Studying the Inner Heliosphere Using Radio Signals Transmitted From Spacecraft Orbiting Mars

Abstract In this campaign, we used very long baseline interferometry (VLBI) radio telescopes to track the carrier radio signal transmitted from spacecraft orbiting Mars during the Mars solar conjunction. The campaign extended from September to November 2021 and targeted the Mars Express (MEX) and Tianwen‐1 (TIW) spacecraft. The aim was to study the structure of the solar corona within 40 solar radii using the radio sounding technique developed by the Planetary Radio and Doppler Experiment (PRIDE). Previous work by the group has studied the effect of the solar wind and interplanetary scintillation on spacecraft signals at a large range of solar elongations. Here, we apply the same methodology to characterize the inner regions of the solar wind and attempt to capture the formation of transient solar phenomena such as solar flares or coronal mass ejections (CMEs). We found that the phase scintillation measurements fit the expected model of the electron content for the line‐of‐sight very close to the Sun. Experimental outliers, where the scintillation results deviated significantly from the expected electron content model, were compared with ancillary data from the LASCO C2 and C3 coronagraph instruments and found to correspond directly to solar transient events.