Lecture 5: Overview of the Icy Moons, Comets, & Kuiper Belt ObjectsAstro 202Prof. Jim Bell ([email protected])Spring 2008But first...You should be doing research for Paper 2Identify your topic of interestIdentify reliable, authoritative sourcesConduct interviews (email, in person)Paper 2 due at beginning of class on Feb. 14Don’t wait until the last minute!Graded Paper 1 will be handed back ThursdayAstro 202 3Icy Moons, Comets, and KBOs!!Io, Europa, Ganymede, & Callisto!Titan and Triton!...and many smaller worlds!Comets!Pluto and the Kuiper BeltAstro 2024Moons!!Jupiter–4 large "Galilean satellites"•Io, Europa, Ganymede, Callisto–59 other smaller satellites!Saturn–Titan: large moon with a thick atmosphere–6 medium, and 53 smaller satellites!Uranus–5 medium, 22 smaller satellites!Neptune–Triton: large moon with a thin atmosphere–12 other smaller satellitesAstro 2025Major Properties• Distinct and important differences in density, composition, and orbital properties • Io has volcanoes!• Europa has an ocean?• Titan has a thick atmosphere! Surface details unknown...• Triton has a thin atmosphere (very similar to Pluto?)• Many other small icy satellites59532212Astro 2026Relative sizes of the major satellites and small planetsSizes (not distances) to scaleAstro 2027Major Satellites of Jupiter!New worlds discovered by Galileo in 1610!A "mini solar system"... by Jove!!Io– Active volcanoes!!Europa– Subsurface ocean?!Ganymede– Large-scale tectonism!Callisto– Battered surfaceIoEuropaGanymedeCallistoGalilean Satellite Interior ModelsAstro 2029Io ("EYE-oh")!Inner Galilean moon!Most volcanically-active world in the solar system!!Interior melted by tides from Jupiter & other moonsDensity: 3.57 g/cm3Eccentricity not exactly 0Tidal energy heats the interior!Astro 20210Io's Amazing Landforms!• Volcanic calderas several km deep• Lakes of molten sulfur• Some mountains that are not volcanoes • Lava flows hundreds of km longLow viscosity fluid (sulfur rich?)Flow temperatures > 1000°C to 1500°C• Volcanic vents• Io's color caused by sulfur compoundsVolcanism on Io:Extensive lava flowsNo impact cratersColors consistentwith molten sufur at different Temps.(up to ~2000 K)Astro 20212Europa• Ice-covered Moon• flat flat flat!• Crust broken up into moving plates!• "salty" deposits well up between plates• Subsurface ocean?? Map of salt-rich "contaminants" in Europa's crust• Ridges show different compositions: hydrated sulfate salts that appear to have “erupted” from the interior (ocean?)...Ganymede• Largest moon in solar system• Complex grooved, cratered surfaceAstro 20215Ganymede• Icy surface with bright & dark areas• Many more craters than Europa (older)• But craters degraded or "softened"• Extensive network of tectonic ridges“Palimpsests”(ghost craters)• Evidence for icy/viscous relaxation?Cross-cutting grooves, furrows; evidence of tectonic folding, stretchingAstro 20217Callisto• Ancient, heavily cratered surface• Bright icy deposits• Dark "powdery" coating of unknown compositionCallisto• Why no active geology?• Why is surface “powdery”?Smaller Jovian Moons...From left to right, Galileo spacecraft images of Metis (longest dimension is approximately 60 kilometers or 37 miles across), Adrastea (20 kilometers or 12 miles across), Amalthea (247 kilometers or 154 miles across), and Thebe (116 kilometers or 72 miles across). Distance Radius Satellite (000 km) (km) Disc.--------- -------- ------ -----Metis 128 20 1979Adrastea 129 10 1979Amalthea 181 98 1892Thebe 222 50 1979Io 422 1815 1610Europa 671 1569 1610Ganymede 1070 2631 1610Callisto 1883 2400 1610Leda 11094 8 1974Himalia 11480 93 1904Lysithea 11720 18 1938Elara 11737 38 1905Ananke 21200 15 1951Carme 22600 20 1938Pasiphae 23500 25 1908Sinope 23700 18 191447 tiny outer moons found in the last decade...More probably still to be found!Are these captured asteroids?http://www.dtm.ciw.edu/sheppard/satellites/Astro 20220Major Satellites of Saturn!Titan– Larger than Mercury!– Thick atmosphere!!6 mid-size moons– All icy– All heavily cratered– But different crater densities, implying unique resurfacing historiesAstro 202Titan• Mercury-sized “planet”!• Thick, hazy atmosphere, with lots of hydrocarbons! - formed by sunlight breaking up CH4 molecules - similar to early Earth?• Surface pressure: 1.5 bars!• Surface temp.: 95K (-290°F)• Cassini/Huygens lander: 2005HSTInfraredVoyager 2- Infrared, Radar Mapping- Huygens descent imaging and landerView during descent,and from the surfaceAstro 20224Mid-sized icy Saturnian moons...Enceladus• Only 500 km diameter, yet internally active!• Subsurface liquid water? Newest astrobiology “hotspot” in the solar system...?Satellites of UranusAstro 20229Major Satellites of Uranus!5 mid-size moons!All icy!All fairly dark [why?]!All heavily cratered– But: Evidence for resurfacing, tectonism, and other processesMiranda Ariel Umbriel Titania OberonAstro 20230Miranda• Tiny moon (< 500 km diameter)• Yet some of the strangest and least understood geology in the solar system!• Recall that out here, ice acts like rock20 km cliff!Ariel (above), Titania (left): Extensional Graben?Heavily cratered Umbriel (top right) and Oberon (right)Neptune’s large moon Triton:N2 ice, few craters, exotic terrains, active geologyAstro 202Triton: Neptune's only large satellite!Nearly same size and density as Pluto–Triton: R = 1350 km; ! = 2.08 g/cm3–Pluto: R = 1140 km; ! = 2.07 g/cm3!Bizarre backwards orbit and high tilt– is Triton a "captured Pluto"?!Surface is bright: albedo = 0.7 to 0.8!Surface T only ! 35K (-391°F)!Thin atmosphere! P = 0.01 mbar!Few craters: Surface is "young"!Voyager discovered active geysers!– “volcanoes” of ice and other volatiles“Lakes” “cantaloupe terrain” and ice volcanoes on TritonAstro 20235Small satellitesof SaturnProteus (Neptune)Outer Uranian moonInner satellites of JupiterMinor SatellitesAstro 20236Comets!Comets are small icy objects from the outer solar system that evaporate spectacularly as they get heated when their orbits carry them closer to the Sun•Where do