1	Astr 1050 Wed., Dec. 11, 2002 Today: Course Evaluations Chapter 18, Jovian Planets
2	Chapter 18: Worlds of the Outer Solar System Jupiter Condensation model Atmospheric winds Atmospheric chemistry Magnetic fields Other Jovian Planets (Saturn, Uranus, Neptune) will only cover major differences from Jupiter Satellites (i.e. Moons)
3	Jovian Planets
4	Ice+Rock Core H+He “Atmosphere”
5	Details of the atmosphere Mostly made of H, He Trace amounts of C, N, O, S CH₄ present as gas NH₃, NH₄SH, H₂O can condense in colder upper regions Þ clouds Colors from unknown trace chemicals Density of gas smoothly increases with depth till point where it is indistinguishable from liquid Þ no real “surface” At very high temperatures and pressures hydrogen becomes a “metal” and conducts electricity Þ generates magnetic field
6	Jupiter as seen by Cassini
7	Winds on Jupiter
8	Jupiter-Cassini Movie Mercator Projection
9	Winds near the Great Red Spot
10	Air circulation for very slowly rotating planet
11
12
13
14
15
16	Hurricanes exist because Low Pressure trying to turn winds to the left almost balance Coriolis Force trying to turn winds to the right.
17	Comparison of atmospheres
18	Jupiter has multiple cloud decks as air rises in low pressure “zones” Mostly made of H, He Trace amounts of C, N, O, S CH₄ present as gas NH₃, NH₄SH, H₂O can condense in colder upper regions Þ clouds Colors from unknown trace chemicals
19	Magnetic fields and trapped particles
20	Satellites orbiting through radiation belts lose particles which become ionized and trapped.
21	Aurora on Jupiter
22	Jovian Planets
23	Comparison of Jovian Planets Variation in distance presumably ultimate causes other effects P: Kepler’s third law T: Falloff mostly just result of falling solar energy But Neptune hotter because more internal heat M: Clue to details of solar nebula mode Less material in outer solar system – or perhaps less efficient capture r: Should drop with mass because less compression Works for Saturn vs. Jupiter Increase for Uranus, Neptune indicates less H, He and more heavy material
24	Effects of T (and E) on Atmospheres Saturn’s bands much less distinct than Jupiter’s Temp. lower on Saturn Þ cloud condense lower Deeper clouds Þ markings less visible Differences at Uranus and Neptune Even colder Þ clouds even deeper So cold CH₄ can condense Little solar energy to drive weather Uranus has strange seasons – tipped on its side Neptune has strong internal heat source, so it still can have weather Large amounts of heavy elements compared to amount of H, He on Jupiter, Saturn Large amounts of CH₄ gas absorb red, make planets appear blue
25	Implications of M, r for nebula Relative amount of H, He (compared to heavy elements) drop for Saturn then drop dramatically at Uranus and Neptune Why were these outer planets so less efficient at capturing H, He? Their mass is still great enough to do this, especially given low temperatures in the outer solar system May be a problem of timing Accretion takes longer in the outer solar system because The velocities of all objects there are much less The distances between objects are greater This is the same reason the periods of the orbits are so long Uranus and Neptune may have only started to grow to critical size by the time the H, He gas was being driven out of the solar system
26	The Jovian planets are miniature solar systems Because planets captured gas as they were forming they had small “solar” nebulae Þ tests of nebula theory Regular satellite systems Large moons in direct (i.e. counterclockwise), equatorial orbits Preserve solid material from time of formation Jupiter shows solar-system like density gradients Rings Moons unusual and interesting objects in their own right Io – most volcanically active body in solar system Europa – may have liquid water ocean (and life!) Titan – only satellite with a thick atmosphere Many properties are due to tidal forces and resonances
27	The Roche Limit When can tides tear a moon apart? As a planetary body get close to another object, tidal forces distort the body more and more. Remember, Earth raises tides on the Moon just like it raises tides on the Earth If the distortion gets large enough, the moon will be pulled apart Happens at “Roche Limit” when moon is ~2.44 ´ radius of planet away At that point, tidal force pulling up on surface of moon is greater than moon’s gravity pulling down Only matters for objects held together by gravity Astronaut in orbit will not be pulled apart Is held together by much stronger chemical forces Astronaut standing on the outside of the shuttle, hoping the shuttle’s gravity would hold her there, will be pulled away from the shuttle
28	Saturn as seen by the Hubble Space Telescope
29	Rings are individual particles all orbiting separately Each particle – dust to golf ball to boulder size – is really a separate moon on its own orbit Orbit with Keplerian velocities: high in close, slow farther out Nearby relative velocities are low – so particles just gently bump into each other – slowly grinding themselves up Structure in rings largely caused by gravity of moons
30	Resonances: Properly timed gravitational “pushes” Like someone pushing kid on a swing Timing of pushes just as important as force used Pushing at random times has little effect Pushing at just right point in each cycle can produce big effect
31	Cassini division at 1:2 resonance with Mimas
32	Comparison of Rings All within Roche limit Details controlled by Resonances and Shepard Satellites
33	Jupiter as a miniature solar system Four large moons (Io, Europa, Ganymede, Callisto) Regular (equatorial, circular) orbits Pattern of changing density and composition with distance Inner two (Io, Europa) mostly rocky Outer two (Ganymede, Callisto) more icy
34	Io, Europa break rules about activity Io most volcanically active body in solar system Europa shows new icy surface with few craters
35	Tidal heating explains activity Large tides from Jupiter flex satellites Friction from flexing heats interiors Important for Io, Europa, some other outer solar system satellites
36	Possible H₂O ocean on Europa Tidal heating may keep H₂O liquid under ice cover Perhaps a location where life could evolve “Europa Orbiter” Mission being planned to determine if ocean exists
37	Callisto not active
38	Comparison of Satellites
39	Titan Largest moon of Saturn Has thick atmosphere Pressure ~ 1 earth atmosphere Mostly N₂, some CH₄ Gas held because of low T UV acting on CH₄ Þ smog Ethane produced – Lakes? Can “see” surface only in IR Cassini will drop probe in Fall 2004 “Code of the Lifemaker” by James P. Hogan, good sf
40	Triton Largest moon of Neptune In unusual retrograde orbit Probably captured after it formed Tides during capture may have caused heating Does have thin atmosphere Shows recent “activity” Not volcanic – rather volatile related Ices migrate with seasons “Geysers” caused by heated ices