Life in The Outer Solar System

AST 309
part 2:
Extraterrestrial Life
Life in the outer Solar System

Overview:
Prospects for life on:
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:
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 Icebergs on the surface moved
the outer solar system! by liquid water that later froze or
by slushy warmer ice beneath?
Europa:
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!
Europa:
2 models of Europa’s
interior:
Artist’s conception of the surface

of Europa
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.
Europa:
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.
Europa:
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!
Europa:
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)

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AST 309

Life in the outer Solar System

Prospects for life on:

1. Europa (Jupiter moon)

• Spacecraft exploring the Galilean satellites:

Basic Properties of Europa:

Semimajor axis = 671079 km

Europa is tidally heated like Io (just less)

That is exactly the same process

Europa is tidally heated like Io (just less)

Artist’s conception of the surface

• the likely presence of a sub-surface ocean of liquid water

• intense radiation from Jupiter's magnetosphere striking ice

• the possible presence of undersea volcanic vents, which

Let’s go there and find out!

Before we drill, we would

Indirect evidence from large craters suggest a

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