Icy bodies: Europa and elsewhere

Introduction

Until the 1980s, the icy satellites of the outer planets were scarcely thought of as places where life could ever have existed. Few could have imagined that one of them, Europa, would within twenty years have become the rival of Mars as a priority for astrobiological study. This unit recounts the history of our changing perceptions of the icy satellites, examines the available evidence for their internal structures, and considers the niches offered for life to begin and to be sustained. In this context, the ‘habitable zone’ embraces settings devoid of both sunlight and an atmosphere. These are areas where life could survive on the energy from chemical reactions made possible by the discharge of hot chemically enriched fluids through vents on the floor of an ocean capped by a thick layer of ice. Note that ‘ice’ does not necessarily mean just frozen water. In the outer Solar System, although H₂O is usually the dominant component, ice can incorporate other frozen volatiles such as NH₃, CO₂, CO, CH₄ and N₂.

This unit is an adapted extract from the Open university course Planetary science and the search for life (S283) [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)]