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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
Large
jovian
moons
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 Galilean
moons
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
Io
(Other moons)
Jupiter
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 comet
nucleus
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