The exploration of habitable worlds with future space missions

The study of the habitable conditions in the outer solar system tends to enlarge the limits of the traditional habitable zone. Several of the icy moons show such promising conditions for the development and/or maintenance of life [1]. Jupiter’s Europa, Callisto and Ganymede as well as Saturn’s Titan and Enceladus, seem to satisfy many of the “classical” criteria for habitability such as the presence of liquid water, the energy sources to sustain metabolism and the “nutrients” over a period of time long enough to allow the development of life. Cassini-Huygens demonstrated that Titan and Enceladus possess active organic chemistries subject to seasonal variations and unique geological features [2;3]. Additionally, all these satellites show indications of harboring liquid water oceans under their icy crusts, which may even be (in the case of Europa) in direct contact with a silicate mantle floor and kept warm through time by tidally generated heat [1]. Such evidence suggests that habitability conditions can be found not only on the surfaces of Earth-like planets, but in far-away objects in their interiors. Furthermore, the strong gravitational pull caused by the giant planets may produce enough energy to sufficiently heat the cores of orbiting icy moons. Similarly, waterworlds can exist in exoplanets which are currently investigated thoroughly from large ground-based telescopes and earth observatories [1]. In the solar system, such potential habitats can be investigated with designated space missions, like ESA’s JUpiter ICy moon Explorer to Jupiter’s system (launch in 2022) [4]. Titan could be explored in the future via mission concepts like TSSM or TiMe which have been studied by the space agencies. \n \nReferences: \n \n[1] Coustenis, A., Encrenaz, Th., Cambridge Univ. Press, 2013. [2] Sohl, F., et al., in prep. [3] Solomonidou, A., et al.: PSS, DOI: 10.1016/j.pss.2012.05.003, 2013. [4] Grasset, O., et al.: PSS, in press, 2013.