Life in the outer Solar System AST 309 part 2: Extraterrestrial Life
Prospects for life on: Overview: 1. Europa (Jupiter moon) 2. Titan (Saturn s moon) 3. Enceladus (Saturn s moon)
Life on Europa? Europa is the sixth of Jupiter's known satellites and the fourth largest; it is the second of the Galilean moons. Europa is slightly smaller than the Earth's Moon. Galileo Galilei Europa 1610!
Life on Europa? Spacecraft exploring the Galilean satellites: Voyager 1 & 2 Galileo
Life on Europa? Basic Properties of Europa: Semimajor axis = 671079 km Orbital period = 3.551810 days Heliocentric Distance = 5.203 AU Rotational Period Synchronous Orbital inclination = 0.464 degrees Eccentricity = 0.0101 Radius = 1565 km Mass = 4.797E22 kg Mean density = 2.99 g/cm3 Surface Gravity = 0.135 of Earth's Escape Velocity = 2.02 km/s Geometric Albedo = 0.6 Surface Temperature = 128 K (-145 C) Surface Composition = Water Ice Tenuous O2 Atmosphere = Surface Pressure about 10-11 Earth's
Europa s surface is smooth and young (no craters), and is covered with cracks: Europa is tidally heated like Io (just less) and has maybe the youngest surface in the outer solar system! Icebergs on the surface moved by liquid water that later froze or by slushy warmer ice beneath?
Europa is heated by tidal forces from nearby massive Jupiter and has forced orbital eccentricity of 0.0094 from the gravitational interactions with the other Galilean moons: That is exactly the same process that drives Io s intensive volcanism: Europa is tidally heated like Io (just less) and has maybe the youngest surface in the outer solar system!
2 models of Europa s interior: Artist s conception of the surface of Europa
Cycloidal features ( flexi ) near Europa s south pole. These cycloidal cracks form in Europa's solid-ice surface with the daily rise and fall of tides in the subsurface ocean (Gregory V. Hoppa, Randall Tufts, Richard Greenberg and Paul Geissler of the Luna and Planetary Laboratory, University of Arizona). This image shows what appears to be the most convincing evidence yet for a global ocean under Europa's icy crust.
Reasons why Europa is so interesting: the likely presence of a sub-surface ocean of liquid water (perhaps as much as 150 km deep) which could provide a medium and solvent for life. intense radiation from Jupiter's magnetosphere striking ice on Europa's surface and releasing oxygen, which if it finds its way into ocean could provide a fuel for life; the possible presence of undersea volcanic vents, which could furnish energy and nutrients for organisms.
Reasons why Europa is so interesting: Chaotic features seen in many images of Europa's icy surface are probably created by Europa's tides, and are believed to be evidence of melt-through needed for exposing the oceans. The mixing of substances needed to support primative life may be driven by the tides on Europa, with maximum heights of 500 meters (much larger than Earth tides). Circulation of liquid water through cracks produced by tidal forces could bring salts and organic compounds dissolved in the water up to Europa's surface. This circulation also brings biologically useful chemicals, such as formaldehyde (as well as organic compounds dumped on Europa's surface by cometary impacts) down to the subsurface ocean. Other chemicals, formed by radiation near the surface, such as sulfur, hydrogen peroxide, and free oxygen, would also provide primative life with sources of energy and nutrients. Hydrothermal vents would produce organic compounds (seen as dark material coloring cracks?) and provide a heat source. Undersea volcanism could also lead to large melt-throughs, and tidal heat, created by internal friction could also melt the ice. The melted-through ice provides light and surface chemicals to the oceans. Any creatures inhabiting these oceans could use photosynthesis for energy.
The question really is: is the ice thin or thick? Tides and undersea volcanoes could play a role too!
Let s go there and find out! Before we drill, we would send a radar mapping probe to measure the thickness of the ice crust! Indirect evidence from large craters suggest a thickness of 19 to 25 km. On Europa, larger craters become smoothed out with gentle concentric rings. They are shallower than their counterparts on other moons. This is because of the influence of a very thick cushion of ice (Schenk, 2002, Nature)