Seismic Instrument for Asteroids (SIA): a seismometer based on geophone sensors for the RAMSES mission to Apophis

The internal structure of small asteroids (diameter < 1 km) remains poorly known, and recent spacecraft/surface interactions performed by the Osiris-REX and Hayabusa2 missions produced unexpected results about their physical properties.

What is the level of macro- and micro-porosity? What are the cohesive forces? Are the bodies stratified, heterogeneous or more homogenous? The answers to these questions have strong implications for both the long-term evolution of these bodies and for planetary defense.

Seismology experiments on such objects are difficult due to the low gravity and the possible small amount of natural seismic sources on these objects. However, during its pass close to the Earth in 2029, seismic activity will be generated in the asteroid Apophis by tidal stresses. This unique opportunity of natural seismic sources is exploited by the SIA instrument concept, which is planned to be deployed to the surface of the asteroid by the ESA RAMSES mission before the close encounter of Apophis with the Earth.

We first present and justify both the science case and the concept of operations of the seismic measurements on Apophis during the close encounter with the Earth. We then describe the instrument itself by presenting the current development status and system budgets. Finally, we discuss the lander platform requirements to reach the seismometer measurement performances and the science objectives.