better mapped and therefore more information on its geological activity should be obtained. Additionally, the surface relaxation after a seismic event will be observed with Repeat Pass Interferometry (RPI) performed with VERITAS which will possibly give indications on the magnitude and depth of a seismic dislocation.