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Where is this?
Where is this?
Solar System Explorers 02
1. What three ices dominate the ice giants’ composition (that is ice)?
2. What is the mass ratio of Jupiter to Saturn, 30:1, 10:1, or 3:1?
3. Which two planets do not have internally generated magnetic fields today?
4. What technique is the best for measuring the masses of the Jovian planets and
their moons?
5. Do protoplanetary disks last roughly 105, 107, or 109 years?
B. Name any moon of Uranus.
Solar System Explorers 02
Solar System Explorers 02
1. What three ices dominate the ice giants’ composition (that is ice)?
CH4, NH3, H2O
2. What is the mass ratio of Jupiter to Saturn, 30:1, 10:1, or 3:1?
3:1
3. Which two planets do not have internally generated magnetic fields today?
Venus and Mars
4. What technique is the best for measuring the masses of the Jovian planets and
their moons?
spacecraft tracking data
5. Do protoplanetary disks last roughly 105, 107, or 109 years?
107 years
B. Name any moon of Uranus.
Juliet, Portia, Puck, Miranda, Ariel, Umbriel, Titania,
Oberon …
Dynamics II
Saturn’s Rings
300,000 km wide X 10 m (!) thick
7
particles forced into plane by orbits
albedo 0.8 … shiny snowballs of H2O
Saturn’s Rings
total mass only that of small moon
young … likely formed by Roche limit crossing
8
6 major regions … 2 divisions … 1000s of ringlets
ABC rings seen from ground … major
DEFG rings seen from Voyager/Cassini … minor
Cassini Division
Encke Gap
Mimas 2:1 resonance
Pan within A ring
A ring
F ring (braided)
E ring
G ring
spokes
Atlas on edge (in 3:2 with Mimas)
shepherds Prometheus + Pandora
Enceladus volcanism (outside Roche)
Mimas drives lump of grinding dust
collisions in rings
The Saturn System
Saturn’s Rings Details
Pan
Pandora
11
Tides
tides are a differential gravitational force ~ 1 / r3
a. cause bulk motions of fluid components
ocean tides, moonquakes, Io volcanoes
2 reasons --- bulge amplitude changes, position of bulge changes
b. cause torques (~1 / r6) that lead to rotational changes
Earth day lengthening, Pluto-Charon locked,
Mercury 3:2 spin:orbit resonance
eccentric orbit…Mercury elongation…resonance
c. cause shape changes if tidal force > tensile strength/self-gravity
evidence for Moon’s shape --- closer in the past
d. likley creates rings
Tidal Forces
2 x G m2
F tidal ≈
______________
r3
r is distance between two bodies
x is distance from center of stressed body
tides on Earth
m2 (kg)
r (km)
Ftidal/2RG
Sun
1.99e30
1.50e08
5.90e05
Venus
4.87e24
4.14e07
6.86e01
Moon
7.35e22
3.84e05
1.30e06
Jupiter
1.90e27
6.29e08
7.63e00
Winner! 2.2 X Sun
Earth-Moon tidal force is 81 X Moon-Earth tidal force
Jupiter-Io tidal force is 20,000 X Moon-Earth tidal force
Tides in Earth-Moon System
angular momentum is conserved, but …
can be swapped between rotation and revolution via tidal torques
on Earth:
twice per 25 hours due to Moon
twice per 24 hours due to Sun (1/2 strength)
on Moon:
mostly fixed because of synchronous rotation
but not entirely because of eccentricity … nutation
bulge torque:
Earth rotates faster than Moon orbits
Earth not perfectly elastic, so bulge not on Earth-Moon line
Moon pulls back on bulge --- Earth slows down
Earth bulges pull on Moon --- torque acc. Moon outward ~ 1/r6
death spirals:
moons moving retrograde, or faster than planet rotates
Moon’s Shape
bulge frozen at 2/3 current Moon distance
Roche Limit
Roche limit: point beyond which an object is ripped apart by tidal forces
aRoche = 2.456 Rp (ρp/ρs)1/3
moons inside Roche limit !?!?!
Jupiter has 3 +
Saturn has ~ 0
Uranus has 8 +
Neptune has 4 +
(1) assumes fully deformable (fluid) moon
(2) assumes no “tensile strength”
… moving inward, resulting orbital systems have …
… large moons … small moons … ring particles
Roche Limits and Ring Systems
17
Neptune’s Rings
Adams
Lassell
LeVerrier
Galle
Billions of Years from Now…
Jupiter’s Rings
20
Jupiter’s Rings Details
Jupiter’s Rings Details
22
Solar System Explorers 03
Describe something you have already learned in this course that you did not know
previously.
1. clathrates are ices with molecules inserted into ice structure
2. storm on Neptune is a downwelling compared to Jupiter’s GRS upwelling
3. Titan has magic islands on its mare that appear/disappear
4. spacecraft flybys yield information about both mass and mass distribution of worlds
5. Nice Model explains
6. beta Pic disk can be seen because of double-peaked SED
7. gas giants have faster rotations than terrestrials because of conservation of angular momentum
8. Uranus and Neptune have off-center magnetic fields
9. Triton is the only LARGE moon that orbits retrograde
10. Triton was likely captured explaining why it orbits retrograde
11. a proplyd is a protoplanetary disk
12. Sun spins faster at equator than pole because convection cells push in different directions
13. Mercury spins strangely because of a 3:2 spin/orbit resonance (eccentric orbit)
14. methane makes Uranus 2% blue and Neptune 3% bluer
15. … that is why they have similar equilibrium temps
16. Centaurs exist! and are divided into active and inactive subgroups
17. it should be called the Asteroid Comb
18. Antarctica is a good place to find meteorites
19. Jupiter’s magnetotail extends to Saturn’s orbit
20. the answer to most questions is TEMPERATURE (once in awhile, GIANT IMPACT)
Solar System Explorers 04
How does the Sun affect objects in the Solar System?
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