The Solar System Inner planets geology atmosphere

The Solar System • Inner planets; geology, atmosphere evolution • The asteroids – scrambled and fried • Outer planets and their mini-solar systems of moons • Comets: icy dirtballs or dirty iceballs?

Inner vs. Outer Planets characteristics

Temp vs distance in solar system

All planets and the sun, sizes

How Does a Planet Retain an Atmosphere? • Surface gravity must be high enough and surface temperature must be low enough that the atmosphere molecules don’t leak away during the 4. 6 billion years since formation.

Two Ways a Planet Loses Atmosphere: First… • Lighter molecules move faster, because on average Kinetic Energy = Thermal Energy • (½)m2 = (3/2)k. T • Molecules are continually bouncing off of each other and changing their speed, but if the average speed is higher, a few may be speedy enough to escape the planet’s gravity • Hydrogen and Helium = 97% of the mass of the solar nebula, and these are the lightest and easiest molecules to lose

The Second way to Lose Atmosphere… • …maybe easier to understand - Impact Cratering! Big comets and asteroids hitting the planet will deposit a lot of kinetic energy which becomes heat, blowing off a significant amount of atmosphere all at once. • This is a Big issue especially in dense areas (inner solar system), and dense times (soon after formation).

The Inner Planets • It’s hot close to the sun. No ices. So only the rocky material (~3% of the solar nebula) could collect. Not hydrogen and helium since escape velocities that are too low for these • Atmosphere histories for each planet are unique…as we’ll see

Early inner planet; a ball of lava

Inner planet interiors; summary

Mercury mariner

Mercury mud cracks

Mercury fault

Mercury • Smallest planet, only 3, 000 mi across. • 600 F on daylight side, too hot to retain any atmospheric molecules at all. Probably doesn’t help that the sun is so close and solar storms can rack the planet and help carry off any atmosphere too. • Cratering shows it hasn’t had atmosphere for most of solar system’s history

venus. HST

Venus-all

Venus lava flows

Venus-surface 1

Venus-surface 2

Venus-surface 4

Venera-left

Venera-right

Venus • Has thick CO 2 atmosphere, 100 times denser than earth’s. CO 2 is the heaviest common molecule. • Greenhouse effect – CO 2 transparent to visible light coming down from the sun, but opaque to infrared coming back off the surface, hence heat comes in but can’t easily escape. 900 K on surface!! • Let me draw you a picture…

Greenhouse effect

Earth – largest inner planet • Crust divided into tectonic plates which move due to friction against the moving molten mantle underneath. Continental drift animation • . Click here for animation website. • This likely explains why the earth has so little atmosphere. That’s one heck of an impact event.

Atmosphere; initially rich in CO 2, methane, no oxygen Why so little atmosphere, and why is CO 2 such a tiny % (~0. 3% today)? 1. Life took out CO 2 and produced O 2, and organic and inorganic processes produced Ca. CO 3. Nice! This has been lowering greenhouse gases at the same time the sun has been increasing its luminosity – balance! 2. Moon created by Mars-sized planet impacting early Earth. Evidence: (1) moon crustal age is a little younger than Earth’s, (2) moon composition = Earth mantel composition, (3) moon orbits ~in ecliptic, not equator plane as you would expect if it was formed with the earth.

Folded mountains – earth and Venus

Aurora, iceland volcano

Mt. Aetna in italy

Ozone hole

moon. Plieades

moon

Moon’s surface; maria vs highlands

Mare humorum,

Clavius 160 mi across

Apollo 15 on moon 1

Apollo 15 on moon

Graze reduction

mars. HS

Mars globe, big craters

Mars globe, w/ v. marinaris

Olympic mons caldera

Mars valle marinaris

Mars continents

Mars solis plenum

Martian sand dunes

Mars gullies

Martian surface; pathfinder

Spirit track

Mars mud cracks

Martian rock; blueberries, razorback

Mars crater edge - rover

Mars Burns. Cliffs

Mars drilling rock

Mars frozen ice floes

Mars heart-shaped crater

phobos

Phobos mars orbiter

diemos

Asteroids – Remnants of planet(s) roughed up by Jupiter? • Giant gap from Mars to Jupiter, plenty big enough to house another planet. But instead… • Thousands of bits and pieces of rock • Resonances and orbit crossings led to collisions, or maybe never came together in the first place (tidal stretching) • Total mass is less than that of Mars

The Outer Plants: Hydrogen/Helium Giants • 97% of early solar nebula was hydrogen and helium, roughly the composition of the outer planets • Cold temperatures, high mass allow these light atoms to be held by gravity for these 4. 6 billion years • Rocky cores surrounded by deep layers of H, He.

