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 magneMc 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 inerMa (gravity variaons measured by spacecra moMons) • MagneMc 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 – DensiMes suggest rock + ice composiMons – Tides can heat small bodies – Water abounds; oceans may exist You do live in an interesng neighborhood .