HARPOON mission — Hydration And Regolith Penetration Observatory On Mars —: scientific objectives and sensor suite

Understanding the present-day behavior of water on Mars, including atmosphere–subsurface exchange processes, the possible formation of transient brines, and the stability of shallow subsurface ice, remains one of the major open questions in planetary science. HARPOON (Hydration And Regolith Penetration Observatory On Mars) is a mission concept aimed at investigating how water actively exchanges between the Martian atmosphere and subsurface, and to what extent these processes may lead to the formation of transient liquid phases under present-day Martian conditions. The mission is based on the deployment of a reduced network of penetrator-type probes [1] at different latitudes on Mars, enabling simultaneous atmospheric and subsurface measurements over diurnal and seasonal timescales. Previous presentations of the HARPOON mission focused primarily on the overall mission concept, penetrator architecture, and technical implementation [2]. The present work instead focuses on the scientific objectives of the mission, the proposed atmospheric and subsurface sensor suite, and the mission configurations required to achieve these objectives, including the evaluation of trade-offs associated with the number of probes, latitudinal deployment, measurement sampling strategies, and operational periods needed to characterize water exchange processes and potential transient brine formation on Mars.

REFERENCES:

[1] Ignacio Arruego et al., “Mars environmental networks through the MarsConnect microprobes”, EPSC Abstracts, Vol. 17, EPSC2014-92.

[2] Arruego, I., Apéstigue, V., and Toledo, D. and the MarsConnect and HARPOON teams: HARPOON mission concept: Hydration And Regolith Penetration Observatory On Mars, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–12 Sep 2025, EPSC-DPS2025-1604, https://doi.org/10.5194/epsc-dps2025-1604, 2025.