Jupiter, Saturn, Uranus, Neptune lineup

Jupiter layers

Jupiter redspots

Jupiter storms

Jupiter IR, excess heat

Jupiter + Io

Io globe

Io globe closer in

Io volcano

Io pele

Io volcano closeup

Io surface hi res

Io cutaway

Europa cracks

Europa interior cutaway

Lake Vida Antarctic

Callisto ice spires

Ganymede globe gray

Callisto globe

Callisto cratering

Jupiter small rocky moons

saturn. HST

Saturn hst 2

Saturn rings

Mimas and rings

Cassini division close up

Saturn dragon storm

Saturn aurorae

Saturn aurorae sequence

Titan haze from side

Titan color

Titan b&w oceans

Titan shorelines

titan

Titan ocean+canyon

Titan impact crater

Titan boulders. Color

phoebe

Enceladus-all

Enceladus surface wedge

Enceladus surface

Enceladus surface 2

Enceladus cracks

Mimas

Rhea cassini

iapetus. Walnut

saturn. Moon. Epithemus

Uranus, rings in ir

Uranus, rings. HST

oberon

Miranda lowres

Miranda hi res

Miranda bullseye

Miranda cliff

Neptune HST

Neptune great dark spot

triton

Beyond Neptune – cold and dark! • No planets beyond Neptune, instead, the Kuiper Belt of large comets… • “rocks” of light elements (hydrogen, oxygen, nitrogen, carbon, chlorine…) are called “ice” and melt at very low temperatures. • Globs of this stuff, mixed with plenty of dust and dirt, are called “Comets”!

Hyakutake sahuaro

Hyakutake fisheye

Hyakutake long fl lens

K 4 LINEAR

K 4 LINEAR; longer exposure

C/NEAR with SOHO

Comets – A Tale of Two Tails • Comets swing by the sun on big arcing orbits. • The gas is blown back rapidly, since gas atoms are very light. Gas tail is very straight and moves very fast – gas atoms left comet very recently. • Dust tail is yellowish and often curved, as the dust grains move very slowly, showing the history of the comets path over a longer history.

C/Machholz

C/Hale-Bopp

C/Hale-Bopp Jtree

C/Bradfield & LINEAR T 7

C/Ikeya. Zhang and M 31

Comet surface - artist

Halley closeup

C/Borrelly closeup

C/Wile closeup/ composite

Comet P 57 breaking up

S 4 LINEAR breakup b&w

S 4 LINEAR breaking up

S 4 LINEAR up close

S 4 LINEAR 4

S 4 pieces

SL 9 string of comets

Crater chain on moon

Comet Temple. Tuttle; Leonids parent

Uniform vs Leonid meteor streams

Leonids ’ 99 Ayers antiradiant

Leonids ‘ 01

Leonids ’ 01 fisheye

Leonids ’ 01 fisheye 2

Leonids ‘ 02

Leonids Jtree

Leonids ’ 02 anti radiant

Leonids ’ 02 from space

Leonids ‘ 02, lake moon

Deep. Impact

KBO’s

Sedna, quaoar, pluto, earth/moon

Asteroids – Remnants of planet(s) roughed up by Jupiter? • Giant gap from Mars to Jupiter, plenty big enough to house another planet. But instead… • Thousands of bits and pieces of rock • Resonances and orbit crossings led to collisions, or maybe never came together in the first place (tidal stretching) • Total mass is less than that of Mars

asteroid. Trails

Inner SS known asteroids all

Pallas occultation

Radar of 3. 5 km NEO

Ann. Frank from Stardust

Eros, whole thing

Eros Landing Site

Eros surface

gaspra

Ida and Dactyl to scale

Asteroid close encounters have changed some orbits, creating a population of earth-crossing asteroids. Those that haven’t already hit us, probably will in the (hopefully distant) future, Causing…. Trouble!

Daylight fireball

Michelle’s car

Fresh Russian Crater

Meteor. Crater, Arizona

Chixilub crater