Slide 1Moons of Uranus and NeptuneSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35PYTS/ASTR 206 –Moons of Uranus and Neptune1AnnouncementsHW5 due now50% credit if submitted next TuesdayPYTS/ASTR 206 –Moons of Uranus and Neptune2PTYS/ASTR 206 – The Golden Age of Planetary ExplorationShane Byrne – [email protected] of Uranus and NeptunePYTS/ASTR 206 –Moons of Uranus and Neptune3In this lecture…In this lecture…Voyager encountersRocky again?Where’s the oxygen?Moons of UranusGeologic activity on someCurious MirandaMoons (or lack of) around NeptuneTritonCapture of Triton and its effectsVoyager II – 1986, 1989PYTS/ASTR 206 –Moons of Uranus and Neptune4Launched 1977Currently at 108 and 88 AU Speed ~16 km s-1Most instruments now switched offbut there’s still one thing left to do…PYTS/ASTR 206 –Moons of Uranus and Neptune5Voyager I & II are about to become the first interstellar spacecraftThe stream of particles coming from the sun stalls at the HeliopauseVoyager I is starting to feel this, voyager II will follow soonMissions will probably end in the 2020sPYTS/ASTR 206 –Moons of Uranus and Neptune6Voyager II flyby very different in each caseUranus – Voyager passed through the equatorial planeGot a good look at only one MoonNeptune – Voyager passed along the equatorial plane Uranus 1986Neptune 1989PYTS/ASTR 206 –Moons of Uranus and Neptune7Uranian Moons small13 inner moons among the rings5 ‘mid-sized’ satellites~10 irregular, distant satellitesNamed after characters from works of Pope & ShakespeareNeptune has very few MoonsTriton is pretty large…and the reason why other moons are scarcePYTS/ASTR 206 –Moons of Uranus and Neptune8Solar system formationA disk dominated by hydrogen and heliumWarmer closer to the centerInner planets iron rich and rockyOuter planets get bulked up with water iceTransition in theasteroid beltProtoplanetary disksHubble Space TelescopePYTS/ASTR 206 –Moons of Uranus and Neptune9Jupiter forms like a mini solar systemRocky bodies close inIcy bodies further outDistance(RJ)DensityKg m-3Io 5.9 3530Europa 9.4 3020Ganymede 15 1940Callisto 26.4 1850PYTS/ASTR 206 –Moons of Uranus and Neptune10Saturn’s satellites are mostly icy Radius DensityMimas 196 km 1170 kg m-3Enceladus 250 km 1600 kg m-3Tethys 530 km 970 kg m-3Dione 560 km 1480 kg m-3Rhea 764 km 1230 kg m-3Iapetus 720 km 1034 kg m-3PYTS/ASTR 206 –Moons of Uranus and Neptune11Inner solar system All Rock Jupiter’s Moons Rock and IceSaturn’s Moons Mostly iceUranus/Neptune’s Moons ??Ganymede(Jupiter)Iapetus(Saturn)Titania(Uranus)PYTS/ASTR 206 –Moons of Uranus and Neptune12Inner solar system All Rock Jupiter’s Moons Rock and IceSaturn’s Moons Mostly iceUranus/Neptune’s Moons Less ice…. Ganymede(Jupiter)Iapetus(Saturn)Titania(Uranus)PYTS/ASTR 206 –Moons of Uranus and Neptune13Uranus satellites have more rocky stuff… not lessHow did that happen??Miranda is an exceptionTitania Ariel Oberon UmbrielDiameter 1580km 1158km 1525km 1170kmDensity 1700 kg m-31700 kg m-31600 kg m-31400 kg m-3PYTS/ASTR 206 –Moons of Uranus and Neptune14What happens to oxygen…In the inner solar system it makes rocks – Si O4At Jupiter/Saturn it makes more water ice – H2 OAt Uranus/Neptune it makes carbon monoxide – C ODecreasingTemperatureCO Freezes only at 68KCarbon monoxide ice on Pluto and comets etc…PYTS/ASTR 206 –Moons of Uranus and Neptune15The result is that satellites of Uranus (and Neptune) areSmallHave a higher proportion of rocky material than at SaturnSatellites of Uranus are 50-65% rockWarmerJupiter ~ 5AUSaturn ~10 AUCoolerUranus ~19 AUNeptune ~30 AUC CH4COO H2O CON NH3N2The same happens for various other elementsLess important than OxygenWe don’t know if they’re differentiatedNot too dissimilar from Ganymede & CallistoExcept they’re smallProbably no iron corePYTS/ASTR 206 –Moons of Uranus and Neptune16Uranus has 13 inner moonsVery dark objects, albedo < 10% (like the rings themselves)Water-ice coated with organic compounds Cordelia and Ophelia shepherd the ε ringMab is a source of Uranus's outermost μ ringRings probably generated by moon-moon collisions Moons of UranusMoons of UranusPuck – 160km acrossPYTS/ASTR 206 –Moons of Uranus and Neptune17There are five much larger ‘regular’ satellitesEncounter geometry means that only one satellite was well imagedThe south-polar region of each Moon was seen1100-1200 km1500-1600 km470kmGood pictures from VoyagerNot so good pictures from VoyagerPYTS/ASTR 206 –Moons of Uranus and Neptune18Oberon and Titania: ~1500km acrossOberonPoor imagingLarge craters visibleBright ejectaDark floor depositsTitaniaFault bounded canyonsMassive extensionShrinking surface layerExpanding coreFaults cross-cut impact cratersFewer large crater than OberonSimilar in size to Rhea at Saturn…but much more activity hereHigher silicate levels provide more heatPYTS/ASTR 206 –Moons of Uranus and Neptune19Umbriel and Ariel: ~1100km acrossUmbrielCraters are the only landformNo endogenic geology visibleVolatiles concentrated in polar regionsArielExtensive network of fault bounded canyonsCanyon floors resurfaced by viscous flowsUpbowing cross-sections with central sinuous troughsMix of surface ages implies long-lived activityTidal heating in the past ??PYTS/ASTR 206 –Moons of Uranus and Neptune20Density not size determines amount of activityHigher density caused by having more rockMore rock means more heat from radioactive elements Past tidal heating also a possibilityActive InactiveTitania Ariel Oberon UmbrielDiameter 1580km 1158km 1525km 1170kmDensity 1700 kg m-31700 kg m-31600 kg m-31400 kg m-3Albedo 0.3 0.4 0.2 0.2PYTS/ASTR 206 –Moons of Uranus and Neptune21Miranda: 472km acrossDiscovered by Kuiper, 1948Old cratered plains – uniformCoronae Tectonic disruption of surfaceInfilling with very viscous magmasPYTS/ASTR 206 –Moons of
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