The Icy Moons Other Worlds
• Liquid solvents are necessary for life. • Water is necessary for life as we know it. • Worlds outside the Frost Line are icy. • Temperatures can exceed equilibrium temperatures based on distance to Sun Can the Jovian planets support life?
The Moons of Jupiter
Ganymede Callisto Io Europa ρ 1.94 1.86 3.57 2.97 g/cm3
The 4 Galilean moons There are at least 75 others 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 / radiation damage Europa close-up
The surface at 1.6 km resolution Europa close-up
The surface at 230 m resolution
Europa close-up
The surface at 26 m resolution Water Plumes
Europa Interior Models
Ice shelf: • 15-25 km Ocean: • 40-100 km deep • 2-3 mes volume of Earth’s oceans Keeping Water Liquid
Water requires heat and pressure to remain stable as a liquid Europa
All these worlds are yours ... Except Europa. Attempt no landings there. Arthur C. Clarke, 2010: Odyssey Two 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 èundifferentiated
• 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 spacecra 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/propane 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 Lake
Radar penetrates clouds; measures surface roughness The Sea? Ligeia Mare Flooded Canyons
Coastline?
Rivers? River
Lakes and Drainage Alluvial Plains? The Huygens Probe
Part of the Cassini mission Landed on Titan 1/14/05
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 Subsurface Aquifers
Interior Model
Enceladus
Diameter: 500 km Enceladus Enceladus up close Enceladus “Tiger Stripes” Tiger Stripes
IR-bright emission near the south pole of Enceladus Geysers
March 2008 Cassini flyby Gas and dust plumes from occultation photometry. V=600 km/s 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