Since landing on Mars, the NASA InSight lander has witnessed 8 Phobos
and one Deimos transit. All transits could be observed by a drop in the
solar array current and the surface temperature, but more surprisingly,
for several ones, a clear signature was recorded with the seismic
sensors and the magnetometer. We present a preliminary interpretation of
the seismometer data as temperature induced local deformation of the
ground, supported by terrestrial analog experiments and finite-element
modelling. The magnetic signature is most likely induced by changing
currents from the solar arrays. While the observations are not fully
understood yet, the recording of transit-related phenomena with high
sampling rate will allow more precise measurements of the transit times,
thus providing additional constraints for the orbital parameters of
Phobos. The response of the seismometer can potentially also be used to
constrain the thermo-elastic properties of the shallow regolith at the
landing site.