Lecture 15. C. Planets, one at a time...
(I won't review properties discussed before under categories of terrestial/rocky/inner planets -- TRIP's, or gas giant/outer planets -- GG's
0. the Moon
- formation --
- i) fission -- split from Earth; but why not more like Earth?
- ii) sister = simultaneous formation; but why difference?
- iii) capture; then why similarity?
- iv) giant impact = some terrestrial, some "E.T." -- best!
- one face toward us = "tidally locked"
Why? more dark mare ("seas") this side = maybe inhomogenous interior
- stabilizes Earth's rotation, allows us to evolve? if so, we're lucky!
- only E.T. body visited by humans
1. Mercury
- Mercury's day = 2/3 Mercury's year -- from Doppler radar measurements!
- FYI: orbit doesn't close = "precesses"
- spiralgraph like
- explained by Einstein -- more later!
- one of two without moon!
- TRIP
2. Venus
- cloudy & hot -- "runaway" greenhouse effect? Earth's fate?
- volcanically active
- backward rotation (also from radar Doppler shift) -- collision caused?
- the other of two without moon
- brightest at Earth: very bright in W now at sunset -- "Evening Star"
- TRIP
3. Earth
- Greenhouse gasses trap heat -- NOT same as
OZONE HOLE* problem!
- Dinosaurs taken out by comet?
- layer of "space dust" -- meteoritic abundance of elements (iridium)
- crater near Yucatan -- variations in gravity there = crust different
- it can happen! -- comet Shoemaker-Levy hit Jupiter;
comet above Tunguska, Siberia
- TRIP
4. Mars
- has water and CO2 ice now
- maybe had regularly flowing water in past -- evidence of erosion;
but water could be ice melted by impacts
- no magnetic field -- less protection from Sun's solar wind! (more later)
- up in SW at Sunset
- TRIP
5. Jupiter
- largest
- most massive -- has by far biggest mass other than Sun
- usu. next brightest planet -- rising late now
- GG
6. Saturn
- famous rings -- more Monday!
- rising late now
- GGOP
7. Uranus
- funny rotation -- its pole points sideways!
- long seasons! (20+ Earth years!)
- collision caused?
- is up now, but faint -- best chance to see tonight!
- GG
- unlike other 3 GG's, has no internal heat source
8. Neptune
- is up now, but faint -- best chance to see tonight!
- GG
9. Pluto
- as discussed above, is an oddball!
- is out, but quite faint, and only a speck if seen with telescope; Uranus and Neptune have more color