Astr 1050 Fri., Dec. 9, 2005

Today: Solar System Overview

Solar System topics for the exam:

General properties of the planets

Order, relative size, make-up (terrestrial vs. Jovian), atmosphere (including greenhouse effect)

General properties of the interesting moons and ring systems (e.g., origin of our moon, Galilean Moons, Titan)

Extrasolar planets (how many, how detected?)

Comets, meteors, asteroids

Where do they come from, what are they made of, origin of meteor showers

Very basic stuff, most can be memorized, nothing too complex – basically what’s here in the slides

Chapter 16: Origin of the Solar System

Solar Nebula Hypothesis

Context for Understanding Solar System

Extrasolar Planets

Dust Disks, Doppler Shifts, Transits and Eclipses

Survey of the Solar System

Terrestrial Planets

Jovian Planets

Other “Stuff” including apparent patterns with application to the nebular hypothesis

Patterns in Motion

All planets orbit in almost the same plane (ecliptic, AKA Zodiac)

Almost all motion is counterclockwise as seen from the north:

All planets orbit in this direction

*Almost* all planets spin in same direction

with axes more-or-less perpendicular to ecliptic

Regular moons (like our own moon) orbit in this direction, too

Planets are regularly spaced

steps increasing as we go outward

Solar Nebula Model

Planets form from disk of gas surrounding the young sun

Disk formation expected given angular momentum in collapsing cloud

Naturally explains the regular (counterclockwise) motion

Makes additional explicit predictions

Should expect planets as a regular part of the star formation process

Should see trends in composition with distance from sun

Should see “fossil” evidence of early steps of planet formation

Extra-Solar Planets

Hard to see faint planet right next to very bright star

Two indirect techniques available
(Like a binary star system but where 2nd “star” has extremely low mass)

Watch for Doppler “wobble” in position/spectrum of star

Watch for “transit” of planet which slightly dims light from star

About 100 planets discovered since 1996 See http://exoplanets.org/

Tend to be big (³Jupiter) and very close to star (easier to see)

Characteristics of “Planets”

Two types of planets

Terrestrial Planets: small, rocky material: inner solar system

Jovian Planets: large, H, He gas outer solar system

Small left-over material
provides “fossil” record of early conditions

Asteroids – mostly between orbits of Mars and Jupiter

Comets – mostly in outermost part of solar system

Meteorites – material which falls to earth

Slide 8

Evidence of Assembly Process? Craters

Craters evident on almost all small “planets”

Chapter 17: Terrestrial Planets

Earth

History, Interior, Crust, Atmosphere

The Moon

In particular origin

Mercury

Venus

Mars

Including water (and life ?)

“Comparative Planetology”

Basis for comparisons is Earth

Properties of Earth

Similarities and differences with Mars and Venus help us understand Earth better (e.g., life, greenhouse effect, etc.)

Won’t spend class time on basic properties (size, gravity, orbital period, length of day, number of moons, etc.) but you should have some relative ideas about these (see “Data Files” in text).

Timeline

Earth’s Atmosphere: Greenhouse Effect

The Moon and Mercury

No atmosphere

Cratering is evidence of final planet assembly – lots to be learned from craters

Examples of craters on the moon

Images on line at
The Lunar and Planetary Institute:
http://www.lpi.usra.edu/expmoon/lunar_missions.html

Detailed record of Apollo work at:
http://www.hq.nasa.gov/office/pao/History/alsj/frame.html

Effects of late impacts

Moon: Giant Impact Hypothesis

Explains lack of large iron core

Explains lack of “volatile” elements

Explains why moon looks a lot like earth’s mantle, minus the volatiles

Explains large angular momentum in the earth-moon system

Venus

Expect Venus to be similar to Earth?
(It isn’t!)

