The Icy Moons The Moons of Jupiter
Ganymede
ρ 1.94
Callisto
1.86
Io
3.57
The 4 Galilean moons
There are at least 59 others
Europa
2.97 g/cm3
Io
• The size of Luna
• Sulfur surface
produces the
orange, yellow, and
black colors.
Io
• The most volcanically-active body in the solar system
• Strong tidal stresses and internal heating.
• Density close to that of Earth's moon.
• Molten silicate interior; iron core
• No large craters è surface <1 million years old.
Tidal Heating
Tidal Heating on Io
Prometheus
Loki
Europa
• 2nd of the Galilean satellites
• Smoothest surface in SS
• Surface appears to be water ice
• Surface looks like Arctic Ocean
• Iceberg-like structures
• Dark lines appear to be cracks
in the ice
• No craters è < 30 million year
old surface
• Severe radiation environment
Europa
Smooth surface
- few craters
- compression ridges
- stretch fractures
Europa
Conamara Chaos - 70 x 30 km region
blue: young water ice (ejecta from crater Pwyll)
brown: mineral contaminants
Europa close-up
The surface at 1.6km resolution
Europa close-up
The surface at 230 m resolution
Europa close-up
The surface at 26 m resolution
Europa
Interior
Models
Ganymede
• 3rd of the Galilean satellites
• Bigger than Mercury
• Differentiated, iron core
• Complex surface
• dark cratered regions
• light grooved regions
• The grooved terrain:
• 60% of the surface
• Faulted
• Few craters è young
Craters Gula and Achelous Ganymede •  Only moon with a magne:c field Blue: UV Callisto
• Most distant of the
Galilean satellites
• Density è rock and ice
• Moment of inertia
èundifferentiated
• Tidal forces have not
heated its interior.
• Heavily cratered, very
old surface
Craters on Callisto Surface of Callisto Ganymede vs. Callisto Internal Structures
Internal structure Inferred from: •  Density •  Moment of iner:a (gravity varia:ons measured by spacecraH mo:ons) •  Magne:c fields Titan
The second-largest moon in the Solar System
The only moon with a substantial atmosphere
90% N2 + some CH4, Ar, C2H6, C3H8, C2H2, HCN, CO2
1.5 bars; 95K
Diameter: 5150 km (1.5 times Luna)
The Atmosphere of Titan
1.5 bar pressure, T=95 K
Condensation sequence:
• Jovian Moons: H2O ice
• Saturnian Moons: NH3, CH4
NH3, CH4 gaseous at lower temperatures
2NH3 + sunlight è N2 + 3H2
CH4 + sunlight è CH, CH2
The Intrigue
Free CH4 requires replenishment
•  Liquid methane on the surface?
Hazy atmosphere/clouds may suggest methane/
ethane precipitation.
(Liquid natural gas anyone?)
This atmosphere may resemble the early
terrestrial atmosphere.
Near-IR
image
penetrates
the haze
and sees
surface
features
Near-IR
image (933 nm)
The Sea?
Coastline?
Rivers?
Lakes and Drainage The Lake?
The Huygens Probe
Part of the Cassini mission
Landed on Titan 1/14/05
Alluvial Plains? é Panoramic view from 8 km
The surface in true color è
“Rocks” are probably water ice
The Surface
A Dynamic Surface on Titan Lessons
Titan is a dynamic world, with CH4 and C2H6 precipitation
At 8 km, the atmosphere is saturated with CH4
Surface features look like lakes and riverbeds
H2O rocks show evidence of erosion
Photochemical smog due to organic molecules
Titan has all the building blocks for life
Interior Model Enceladus
Diameter: 500 km Enceladus up close
“Tiger Stripes”
Enceladus
Tiger Stripes
IR-bright
emission
near the
south pole
of
Enceladus
Geysers
Gas and dust plumes from
occultation photometry.
V=600 km/s
March 2008
Cassini flyby
Geyser Plumes backlit
Cassini Enceladus Flyby
12 March 2008
Came within 30 km of surface
Flew through geysers at 120 km altitude
Geysers suggest
subsurface water
at 0C
Also methane
(CH4) in plumes
Enceladus Model
Ocean 10 km thick
Below 30-40 km ice
Science, 4/4/14
Images from 14 Oct 2015 Flyby: North Pole Images from 14 Oct 2015 Flyby: Craters and Fissures Images from 14 Oct 2015 Flyby: Fractures near the North Pole 28 Oct 2015 Flyby Mimas
Closest of
the large
moons.
Mimas Librates (wobbles)
6 km wobble suggests
–  a liquid interior, or
–  an oval core
See
–  http://www.sciencedaily.com/
releases/
2014/10/141016143656.htm
–  Science, 2014; 346
Lessons from the Icy Moons The large moons are unique worlds –  Densi:es suggest rock + ice composi:ons –  Tides can heat small bodies –  Water abounds; oceans may exist You do live in an interes/ng neighborhood