The Icy 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 Can the Jovian support life?

The Moons of

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 • Strong tidal stresses and internal heating. • Density close to that of 's . • Molten silicate interior; 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

• 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 magnec 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 inera ( variaons measured by spacecra moons) • Magnec 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 + 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 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 – Densies suggest rock + ice composions – Tides can heat small bodies – Water abounds; oceans may exist

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