The Moons of the Outer Solar System AST 248 | March 27, 2017 Recap: Habitable Zone Venus

Home , Rhea (moon), Solar System

• Near the inner edge of Solar habitable zone

• Runaway greenhouse effect  too hot to be inhabitable Earth

• Just enough greenhouse effect to make it habitable

• Only planet with liquid surface water Mars

• Outside of unmodified Solar habitable zone

• Insufficient atmosphere for greenhouse effect, surface pressure too low for liquid water

• May have subsurface water ice surface Jupiter’s Galilean Moons: Io, Europa, Ganymede, Callisto

• Innermost Galilean moon

• Synchronous orbit

• Most volcanically active body

• Yellow and orange coloration from sulfur and sulfur dioxide compounds

• Has a silicate-rich crust and mantle Tides

•Tide  differential gravitational force

•Gravity ∝ 1/r2 •Tides ∝ 1/r3 Tidal Heating

Ganymede

• Largest moon in solar system

• Ice shell, rock shell, iron core

• Darker, older, cratered regions

• Mostly lighter, younger, grooved regions

Callisto

• Outermost Galilean moon

• Largest undifferentiated object in solar system  no tidal heating

• Tidally locked to Jupiter but no orbital resonance with other moons

• Very old and cratered surface of ice and rock

Europa!

• Smallest of the Galilean Moons

• Has a young smooth surface composed mostly of water ice

• Smoothest surface in the solar system

• Endures stress from gravity of Jupiter, Io, and Ganymede  high internal friction  heat melts ice  subsurface ocean • Blue regions are water ice

• Brown regions are mineral deposits

• Tidal flexing causes cracks, keeps ocean liquid, pulls minerals into water 1.6 km resolution 20 m resolution

Potential for Life

• Liquid water

• Minerals  organic chemistry

• Source of energy There is an extended habitable zone wherever:  Liquid water can be found along with  An energy source that is not necessarily What does this sunlight tell us? We can expand our search for habitable planets based on this extended definition Saturn’s Many Moons

62 known moons/moonlets Enceladus

• Sixth largest moon of Saturn

• Similar to Europa

• Icy surface, subsurface ocean

• Hydrothermal vents and geysers erupting with water, salts, and organic compounds

• Some craters, some plains  resurfacing

Tiger Stripes Plume: 2015 Cassini Flyby

Enceladus North Pole Implications for Search for Life

• Particles of silica floating near Enceladus  formed from hot water (energy source) dissolving rocky core

• Ammonia-water mixture may allow for liquid water at lower temperatures

• Further expansion of what we consider the habitable zone Saturn’s Other Moons: Rhea Mimas Iapetus Titan