Venus only slightly closer to sun, so expect about same initial composition

Venus only slightly smaller than Earth, so expect about same heat flow

Venus atmosphere is dramatically different

Very thick CO₂ atmosphere

Virtually no water in atmosphere or on surface

Venus shows relatively recent volcanic activity, but no plate tectonics

Both probably related to its slightly closer position to the sun
which caused loss of its critical water

Thick atmosphere and clouds block direct view so information from:

Orbiting radar missions (Magellan in early 90’s)

Russian landers (as in previous photo)

Surface Relief of Venus from Radar

Venus does show evidence of “recent” volcanism

It does not show linear ridges, trenches, or rigid plates

In a few spots there are weak hints of this – but clearly different

Volcanoes

Sapas Mons

Lava flows from central vents

Flank eruptions

Summit caldera

Size:

250 miles diameter

1 mile high

Lava Channels

Large!

100’s of miles long

1.2 miles wide

High Venus temperatures may allow very long flows

Composition could also be different

Slide 24

Lots of Martian Science Fiction

Best, most recent and scientifically accurate is probably Kim Stanley Robinson’s series:

Red Mars, Blue Mars, Green Mars

Terraforming/colonization of Mars

Mars and the Pattern of Geologic Activity
and Atmospheric Loss

Expect intermediate geologic activity based on size

R_Mars = 0.53 R_EarthR_Moon = 0.27 R_Earth

Earth still active but lunar mare volcanism ended ~3 billion years ago

Expect intermediate atmospheric loss

Smaller size will make atmospheric escape easier

Cooler temperature (farther from sun) will make astmospheric escape harder

In some ways Mars is most “Earth-like” planet

Has polar caps

Has weather patterns

Had (in past) running water

May have had conditions necessary for development of life

Which planets can retain which gasses?

Mars atmosphere today

Pressure is only ~1% of Earth’s

Composition: 95% CO₂ 3% N₂ 2% Ar

Water:

Pressure too low for liquid water to exist

Water goes directly from solid phase to gas phase

CO₂ (dry ice) acts like this even at terrestrial atmospheric pressure

Water seen in atmosphere

Water seen in polar caps

Evidence of running water in past

Carbon dioxide (CO₂)

Gets cold enough for even this to freeze at polar caps

Unusual meteorology, as atmosphere moves from one pole to other each “year”

Mars dust storm

Sand Dunes on Mars

Spacecraft in Mars orbit

Mars Global Explorer

Mars Odyssey

Even though atmosphere is thin, high winds can create dust storms

Water ice clouds

Ancient River Channels?
(note channels older than some craters – by superposition)

Recent liquid water?
(water seeping out of underground “aquifer” ?)

Layered Deposits

Chapter 18: Worlds of the Outer Solar System

Jupiter

Condensation model

Atmospheric winds

Atmospheric chemistry

Magnetic fields

Other Jovian Planets (Saturn, Uranus, Neptune)

will only cover major differences from Jupiter

Satellites (i.e. Moons)

Jovian Planets

Ice+Rock Core H+He “Atmosphere”

Jupiter as seen by Cassini

Aurora on Jupiter

Comparison of Jovian Planets

Variation in distance presumably ultimate causes other effects

P:      Kepler’s third law

T:      Falloff mostly just result of falling solar energy

But Neptune hotter because more internal heat

M:     Clue to details of solar nebula mode

Less material in outer solar system – or perhaps less efficient capture

r:      Should drop with mass because less compression

Works for Saturn vs. Jupiter

Increase for Uranus, Neptune indicates less H, He and more heavy material

Saturn as seen by the Hubble Space Telescope

Rings are individual particles all orbiting separately

Each particle – dust to golf ball to boulder size –
is really a separate moon on its own orbit

Orbit with Keplerian velocities: high in close, slow farther out

Nearby relative velocities are low – so particles just gently bump into each other – slowly grinding themselves up

Structure in rings largely caused by gravity of moons

Comparison of Rings

All within Roche limit

Details controlled by Resonances and Shepard Satellites

Jupiter as a miniature solar system

Four large moons (Io, Europa, Ganymede, Callisto)

