Science and Exploration of a Jupiter Trojan Asteroid in the solar-power sail mission

Jupiter Trojan asteroids are located around the Sun-Jupiter Lagrange points (L4 or L5), and most of them are classified as D- or P-type, considered as volatile rich materials with rocks, water ices, and organics. However, the origin and evolution, composi- tion and physical conditions of these bodies still remain unknown. Jupiter Trojans are the missing links of ma- terials that originates from inner and outer solar system, and they are also intermediate size to undergo aqueous and thermal alteration between primitive smaller and evolved larger bodies. They are the key targets to un- derstand the evolution process and the chemical radial distribution in the solar system. An engineering mission to a Jupiter Trojan asteroid is being studied in Japan using a hybrid propulsion system of a large area solar-power sail (SPS) and a sophisticated ion engine [1]. After arriving there, the asteroid will be investigated for scientific purpose and for landing site selection by remote sensing. A lander will be deployed to land on the asteroid surface and conduct in situ bservations. A Jupiter Trojan multi-flyby mission (LUCY) [2] has been selected as the next Discovery class mission, which aims at understanding the variation and diversity of Jupiter Trojans, contrary to the SPS mission which will rendezvous and land on the asteroid and conduct in-depth measurements. The SPS mission is jointly studied between engineers and scientists both from Japan and Europe [3]. We will present here the key scientific objectives and the strawman payloads for the SPS mission.