PYTS/ASTR 206 –Moons of Uranus and Neptune 1 Announcements HW5 due now 50% credit if submitted next TuesdayPYTS/ASTR 206 –Moons of Uranus and Neptune 2 PTYS/ASTR 206 – The Golden Age of Planetary Exploration Shane Byrne – [email protected] Moons of Uranus and NeptunePYTS/ASTR 206 –Moons of Uranus and Neptune 3 In this lecture… Voyager encounters Rocky again? Where’s the oxygen? Moons of Uranus Geologic activity on some Curious Miranda Moons (or lack of) around Neptune Triton Capture of Triton and its effects Voyager II – 1986, 1989PYTS/ASTR 206 –Moons of Uranus and Neptune 4 Launched 1977 Currently at 108 and 88 AU Speed ~16 km s-1 Most instruments now switched off but there’s still one thing left to do…PYTS/ASTR 206 –Moons of Uranus and Neptune 5 Voyager I & II are about to become the first interstellar spacecraft The stream of particles coming from the sun stalls at the Heliopause Voyager I is starting to feel this, voyager II will follow soon Missions will probably end in the 2020sPYTS/ASTR 206 –Moons of Uranus and Neptune 6 Voyager II flyby very different in each case Uranus – Voyager passed through the equatorial plane Got a good look at only one Moon Neptune – Voyager passed along the equatorial plane Uranus 1986 Neptune 1989PYTS/ASTR 206 –Moons of Uranus and Neptune 7 Uranian Moons small 13 inner moons among the rings 5 ‘mid-sized’ satellites ~10 irregular, distant satellites Named after characters from works of Pope & Shakespeare Neptune has very few Moons Triton is pretty large …and the reason why other moons are scarcePYTS/ASTR 206 –Moons of Uranus and Neptune 8 Solar system formation A disk dominated by hydrogen and helium Warmer closer to the center Inner planets iron rich and rocky Outer planets get bulked up with water ice Transition in the asteroid belt Protoplanetary disks Hubble Space TelescopePYTS/ASTR 206 –Moons of Uranus and Neptune 9 Jupiter forms like a mini solar system Rocky bodies close in Icy bodies further out Distance (RJ) Density Kg m-3 Io 5.9 3530 Europa 9.4 3020 Ganymede 15 1940 Callisto 26.4 1850PYTS/ASTR 206 –Moons of Uranus and Neptune 10 Saturn’s satellites are mostly icy Radius Density Mimas 196 km 1170 kg m-3 Enceladus 250 km 1600 kg m-3 Tethys 530 km 970 kg m-3 Dione 560 km 1480 kg m-3 Rhea 764 km 1230 kg m-3 Iapetus 720 km 1034 kg m-3PYTS/ASTR 206 –Moons of Uranus and Neptune 11 Inner solar system All Rock Jupiter’s Moons Rock and Ice Saturn’s Moons Mostly ice Uranus/Neptune’s Moons ?? Ganymede (Jupiter) Iapetus (Saturn) Titania (Uranus)PYTS/ASTR 206 –Moons of Uranus and Neptune 12 Inner solar system All Rock Jupiter’s Moons Rock and Ice Saturn’s Moons Mostly ice Uranus/Neptune’s Moons Less ice…. Ganymede (Jupiter) Iapetus (Saturn) Titania (Uranus)PYTS/ASTR 206 –Moons of Uranus and Neptune 13 Uranus satellites have more rocky stuff… not less How did that happen?? Miranda is an exception Titania Ariel Oberon Umbriel Diameter 1580km 1158km 1525km 1170km Density 1700 kg m-3 1700 kg m-3 1600 kg m-3 1400 kg m-3PYTS/ASTR 206 –Moons of Uranus and Neptune 14 What happens to oxygen… In the inner solar system it makes rocks – Si O4 At Jupiter/Saturn it makes more water ice – H2 O At Uranus/Neptune it makes carbon monoxide – C O Decreasing Temperature CO Freezes only at 68K Carbon monoxide ice on Pluto and comets etc…PYTS/ASTR 206 –Moons of Uranus and Neptune 15 The result is that satellites of Uranus (and Neptune) are Small Have a higher proportion of rocky material than at Saturn Satellites of Uranus are 50-65% rock Warmer Jupiter ~ 5AU Saturn ~10 AU Cooler Uranus ~19 AU Neptune ~30 AU C CH4 CO O H2O CO N NH3 N2 The same happens for various other elements Less important than Oxygen We don’t know if they’re differentiated Not too dissimilar from Ganymede & Callisto Except they’re small Probably no iron corePYTS/ASTR 206 –Moons of Uranus and Neptune 16 Uranus has 13 inner moons Very dark objects, albedo < 10% (like the rings themselves) Water-ice coated with organic compounds Cordelia and Ophelia shepherd the ring Mab is a source of Uranus's outermost μ ring Rings probably generated by moon-moon collisions Moons of Uranus Puck – 160km acrossPYTS/ASTR 206 –Moons of Uranus and Neptune 17 There are five much larger ‘regular’ satellites Encounter geometry means that only one satellite was well imaged The south-polar region of each Moon was seen 1100-1200 km 1500-1600 km 470km Good pictures from Voyager Not so good pictures from VoyagerPYTS/ASTR 206 –Moons of Uranus and Neptune 18 Oberon and Titania: ~1500km across Oberon Poor imaging Large craters visible Bright ejecta Dark floor deposits Titania Fault bounded canyons Massive extension Shrinking surface layer Expanding core Faults cross-cut impact craters Fewer large crater than Oberon Similar in size to Rhea at Saturn …but much more activity here Higher silicate levels provide more heatPYTS/ASTR 206 –Moons of Uranus and Neptune 19 Umbriel and Ariel: ~1100km across Umbriel Craters are the only landform No endogenic geology visible Volatiles concentrated in polar regions Ariel Extensive network of fault bounded canyons Canyon floors resurfaced by viscous flows Upbowing cross-sections with central sinuous troughs Mix of surface ages implies long-lived activity Tidal heating in the past ??PYTS/ASTR 206 –Moons of Uranus and Neptune 20 Density not size determines amount of activity Higher density caused by having more rock More rock means more heat from radioactive elements Past tidal heating also a possibility Active Inactive Titania Ariel Oberon Umbriel Diameter 1580km 1158km 1525km
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