Regular (equatorial, circular) orbits

Pattern of changing density and composition with distance

Inner two (Io, Europa) mostly rocky, volcanic activity

Outer two (Ganymede, Callisto) more icy

Io, Europa break rules about activity

Io most volcanically active body in solar system

Europa shows new icy surface with few craters

Tidal heating explains activity

Large tides from Jupiter flex satellites

Friction from flexing heats interiors

Important for Io, Europa, some other outer solar system satellites

Possible H₂O ocean on Europa

Tidal heating may keep H₂O liquid under ice cover

Perhaps a location where life could evolve

“Europa Orbiter” Mission being planned to determine if ocean exists

Comparison of Satellites

Titan

Largest moon of Saturn

Has thick atmosphere

Pressure ~ 1 earth atmosphere

Mostly N₂, some CH₄

Gas held because of low T

UV acting on CH₄ Þ smog

Ethane produced – Lakes?

Can “see” surface only in IR

Cassini dropped a probe in early 2005.

“Code of the Lifemaker” by James P. Hogan, good sf

Ch. 19: Meteorites, Asteroids, Comets

Small bodies are not geologically active

They provide “fossil” record of early solar system

Asteroids

Mostly from region between Mars and Jupiter

Left over small debris from accretion, never assembled into a large planet

Meteorites come mostly from asteroids

Comets

“Stored” on large elliptical orbits beyond planets

Thought to be “planetesimals” from Jovian planet region, almost ejected from solar system in its early history

Meteorites provide only samples besides Apollo

With sample in hand, can perform very detailed analysis: detailed chemistry; radioisotope age; other isotope info

Asteroids

Most located between Mars and Jupiter

Largest is Ceres

1/3 diameter of moon

Most much smaller

>8,000 known

Total mass << Earth

A few make it to earth

source of the meteorites

The larger asteroids

Phobos & Deimos: Two “misplaced” asteroids?

Phobos and Diemos are small (~25 km and ~15 km diam.) moons of Mars

Look like captured asteroids rather than moons formed in place

Are “C” class – i.e. dark “Carbonaceous” type “asteroids”

Types of Meteorites

Three main kinds of meteorites

Carbonaceous chondrites: Most primitive material – dark because of C

Stones Similar to igneous rocks

Irons Metallic iron – with peculiarities

Meteors vs. Meteorites

Meteor is seen as streak in sky

Meteorite is a rock on the ground

Meteoroid is a rock in space

Meteor showers (related to comet orbits) rarely produce meteorites

Apparently most comet debris is small and doesn’t survive reentry

Meteorites can be “finds” or “falls”

For a fall – descent actually observed and sometimes orbit computed

Most have orbits with aphelion in asteroid belt

Large Meteor over the Tetons (1972)

The Leonids 2001

APOD site: Picture by Chen Huang-Ming

Meteor Showers and Comets

Meteor showers caused by large amount of small debris spread out along comet orbits

Almost none makes it to the ground – no meteorites

Occur each year as earth passes through orbit of comet

Appears to come from “radiant point” in sky

Leonids: Mid November

Comets: Hale-Bopp in April 1997

Hale-Bopp clearly shows components

Comet characteristics

Most on long elliptical orbits

Short period comets – go to outer solar system

“Jupiter family” still ~ in plane of ecliptic

“Halley family” are highly inclined to ecliptic

Longer period ones go out thousands of AU

Most of these are highly inclined to ecliptic

Become active only in inner solar system

Made of volatile ices and dust

Sun heats and vaporizes ice, releasing dust

“Dirty snowball” model

Importance of comets

Evidence of solar nebula

Source of H₂O and CO₂ for earth

Impacts continue

Impacts on Earth

Extinction of the dinosaurs

SL-9 impact on Jupiter

Pluto and Charon


	General properties of the planets
		Order, relative size, make-up (terrestrial vs. Jovian), atmosphere (including greenhouse effect)
	General properties of the interesting moons and ring systems (e.g., origin of our moon, Galilean Moons, Titan)
	Extrasolar planets (how many, how detected?)
	Comets, meteors, asteroids
		Where do they come from, what are they made of, origin of meteor showers
	Very basic stuff, most can be memorized, nothing too complex – basically what’s here in the slides


