Lecture 17. Solar System Debris
A. Class Business
- Late Night Planet Viewing?
- Reading for Wednesday -- Ch. 14, Ch. 15
- Write Ups
B. Satellites & Rings
- Moons
- most orbit CCW (counterclockwise)
from NCP (North Celestial Pole) -- error in text?
- two Jovian moons of note:
- Europa -- seas of water ice beneath
frozen surface? (life?)
- Io -- volcanically active;
due to Jupiter's tidal forces
- Rings
- Formation
- moon(s) break up -- tidal forces
- moon(s) never even formed!
- small moon(s) formed, but broken up in collision(s)
- almost all are within tidal stability limit (fig. 11.15)
-- no large moons there
- Structure --
clumpiness due to satellites*
C. Debris
- Comets
- "DIRTY SNOWBALL" is accepted model
- we know there's "snow"
-- water ice (dry ice, CO2, and CO, too)
- Q: what's the "dirt"?
-- satellites say it's "dirt": hydrocarbons
- nucleus a few km across
- Sun "bakes" gas off, resulting in huge cloud
- The Comets Three Fates:
- Chewed Up -- fragments and/or hits planet,
a la Shoemaker-Levy 9
- Spit Out --
knocked out of closed orbit, never returns
- Toyed With -- in ever-decaying orbit
'til it boils away, fragments, or hits something
(see 1.) -- 1000 passes tops
-
A Tale of Two Tails* -- point in different directions
- ION (charged!) tail flows away from Sun,
along direction of solar wind
- DUST tail is debris left along orbital path;
follows Keplerian orbital path
- Comets' Origins -- two main sources
- Oort Cloud -- from 50,000 AU, 10 trillion,
primordial: have been in deep freeze since beginning
- Kuiper Belt -- 50 AU
- Stones from the Sky
- METEORS in the sky,
METEORITES on the ground
- FALLS (tracked) vs. FINDS (serendipity)
- most meteors are small -- pea sized, 1 g
- meteor showers = enhancement of meteor frequency
- comets' debris fuels -- new passes recharge
- named for constellation of radiant
- Compostion -- meteorites are STONES or IRONS
- DIFFERENTIATED or PRIMORDIAL
- carbonaceus -- complex molecules: amino acids
D. Solar System Formation
- CONSTRAINTS
- it's all the same age!
- meteorites are all 4.5 billion years old
- Moon's are also 4.5 byr
- Earth rocks are 3.8 byr -- but volcanism alters
- COMPOSITION -- TRIP's vs. GG's (Lecture 15)
- DYNAMICS -- sense of rotation,
primarily CCW from NCP (Lecture 15)
-
Three Theories*:
- haphazard accumulation -- chance captures of planets/planetesimals
- catastrophic origin -- another star collides with Sun,
gas dragged off forms Jupiter, etc.
- SOLAR NEBULA -- accepted theory
- initially, a gas cloud
- gravity causes cloud to collapse
- conservation of angular momentum causes
material to orbit
- slowly first, then faster with more contraction
- (like spinning of draining water)
- gravity flattens along axis of rotation
- planetesimals ACCRETE
-- accumulate matter by gravitational attraction
- VOILA! spins all match, material the same, and same age, etc.
- for images, check out this
great web page!*