Plan for this week

• The jovian planets• 5 major moons• Comets, asteroids, and Earth impacts

The jovian planets

The jovian planets

• All very large• All rotate very fast• All made mostly of gaseous material

Jupiter

Jupiter

The Great Red Spot

Jupiter

Saturn

Saturn

Uranus

Neptune

Neptune

Data for the jovian planets

Jovian interiors

• At the center, a dense core of rock, metal, and hydrogen compounds

• Around the core is gaseous molecules• Jupiter and Saturn

• Mostly hydrogen• Includes states of matter not found on

Earth• Uranus and Neptune

• Water, methane, hydrogen

The jovian moons

• Some of the jovian moons are far more interesting than the planets themselves

• There are more than 90 total• They come in all sizes

Small jovian moons

Medium sized jovian moons

Largejovianmoons

The jovian moons

• The largest moons in the solar system are:

1. Ganymede (Jupiter)

2. Titan (Saturn)

3. Callisto (Jupiter)

4. Io (Jupiter)

5. ‘The Moon’ (Earth)

6. Europa (Jupiter)

7. Triton (Neptune)

The Galileanmoons

The Galilean moons

• The four largest moons of Jupiter• Discovered by Galileo in the early 1600s

• Very important historically• Proved that everything does not go around the

Earth• Got Galileo in a lot of trouble!

The Galilean moons

• Io• The closest one to Jupiter• Size:

• Larger than Pluto• Smaller than Mercury

• Experiences very strong tidal forces

Tidal forces

Jupiter

(Other moons)

Io

The Galilean moons

• Io is the most geologically active place in the solar system!• Volcanoes continuously erupting• Not a single impact crater on its surface

Io

The Galilean moons

• Europa• The next moon out from Jupiter• Size:

• Larger than Pluto• Smaller than the Moon or Mercury

• Also experiences tidal forces• Surface is entirely covered with ice• May have a water ocean under the ice• A possible place for life?

Europa

Europa

The Galilean moons

• Ganymede• The largest moon in the solar system

• Larger than Pluto and Mercury!• (That’s all you need to know about it…)

Ganymede

The Galilean moons

• Callisto• The fourth one (just for completeness)

Callisto

Saturn’s moons

• Titan• Size:

• The 2nd largest moon in the solar system• Larger than both Pluto and Mercury

• The only moon in the solar system with a substantial atmosphere• Mostly nitrogen (like Earth!)• Atmospheric pressure = 1.5 x Earth’s• Wouldn’t need a space suit! (cold though…)

Titan

Pluto

• The most distant planet - if it’s a planet!• Distance: 30 - 50 AU (40 average)• Orbit = 248 years• Rotation = 6.4 Earth-days• Has one moon: Charon

• About half the size of Pluto

Pluto & Charon

Pluto & Charon

Planetary rings

• All jovian planets have ring systems• All are made of small pieces of debris• Probably unformed moons, or moons that were

broken apart by the planet’s gravity

Saturn’s rings

• Small chunks of ice (mostly)• Incredibly thin

• A single sheet of paper 3 football fields across!• Made of many ‘ringlets’

Asteroids

• Chunks of rock and metal• Mostly in the asteroid belt - but not all of ‘em!• Earth crossing asteroids

• Have orbits that bring them near Earth’s orbit

Comets

• Chunks of ice, rock, & metal (‘dirty snowballs’)• Today in two locations:

• The Kuiper belt• Beyond Neptune’s orbit• ~ 30 - 100 AU out• In the disk of the solar system

• The Oort cloud• A sphere way, way beyond Neptune• ~ 50,000 AU out

A cometnucleus

Comets

• If a comet ‘falls’ towards the Sun:• It begins to sublimate (solid --> gas)• Develops a tail• This tail always points away from the Sun

The Sun