	Solar Nebula Hypothesis
		Context for Understanding Solar System
	Extrasolar Planets
		Dust Disks, Doppler Shifts, Transits and Eclipses
	Survey of the Solar System
		Terrestrial Planets
		Jovian Planets
		Other “Stuff” including apparent patterns with application to the nebular hypothesis


All planets orbit in almost the same plane (ecliptic, AKA Zodiac)
Almost all motion is counterclockwise as seen from the north:
	All planets orbit in this direction
	Almost all planets spin in same direction
		with axes more-or-less perpendicular to ecliptic
	Regular moons (like our own moon) orbit in this direction, too
Planets are regularly spaced
	steps increasing as we go outward


	Planets form from disk of gas surrounding the young sun
		Disk formation expected given angular momentum in collapsing cloud
		Naturally explains the regular (counterclockwise) motion
	Makes additional explicit predictions
		Should expect planets as a regular part of the star formation process
		Should see trends in composition with distance from sun
		Should see “fossil” evidence of early steps of planet formation


	Hard to see faint planet right next to very bright star
	Two indirect techniques available (Like a binary star system but where 2nd “star” has extremely low mass)
		Watch for Doppler “wobble” in position/spectrum of star
		Watch for “transit” of planet which slightly dims light from star









	About 100 planets discovered since 1996 See http://exoplanets.org/
	Tend to be big (³Jupiter) and very close to star (easier to see)


	Two types of planets
		Terrestrial Planets: small, rocky material: inner solar system
		Jovian Planets: large, H, He gas outer solar system

	Small left-over material provides “fossil” record of early conditions
		Asteroids – mostly between orbits of Mars and Jupiter
		Comets – mostly in outermost part of solar system
		Meteorites – material which falls to earth


	Earth
		History, Interior, Crust, Atmosphere
	The Moon
		In particular origin
	Mercury
	Venus
	Mars
		Including water (and life ?)


	Basis for comparisons is Earth
	Properties of Earth
	Similarities and differences with Mars and Venus help us understand Earth better (e.g., life, greenhouse effect, etc.)

	Won’t spend class time on basic properties (size, gravity, orbital period, length of day, number of moons, etc.) but you should have some relative ideas about these (see “Data Files” in text).


	No atmosphere

	Cratering is evidence of final planet assembly – lots to be learned from craters


	Images on line at The Lunar and Planetary Institute: http://www.lpi.usra.edu/expmoon/lunar_missions.html


	Detailed record of Apollo work at: http://www.hq.nasa.gov/office/pao/History/alsj/frame.html


	Explains lack of large iron core
	Explains lack of “volatile” elements

	Explains why moon looks a lot like earth’s mantle, minus the volatiles

	Explains large angular momentum in the earth-moon system


	Venus only slightly closer to sun, so expect about same initial composition
	Venus only slightly smaller than Earth, so expect about same heat flow

	Venus atmosphere is dramatically different
		Very thick CO₂ atmosphere
		Virtually no water in atmosphere or on surface
	Venus shows relatively recent volcanic activity, but no plate tectonics

	Both probably related to its slightly closer position to the sun which caused loss of its critical water

	Thick atmosphere and clouds block direct view so information from:
		Orbiting radar missions (Magellan in early 90’s)
		Russian landers (as in previous photo)


	Venus does show evidence of “recent” volcanism
	It does not show linear ridges, trenches, or rigid plates
		In a few spots there are weak hints of this – but clearly different


	Sapas Mons
		Lava flows from central vents
		Flank eruptions
		Summit caldera

	Size:
		250 miles diameter
		1 mile high


	Large!
		100’s of miles long
		1.2 miles wide

	High Venus temperatures may allow very long flows

	Composition could also be different


	Best, most recent and scientifically accurate is probably Kim Stanley Robinson’s series:
	Red Mars, Blue Mars, Green Mars
	Terraforming/colonization of Mars



