Astr 1050    Wed., Dec. 10, 2003

   Today: Course Evaluations

                       Chapter 18, Jovian Planets

Chapter 19, “Debris”

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)

Jupiter has multiple cloud decks as air rises in low pressure “zones”

Mostly made of H, He

Trace amounts of C, N, O, S

CH₄ present as gas

NH₃, NH₄SH, H₂O can condense in colder upper regions Þ clouds

Colors from unknown trace chemicals

Magnetic fields and trapped particles

Aurora on Jupiter

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

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

Callisto not active

Comparison of Satellites

Saturn as seen by the Hubble Space Telescope

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 will drop probe in Fall 2004

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

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

The Roche Limit
When can tides tear a moon apart?

As a planetary body get close to another object, tidal forces distort the body more and more.

Remember, Earth raises tides on the Moon
just like it raises tides on the Earth

If the distortion gets large enough, the moon will be pulled apart

Happens at “Roche Limit” when moon is
~2.44 ´ radius of planet away

At that point, tidal force pulling up on surface of moon is greater than moon’s gravity pulling down

Only matters for objects held together by gravity

Astronaut in orbit will not be pulled apart

Is held together by much stronger chemical forces

Astronaut standing on the outside of the shuttle, hoping the shuttle’s gravity would hold her there, will be pulled away from the shuttle

Comparison of Rings

All within Roche limit

Details controlled by Resonances and Shepard Satellites

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

Chapter 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

Are Asteroids Primitive?

Ida (56 km diam.) and its moon Dactyl (1.5 km diam.)

Colors have been “stretched” to show subtle differences

Imaged by Galileo on its way out to Jupiter

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”

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

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

Comet structure

Gas sublimates from nucleus

Dense coma surrounds nucleus

Ion tail is ionized gas points directly away from sun

shows emission spectrum

ions swept up in solar wind

Dust tail curves slightly outward from orbit

shows reflected sunlight

solar radiation pressure gently pushes dust out of orbit

Hale-Bopp clearly shows components

Where do comets come from?
Long period comets: The Oort Cloud

Most (original) orbits have aphelions of >1000 AU

Need ~6 trillion comets out there to produce number seen in here

Total mass of 38 M_Earth

Passing stars deflect comets in from the cloud

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

Chapter 16-19 Review

Solar Nebula

Terrestrial Planets

Properties of Earth

Greenhouse Effect (cf. Venus, Mars)

Cratering, origin of moon

Jovian Planets

Properties of Jupiter, composition, atmosphere

Moons and Rings

“Debris”

Asteroids and Comets

Chapter 16-19 Review

We’ve covered this material fast – exam will not cover subtle concepts or obscure facts. Very basic information and only the most fundamental ideas.

Things you should know include:

Order of planets in solar system, general sizes of orbits, sizes and compositions of the planets (also asteroids and comets in general, notable moons).

How these items fit into the solar nebula picture.

Chapter 16-19 Review

Example questions:

True/False:

Jupiter was probably influential in preventing the formation of a planet at the location of the asteroid belt.

The dirty snowball theory suggests that the head of a comet is composed of ices.

Jupiter radiates more heat than it absorbs from the sun.

Venus is very hot because its atmosphere is rich in CO₂.

The Greenhouse effect occurs because gases like carbon monoxide are opaque to IR radiation.

The Jovian planets have lower densities than the terrestrial planets.

Chapter 16-19 Review

Example questions:

True/False:

Meteorites appear to be composed of material similar to that found in comets.

Jupiter’s interior is mostly liquid helium.

Saturn’s rings are composed of metallic dust grains.

Flow channels on Venus suggest it was once rich in water.

The oxygen in Earth’s atmosphere was outgassed by volcanic explosions.

Mars is the third rock from the sun.

Chapter 16-19 Review

Example questions:

Multiple choice:

On a photograph of the moon, the moon measures 30 cm in diameter and a small crater measures 0.2 cm. The moon’s physical diameter is 1738 km. What is the physical diameter of the small crater?

About 1738 km

About 12 km

About 520 km

About 350 km

About 3.5 km

Chapter 16-19 Review

Example questions:

Multiple choice:

Though Titan is small, it is able to retain an atmosphere because?

It is very cold.

It is very dense.

It rotates very slowly.

It attracts gas from the solar wind.

It has a very strong magnetic field.

Exam #4

20 Multiple Choice questions, 10 true/false, 1 or 2 essay/written questions, plus 1 follow-up extra credit problem (computational and meant to be challenging).

About 1/2 of the questions covering the solar system

About 1/2 of the questions covering Chapters 12 and 13

Questions mostly cover the basics and are not intended to be subtle or tricky.

