Chapter 11- Moons and Rings Flashcards
How were the moons formed?
Many of the larger moons formed in nebulae around the planets.
Many of the smaller moons are chunks of rock and are likely captured asteroids, except for Triton and Nereid. These were likely captured by Neptune and are quite large.
Ganymede (Jupiter)
Largest moon in the solar system.
Many ices in the planetesimals which accreted to form it; contains much water.
Large magnetic field (water and dissolved minerals are conductors) which is partially produced by Ganymede and induced by Jupiter’s magnetic field.
Europa (Jupiter)
Europa is close enough to Jupiter to experience tidal flexing, and this probably keeps its water interior liquid. This flexing apparently produces tectonic activity which has obliterated older craters and pushed ice rafts around on the surface. There is also a magnetic field similar to Ganymede’s.
Callisto (Jupiter)
The farthest of the major moons of Jupiter. It, too, has a magnetic field so there are suspicions of liquid water beneath the surface. All four of the Galilean satellites are tidal locked to Jupiter.
Io (Jupiter)
Extreme tidal flexing caused by its nearness to Jupiter. It is the most geologically active world in the solar system with volcanoes erupting all the time.
Triton (Neptune)
Orbit is inclined considerably to Neptune’s orbital plane.
Orbit is unstable because the equatorial bulge (caused by Neptune’s rapid rotation) exerts a gravitational pull which will eventually realign the orbit with Neptune’s equator.
The fact that this has not yet happened suggests that Triton has only been around Neptune for a few hundred million years and is thus a captured asteroid.
Triton (continued)
Triton’s orbit is also retrograde, and this, too, is unstable.
The tidal bulges raised on the surface of Neptune (not the same thing as the equatorial bulge) pull Triton back in its orbit and slow it down. Thus it loses energy and will eventually spiral toward Neptune. When it crosses the Roche Limit it will be torn asunder and become part of Neptune’s ring system.
Neireid (Neptune)
Nereid, the third largest of Neptune’s dozen or so satellites, is in a prograde orbit.
Orbit has the largest eccentricity of any satellite in the solar system. Thus it, too, is probably a captured asteroid.
Titan (Neptune)
This is the one satellite (other than our own) we have actually landed upon.
Thick atmosphere with nitrogen, ammonia, methane and other hydrocarbons. The abundance of ammonia suggests that it is being renewed by active volcanoes.
Overall, the results suggest a hydrological cycle on Titan (with liquid hydrocarbons) very similar to the hydrological cycle (with water) on Earth.
Enceladus (Saturn)
Enceladus is geologically active, perhaps because of tidal flexing from Saturn. It produces ice geysers, which, because of the satellite’s small gravity, send particles out into space. These seem to be primarily responsible for Saturn’s E Ring.
Mimas (Saturn)
Mimas is closer to Saturn than is Enceladus, and so it, too, should be geologically active. But it doesn’t appear to be. Not clear why not.
Hyperion (Saturn)
This satellite has a strange texture (see Fig 11-3) and a low density. It is also tumbling and rotating chaotically.
Iapetus (Saturn)
Iapetus is tidal locked to Saturn, so it always faces Saturn. This means that it always has the same leading side and the same trailing side in its orbit. The leading side has become darkened by plowing through the debris of space. The leading edge has an albedo of 0.05 while the trailing edge has an albedo of 0.50.
Rings of Saturn
Discovered by Galileo in early 1600’s, not resolved clearly as rings until half a century later.
Rings disappeared for a few years because they are tilted slightly with respect to the ecliptic.
Each ring particle is in it’s own orbit, governed by Kepler’s Third Law.
Shepherd satellites
Pandora (outside) and Prometheus (inside) confine the particles of Saturn’s F Ring.
Kepler’s third law- farther a particle is from Saturn, longer it’s period and the more slowly it moves. Kinetic energy decreases as you move outward; while the potential energy increases. Total energy increases as you move outward.
If a particle in the F Ring moves outward, Prometheus will slow it down and cause it to drift back inward. If it drifts toward Prometheus it will speed up and drift back outward. This feedback mechanism keeps the particles confined.
