Chapter 17 - Hunting for environments favorable to life on planets, moons, dwarf planets, and meteorites

Abstract

“Life as we know it” is carbon-based life that uses water as a solvent. Water, biologically important chemical elements, and energy are required to sustain life as we know it. A careful examination of the presence of extraterrestrial water, oceans & seas, lakes, and rivers indicates that starting from Earth’s closest neighbor (Earth’s Moon) to its most distant dwarf planet Pluto, which orbits in the outer periphery of the Solar System, there are many celestial bodies in the Solar System that possess copious quantities of water in one form or the other (e.g., hydrated minerals, water vapor, liquid water, solid water-ice) either on the surface or below surface. For example, Earth’s Moon possesses hydrated minerals and various forms of water. Free from harmful radiation and having pleasant temperature, subsurface empty lava tube complexes and caves on this Moon are potential shelters for human settlement. Large and small subsurface liquid water lakes and water-ice deposits are available on Mars. Hydrated sulfates on Martian surface has a biological implication. There are indications suggestive of Mars’ subsurface harboring a vast microbial biosphere. Immediately beyond Mars, there exists an asteroid Ceres in the asteroid belt, which possesses water. The dwarf planet Ceres is a “candidate ocean world” in the asteroid belt. The inferred possibility of hydrothermal geochemistry to take place on Ceres could be an indication of the prospects of microbial life on Ceres. Moving further away from Earth, Jupiter’s icy moons Europa, Ganymede, and Callisto and Saturn’s moons Enceladus and Titan possess oceans hiding below their surface. Mineral- and organic-rich water vapor plumes spewing from some locations on Europa and Enceladus are testimony to the existence of hydrothermal vents on their seafloors, akin to terrestrial submarine hydrothermal vents, which are abode of single- and multi-cellular life-forms. Hydrocarbon (ethane and methane) seas and lakes on the surface of Titan, and the likely transient liquid water environments on its surface are reminiscent of similar environments on the prebiotic early Earth. Moving further away from Earth, Neptune’s moon Triton is considered to be the highest priority “candidate ocean world.” Dust devils-like tall plumes of gas and dark material rising through Triton’s atmosphere throws hope of a Triton biosphere. Finally, a subsurface ocean exists even on Pluto, which is the farthest celestial body in the Solar System. Astrobiologists think that Pluto’s primarily reddish-colored complex organic molecules-rich surface as well as a subsurface ocean might be ripe for the existence of life.