Expect intermediate geologic activity based on size
	R_Mars = 0.53 R_EarthR_Moon = 0.27 R_Earth
	Earth still active but lunar mare volcanism ended ~3 billion years ago

Expect intermediate atmospheric loss
	Smaller size will make atmospheric escape easier
	Cooler temperature (farther from sun) will make astmospheric escape harder


In some ways Mars is most “Earth-like” planet
	Has polar caps
	Has weather patterns
	Had (in past) running water
		May have had conditions necessary for development of life


Pressure is only ~1% of Earth’s
Composition: 95% CO₂ 3% N₂ 2% Ar

Water:
	Pressure too low for liquid water to exist
		Water goes directly from solid phase to gas phase
		CO₂ (dry ice) acts like this even at terrestrial atmospheric pressure
	Water seen in atmosphere
	Water seen in polar caps
	Evidence of running water in past

Carbon dioxide (CO₂)
	Gets cold enough for even this to freeze at polar caps
	Unusual meteorology, as atmosphere moves from one pole to other each “year”


	Spacecraft in Mars orbit
		Mars Global Explorer
		Mars Odyssey

	Even though atmosphere is thin, high winds can create dust storms


Jupiter
		Condensation model
		Atmospheric winds
		Atmospheric chemistry
		Magnetic fields
	Other Jovian Planets (Saturn, Uranus, Neptune)
		will only cover major differences from Jupiter
	Satellites (i.e. Moons)


Variation in distance presumably ultimate causes other effects
	P: Kepler’s third law
	T: Falloff mostly just result of falling solar energy
		But Neptune hotter because more internal heat
	M: Clue to details of solar nebula mode
		Less material in outer solar system – or perhaps less efficient capture
	r: Should drop with mass because less compression
		Works for Saturn vs. Jupiter
		Increase for Uranus, Neptune indicates less H, He and more heavy material


	Each particle – dust to golf ball to boulder size – is really a separate moon on its own orbit
	Orbit with Keplerian velocities: high in close, slow farther out
	Nearby relative velocities are low – so particles just gently bump into each other – slowly grinding themselves up
	Structure in rings largely caused by gravity of moons


	All within Roche limit
	Details controlled by Resonances and Shepard Satellites


	Four large moons (Io, Europa, Ganymede, Callisto)
	Regular (equatorial, circular) orbits
	Pattern of changing density and composition with distance
		Inner two (Io, Europa) mostly rocky, volcanic activity
		Outer two (Ganymede, Callisto) more icy


	Io most volcanically active body in solar system
	Europa shows new icy surface with few craters


	Large tides from Jupiter flex satellites
	Friction from flexing heats interiors
	Important for Io, Europa, some other outer solar system satellites


	Tidal heating may keep H₂O liquid under ice cover

	Perhaps a location where life could evolve

	“Europa Orbiter” Mission being planned to determine if ocean exists


	Largest moon of Saturn
	Has thick atmosphere
		Pressure ~ 1 earth atmosphere
		Mostly N₂, some CH₄
		Gas held because of low T
	UV acting on CH₄ Þ smog
		Ethane produced – Lakes?
		Can “see” surface only in IR
	Cassini dropped a probe in early 2005.
	“Code of the Lifemaker” by James P. Hogan, good sf


Small bodies are not geologically active
They provide “fossil” record of early solar system
	Asteroids
		Mostly from region between Mars and Jupiter
		Left over small debris from accretion, never assembled into a large planet
		Meteorites come mostly from asteroids
	Comets
		“Stored” on large elliptical orbits beyond planets
		Thought to be “planetesimals” from Jovian planet region, almost ejected from solar system in its early history
Meteorites provide only samples besides Apollo
	With sample in hand, can perform very detailed analysis: detailed chemistry; radioisotope age; other isotope info


	Most located between Mars and Jupiter
	Largest is Ceres
		1/3 diameter of moon
		Most much smaller
	>8,000 known
	Total mass << Earth
	A few make it to earth
		source of the meteorites