Exam #4

List of possible topics for essay questions:

Dark Matter

Cosmic Microwave Background Radiation

Extrasolar Planets

Comparative Planetology of Venus, Earth, and Mars


	Today: Course Evaluations
	Chapter 18, Jovian Planets
	Chapter 19, “Debris”


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)


	Mostly made of H, He
	Trace amounts of C, N, O, S
	CH₄ present as gas


	NH₃, NH₄SH, H₂O can condense in colder upper regions Þ clouds
	Colors from unknown trace chemicals


	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
		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 will drop probe in Fall 2004
	“Code of the Lifemaker” by James P. Hogan, good sf


	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


As a planetary body get close to another object, tidal forces distort the body more and more.
	Remember, Earth raises tides on the Moon just like it raises tides on the Earth

If the distortion gets large enough, the moon will be pulled apart
	Happens at “Roche Limit” when moon is ~2.44 ´ radius of planet away
	At that point, tidal force pulling up on surface of moon is greater than moon’s gravity pulling down

Only matters for objects held together by gravity
	Astronaut in orbit will not be pulled apart
		Is held together by much stronger chemical forces
	Astronaut standing on the outside of the shuttle, hoping the shuttle’s gravity would hold her there, will be pulled away from the shuttle


	All within Roche limit
	Details controlled by Resonances and Shepard Satellites


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


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


	Ida (56 km diam.) and its moon Dactyl (1.5 km diam.)
		Colors have been “stretched” to show subtle differences
	Imaged by Galileo on its way out to Jupiter


	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”


	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


	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


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


	Gas sublimates from nucleus
	Dense coma surrounds nucleus
	Ion tail is ionized gas points directly away from sun
		shows emission spectrum
		ions swept up in solar wind
	Dust tail curves slightly outward from orbit
		shows reflected sunlight
		solar radiation pressure gently pushes dust out of orbit


	Most (original) orbits have aphelions of >1000 AU

	Need ~6 trillion comets out there to produce number seen in here
	Total mass of 38 M_Earth

	Passing stars deflect comets in from the cloud


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


	Solar Nebula
	Terrestrial Planets
		Properties of Earth
		Greenhouse Effect (cf. Venus, Mars)
		Cratering, origin of moon
	Jovian Planets
		Properties of Jupiter, composition, atmosphere
		Moons and Rings
	“Debris”
		Asteroids and Comets


	We’ve covered this material fast – exam will not cover subtle concepts or obscure facts. Very basic information and only the most fundamental ideas.

	Things you should know include:
		Order of planets in solar system, general sizes of orbits, sizes and compositions of the planets (also asteroids and comets in general, notable moons).
		How these items fit into the solar nebula picture.


	Example questions:
	True/False:
		Jupiter was probably influential in preventing the formation of a planet at the location of the asteroid belt.
		The dirty snowball theory suggests that the head of a comet is composed of ices.
		Jupiter radiates more heat than it absorbs from the sun.
		Venus is very hot because its atmosphere is rich in CO₂.
		The Greenhouse effect occurs because gases like carbon monoxide are opaque to IR radiation.
		The Jovian planets have lower densities than the terrestrial planets.


	Example questions:
	True/False:
		Meteorites appear to be composed of material similar to that found in comets.
		Jupiter’s interior is mostly liquid helium.
		Saturn’s rings are composed of metallic dust grains.
		Flow channels on Venus suggest it was once rich in water.
		The oxygen in Earth’s atmosphere was outgassed by volcanic explosions.
		Mars is the third rock from the sun.


Example questions:
Multiple choice:
	On a photograph of the moon, the moon measures 30 cm in diameter and a small crater measures 0.2 cm. The moon’s physical diameter is 1738 km. What is the physical diameter of the small crater?
		About 1738 km
		About 12 km
		About 520 km
		About 350 km
		About 3.5 km


Example questions:
Multiple choice:
	Though Titan is small, it is able to retain an atmosphere because?
		It is very cold.
		It is very dense.
		It rotates very slowly.
		It attracts gas from the solar wind.
		It has a very strong magnetic field.


	20 Multiple Choice questions, 10 true/false, 1 or 2 essay/written questions, plus 1 follow-up extra credit problem (computational and meant to be challenging).
	About 1/2 of the questions covering the solar system
	About 1/2 of the questions covering Chapters 12 and 13
	Questions mostly cover the basics and are not intended to be subtle or tricky.


	List of possible topics for essay questions:
		Dark Matter
		Cosmic Microwave Background Radiation
		Extrasolar Planets
		Comparative Planetology of Venus, Earth, and Mars