The Outer Planets

Jovian Planet Properties

Jovian Planet Properties

• Compared to the terrestrial planets, the Jovians:• are much larger & more massive• are composed mostly of Hydrogen, Helium, &

Hydrogen compounds• have no solid surfaces• rotate more quickly• have slightly “squashed” shapes• have many moons• have ring systems

Inside the Jovian Planets• All Jovian cores appear to be similar.

• made of rock, metal, and Hydrogen compounds• 10 x the mass of Earth

• Uranus & Neptune captured less gas from the Solar nebula.• accretion of planetesimals took longer• not much time for gas capture before nebula was cleared out by Solar wind

• Only Jupiter and Saturn have high enough pressure for H & He to exist in liquid and metallic states.

Jovian Storms• We also see high pressure storms

• analogous to hurricanes, but they rotate in the opposite direction• Jupiter

• the Great Red Spot• we are not sure why it is red

• Neptune• the Great Dark Spot

The Jovian Atmospheres

• The temperature profile of each planet determines the color of its appearance.

• Cloud layers form where a particular gas condenses.

• Saturn has the same cloud layers as Jupiter.• they form deeper since Saturn is

colder overall• they are spread farther apart

since Saturn has lower gravity

• Uranus & Neptune• cold enough to form methane

clouds

Jovian Magnetospheres

• Saturn, Uranus, & Neptune have smaller & weaker magnetospheres.• fraction of electrically conducting material in interiors is smaller• Solar wind is weaker farther out, or else their magnetospheres would be even

smaller• we can not explain the magnetic field tilts of Uranus & Neptune.

Jovian Planets have Numerous Moons

• medium moons• 300 to 1,500 km in

diameter• large moons

• greater than 1,500 km in diameter

• both groups formed like planets out of the “mini-Solar nebulae” surrounding the Jovian planets

• small moons• less than 300 km across• they are not spherical• probably captured

asteroids

We can divide them into three groups:

Comparing Jovian Ring Systems

• Compared to Saturn, the other ring systems:• have fewer particles• are smaller in extent• have darker particles

• Why this is so, we are not sure.

• Other unsolved mysteries:• Uranus’ rings are eccentric

and slightly tilted from its equatorial plane.

• Neptune has partial rings.

Saturn’s spectacular rings are composed of fragments of ice and

ice-coated rock

Moons Pandora and Prometheus act as shepherd moons and keep the F ring to a band about 100km wide because of gravitational effects.

Dust spokes in Saturn’s rings

Uranus sports a hazy atmosphere with few clouds

A system of rings and satellites revolves around Uranus

Uranus’ tilt gives it very exaggerated seasons

Pluto was discovered in 1930 by Clyde Tombaugh by comparing photographs

taken a few days apart.

Pluto and its moon, Charon, are about the same

size

Origin of the Comets• The leftover icy

planetesimals are the present-day comets.

• Those which were located between the Jovian planets, if not captured, were gravitationally flung in all directions into the Oort cloud.

• Those beyond Neptune’s orbit remained in the ecliptic plane in what we call the Kuiper belt.

The nebular theory predicted the existence of the Kuiper belt 40 years before it was discovered!

The Kuiper Belt of comets spreads from

Neptune out 500 AU from the Sun

Kuiper Belt Object 1993SC - these images were taken 4.6 hours apart

Comet Kohoutek and Comet West

Comets lack tails until they enter the inner solar system

Comets often have two tails: a thin ION tail and a curving DUST tail

Anatomy of a comet

15 km long by 8 km

wideComet Halley nucleus

Comets don’t last forever

Fragmentation of Comet West shortly after passing near the Sun in 1976

(sequence of photos is from March 8 to March 24)

Dave Jewitt, Jan Fernandez, and Scott Shepard

Comet orbits are altered by

gravitational interactions with

planets

Small rocky debris peppers the solar system

• meteors• falling stars• shooting stars• bolides• fireballseach are caused by small rocks colliding with Earth’s atmosphere and heating up due to friction with the air

Shower Date of maximum intensity

Typical hourly rate

Constellation

Quadrantids January 3 40 Bootes

Lyrids April 22 15 Lyra

Eta Aquarids May4 20 Aquarius

Delta Aquarids July30 20 Aquarius

Perseids August 12 80 Perseus

Orionids October 21 20 Orion

Taurids November 4 15 Taurus

Leonids November 16 15 Leo Major

Geminids December 13 50 Gemini

Ursids December 22 15 Ursa Minor

Primary Meteor Showers

The Titius-Bode Law:

A series of numbers add 4 divide by ten measured value Planet….

0 4 0.4 0.39 Mercury

3 7 0.7 0.72 Venus

6 10 1.0 1.0 Earth

12 16 1.6 1.52 Mars

24 28 2.8

48 52 5.2 5.2 Jupiter

97 100 10.0 9.54 Saturn

192 196 19.6 19.19 Uranus

384 388 38.8 39.44 Pluto

2.8 Ceres

Neptune???

Homework #6

Use Bode’s rule to calculate how far the “eleventh” planet (lets call it planet X) should be from the Sun in our solar system.

How long is the year on planet X?