Chapter 10 - Liquid water lake under ice in Mars’s southern hemisphere—Possibility of subsurface biosphere and life

Abstract

The search for traces of life is one of the principal objectives of Mars exploration. Central to this objective is the concept of habitability, the set of conditions that allows the appearance of life and successful establishment of micro-organisms in any one location. This chapter begins with a discussion on Mars’ glorious past; how this red planet was once water-rich, whose surface dried later; and its favorable position in Sun’s habitable zone. The topics next addressed are water-bearing minerals on Mars, its hydrologic history, its potential for hosting life; evidence for hydrated sulfates on its surface and the biological implications in terms of its potential for plant growth; day–night variations in liquid interfacial water in its surface; and clues leading to the existence of water at its subsurface. Discussed next are searching for presence of liquid water at the base of the Martian Polar caps using ground-penetrating radar deployed on Mars Express spacecraft and the year-2018 path-breaking discovery of an underground liquid water lake in Mars’ southern hemisphere. Presence of liquid water lake under ice raises possibility of subsurface biosphere and life on Mars. The topics next addressed are related to Mars’ potential for possible life and habitability, such as indications suggestive of Mars’ subsurface harboring a vast microbial biosphere; search for biosignatures and habitability on early Mars with the support of European Space Agency’s and the Russian Space Agency Roscosmos’ ExoMars Rover; and search for life on Mars under NASA’s Phoenix mission and NASA’s biology experiments. The topics next discussed are discovery of volcanoes, lava plains, giant canyons, craters, wind-formed features, and seasonal dust storms under United States’ Viking lander missions 1 and 2, and search for signs of primitive life on Mars. Another two important topics addressed are Mars’s exploration under Rover mission to assess past environmental conditions for suitability for life. Next discussed are exploration of Mars’ surface features, morphology, mineralogy, atmosphere, its dynamical events, and its moons Phobos and Deimos; solar forcing on its atmosphere and exosphere, emission of thermal infrared radiation, and D/H ratio estimation of its atmosphere/exosphere through India’s Mars Orbiter Mission (MOM). The topics next addressed in terms of habitability considerations are detection of methane, ultraviolet radiation, perchlorates, and hydrogen peroxide in its atmosphere and their biological implications. Search for organic substances in the Martian soil and the possibility of plants growth on Mars are addressed next, together with an optimistic note on the possibility of halophilic life on Mars as well as the global initiative for permanent human settlement on Mars. Finally, UAE’s Hope and China’s Tianwen-1 missions to Mars are discussed, highlighting the science goals of both these year-2021 success stories.