Lander Radioscience in the twenties - Rotation of Mars and Positioning of the Surface Platform.

The Lander Radioscience experiments are designed to obtain coherent two-way Doppler measurements from the radio link between a lander on Mars (the ESA-ROSCOSMOS ExoMars 2020 Surface Platform or the NASA 2018 InSight spacecraft) and the Earth over at least one Martian year. The Doppler measurements will be used to observe the orientation and rotation of Mars in space (precession, nutations, and length-of-day variations), as well as possibly polar motion, depending on the lander position. The ultimate objective is to obtain information on the Martian interior and on the sublimation/condensation cycle of atmospheric CO₂. Rotational variations will allow us to constrain the moment of inertia of the entire planet, including its mantle and core, the moment of inertia of the core, and seasonal mass transfer between the atmosphere and the ice caps.

Besides, the LaRa transponder on ExoMars2020 could allow to accurately determining the position of the lander within a very short time after the starting of operations. An early estimate of the lander location will certainly improve the quality of the science analysis (for instance by making easier the recognition of the geological features seen on the lander's pictures) and allow high-resolution cameras from spacecraft like MRO to correctly target the lander.