[P-CG20] Future missions and instrumentation for space and planetary science

[PCG20-07] The Next Generation small-body Sample Return mission: Seismology on Comets

Satoshi Tanaka², *Taichi Kawamura¹, Keisuke Onodera^1,3, Gaku Nishiyama⁴, Takeshi Tsuji⁵, Naoya Sakatani², Yuri Shimaki², Hiroyuki Kurokawa⁴, The Next Generation small-body Sample Return Working Group (1.Universite Paris Cite Institut de physique du globe de Paris CNRS, 2.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3.Earthquake Research Institute / The University of Tokyo, 4.The University of Tokyo, 5.Department of Systems Innovation, the University of Tokyo)

Keywords:Planetary Science, Comet, Seismology

Comets possess the memory of early history of the solar system and are regarded as a key to understand the evolution of the solar system and the planet formation. To better understand better comets and the origin and evolution of the solar system, we are now considering the New Generation Sample Return Mission to a comet. In addition to the sample return, a series of in-situ observations are planned and exploration of the internal structure of the comet is regarded as one of the key aims for the in-situ observation. In this study, we will focus on seismological approaches and discuss how seismology can contribute to the mission. For seismic observations under micro to zero gravity condition such as on a comet, coupling between the seismometer and the ground will be important. There is significant risk that the seismometer will be decoupled with ground motion and thus losing the coupling. In this study, we first evaluated the condition that our seismometer will be decoupled with the ground. We will then describe our strategy for seismic signals that will and will not decouple the seismometer from the ground. When the seismometer is not decoupled, classical seismic methods can be applied. We discuss here the possibility to use surface waves and scattered waves to explore the subsurface structure of the comet and its heterogeneous structure. On the other hand, when the seismometer will be decoupled from the ground, we evaluated if we can continue the observation after re-landing on the comet’s surface. For this, we calculated the long period normal modes of comet excited by Hayabusa 2’s SCI-like artificial impact and evaluated if such event will excite large enough free oscillation to be detected. Finally, we will describe the seismic observation system that we are proposing to the mission.