Venus Dynamics Tracer (VdT) - a mission dedicated for in-situ measurements of the Venus atmosphere.

Recent Venus missions (Venus Express and Akatsuki) provided a large-scale view of Venus atmosphere and discovered new phenomena, such as high-altitude extension of the mountain wave to the cloud layer and a dawn-dusk asymmetry in the ionospheric motion.  The superrotation of the cloud layer is assumed to be driven by the thermal tide but its relation to any meridional convection or waves is still unknown.  The key to understand all these phenomena is to determine the multi-step re-distribution of the absorbed solar radiation to other forms of energy: (1) internal energy; including temperature, latent heat, and chemical energy (2) kinetic energy both in large scale flows/waves and in minor deviations of convection motions, (3) electric energy including ionization.

To understand how the motion of Venus atmosphere is driven by the energy originating from the absorption of solar radiation, we proposed Venus Dynamics Tracer (VdT), a mission for in-situ measurements, as a response to the ESA call for new M-class missions.  Specific targets were two major energy absorption regions: the cloud layer and the ionized upper atmosphere. The scientific goals were to investigate (a) the roles of the vertical and meridional circulation in maintaining major atmospheric dynamics near the cloud layer where visible light is absorbed and drives the vertical motions of the air, and to understand the (b) global dynamics of ions and neutrals in the upper atmosphere where EUV is absorbed both by neutrals and ions and where energy and momentum are transferred between them. 

For the first target, multiple-balloons are deployed for in situ observations with supporting camera/s on an orbiter giving global context. For the second target, the motions of ions and neutrals are directly measured.  This presentation discusses required measurements to answer the scientific goals.