Spacecraft Reconnaissance of Asteroid and Comet Interiors (2015) 6019.pdf

CASTALIA – A MISSION TO A MAIN BELT COMET. G. H. Jones1, K. Altwegg2 , I. Bertini3, A. Bieler4, H. Boehnhardt5, N. Bowles6, A. Braukhane7, M. T. Capria8, A. J. Coates1, V. Ciarletti9, B. Davidsson10, C. Engrand11, A. Fitzsimmons12, A. Gibbings13, O. Hainaut14, M. Hallmann15, A. Herique16, M. Hilchenbach5, M. Homeister13, H. Hsieh17, E. Jehin18 W. Kofman16, L. M. Lara19, J. Licandro20, S. C. Lowry21, F. Moreno19, K. Muinonen22 , M. Paetzold23, A. Penttilä22, Dirk Plettemeier24, D. Prialnik25, U. Marboeuf 2, F. Marzari26, K. Meech27, A. Rotundi28,29, A. Smith1, C. Snodgrass30, I. Thomas6, M. Trieloff31, 1UCL Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK ( [email protected] ), 2U. Bern, CH, 3U. Padova, IT, 4U. Michigan, USA, 5MPS, Göttingen, DE, 6U. Oxford, UK, 7DLR, Bremen, DE, 8INAF/IAPS, Rome, IT, 9LATMOS/UVSQ, Guyancourt, FR, 10U. Uppsala, SE, 11CNRS, Paris, FR, 12QUB, Belfast, UK, 13OHB System AG, Bremen, DE, 14ESO, 15DLR, Bremen, DE, 16IPA/UJF, Grenoble, FR, 17Academia Sinica, Institute of Astronomy & Astrophysics, Taiwan, 18U. Liège, BE, 19IAA, Granada, ES, 20IAC, Tenerife, ES, 21U. Kent, Canterbury, UK, 22U. Helsinki, FI, 23U. Köln, DE, 24TU Dresden, DE, 25U. Tel Aviv, IL, 26 INFN, Padova, IT, 27IfA, Honolulu, USA, 28Università di Napoli “Parthenope”, IT, 29 INAF-IAPS, Roma, IT, 30Open U., UK, 31U. Heidelberg, DE

Main Belt Comets (MBCs), a type of Active Aster- Radio science, Subsurface radar, Dust impact detector, oid, constitute a newly identified class of solar system Dust composition analyser, Neutral/ion mass spec- objects. They have stable, asteroid-like orbits and some trometer, Magnetometer, and Plasma package. In addi- exhibit a recurrent comet-like appearance. It is be- tion to this, a surface science package is being consid- lieved that they survived the age of the solar system in ered. a dormant state and that their current ice sublimation driven activity only began recently. Buried water ice is At the moment, MBC 133P/Elst-Pizarro is the best- the only volatile expected to survive under an insulat- known target for such a mission. A design study for the ing surface. Excavation by an impact can expose the Castalia mission has been carried out in partnership ice and trigger the start of MBC activity. We present between the science team, DLR and OHB System AG. the case for a mission to one of these objects, to be This study looked at possible missions to 133P with submitted to the European Space Agency’s current call launch dates around 2025, and found that this, and for an M-class mission. backup MBC targets, are reachable by an ESA M-class mission. The specific science goals of the Castalia mission are: A proposal in response to the ESA M4 call for 1. Characterize a new Solar System family, the missions is currently being prepared. More details, and MBCs, by in-situ investigation an opportunity to register your support for the pro- 2. Understand the physics of activity on MBCs posal, are available at http://bit.ly/mbcmission 3. Directly sample water in the asteroid belt and test if MBCs are a viable source for Earth's water 4. Use the observed structure of an MBC as a tracer of planetary system formation and evolution.

These goals can be achieved by a spacecraft de- signed to rendezvous with and orbit an MBC for a time interval of some months, arriving before the active period for mapping and then sampling the gas and dust released during the active phase. Given the low level of activity of MBCs, and the expectation that their ac- tivity comes from only a localized patch on the sur- face, the orbiting spacecraft will have to be able to maintain a very close orbit over extended periods - the Castalia plan envisages an orbiter capable of 'hovering' autonomously at distances of only a few km from the surface of the MBC.

The strawman payload comprises a Visible and near-infrared spectral imager, Thermal infrared imager,