| Today: Extra Credit Articles | |
| Ch. 18, Jovian Planets | |
| Recall: Nice webpage your classmate provided http://www.nationalgeographic.com/solarsystem/splash.html | |
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) | |||
Ice+Rock Core H+He “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 Ž clouds | |
| Colors from unknown trace chemicals | |
| Density of gas smoothly increases with
depth till point where it is indistinguishable from liquid Ž no real “surface” |
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| At very high temperatures and pressures
hydrogen becomes a “metal” and conducts electricity Ž generates magnetic field |
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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 Ž clouds | |
| Colors from unknown trace chemicals | |
Magnetic fields and trapped particles
| 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 | ||||
Effects of T (and E) on Atmospheres
| Saturn’s bands much less distinct than Jupiter’s | |||
| Temp. lower on Saturn Ž cloud condense lower | |||
| Deeper clouds Ž markings less visible | |||
| Differences at Uranus and Neptune | |||
| Even colder Ž 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 |
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| 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 |
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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 |
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| 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 |
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| 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 | |||
Saturn as seen by the Hubble Space Telescope
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 |
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| 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 |
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| 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 | |||
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 |
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| 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 |
| All within Roche limit | |
| Details controlled by Resonances and Shepard Satellites |
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 | ||
Io, Europa break rules about activity
| Io most volcanically active body in solar system | |
| Europa shows new icy surface with few craters |
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 |
| 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 |
| 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 Ž 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 | ||
| 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 | ||