Upload
lindsey-cunningham
View
222
Download
0
Tags:
Embed Size (px)
Citation preview
AST 111 Lecture 20
Jovian Worlds I
Jovian Worlds
Jovian worlds are not known to have solid surfaces!*
*Possibly have solid cores.
Jovian Rotation and Shape
• They rotate rapidly– 10 hr day on Jupiter and
Saturn– 16-17 hr day on Uranus
and Neptune
• Bulges out equatorial regions
• Due to formation
Mass vs. Size
Jupiter has three times the mass ofSaturn, but it is only 20% larger.
Why not 3 times as large?
Adding more and more gas…
• Jovian worlds much like a stack of pillows
• As more gas gets added, the gas below compresses
• Keep adding gas, planet does not get larger– Gets more dense
Adding more and more gas…
Jupiter 3x more massive than Saturn, only slightly larger!
Jovian Worlds
• Hydrogen, helium, and hydrogen compounds
• Formed beyond frost line in solar nebula
• So why are they so different?
What are they made of?
• Jupiter and Saturn:– Mostly H and He– Few percent H
compounds– Little rock and metal
• Uranus and Neptune:– Less than half H and He– Primarily H compounds– Little rock and metal
Why different amounts of stuff?
• All Jovian worlds:
– Grew from ice-rich planetesimals • These were all 10x Earth’s mass
– Had enough gravity to hang onto H and He
Why different amounts of stuff?
• The “ice seeds” of the Jovian worlds:
– Packed closer together closer to the Sun
– More spread out farther from the Sun
Why different amounts of stuff?
• Icy planet seeds same mass, but:
• Farther out, took longer to form
• Had less time to acquire H and He before Sun turned on
• What does this say about Jovian planet size farther out?
Jovian Planet Size
Structure of Jovian Planets
• Determined by:– Computer models– Lab experiments– Spacecraft
• Galileo spacecraft studied Jupiter– Models show some Jovian structures to be similar
Specific Example: Jupiter
• Galileo dove into Jupiter’s atmosphere– Survived to 200km (0.3%
Jupiter’s radius)
• 1.0 g / cm3 is the density of water
• Pressure causes phase changes
Structure of Jovian Planets
• Saturn: less gravity, H changes phase deeper
• Uranus and Neptune: not enough gravity to have liquid or metallic H
Jovian Atmospheres
• On Earth, only water condenses to form clouds
• On Jovian worlds, several gases can condense to form clouds
• Hydrogen compounds responsible for colorful appearances – Ammonia: Whitish-yellow– Ammonium Hydrosulfide: Orange– Water: White– Methane: Blue, must be COLD!
Jovian Atmospheres
• “Atmospheres” means “cloud layer and above”– It’s what we see
• About 100-200 miles deep
• Different gases condense at different altitudes.
Jovian Atmospheres
• Saturn and Jupiter have same 3-layer cloud structure
• Saturn:– Lower temperature– Cloud layers deeper in
atmosphere– More “subdued” surface
Jovian Atmospheres
• Uranus and Neptune:
– COLD!
– If there are NH3, NH4SH and H20 clouds:• Buried deep within planet
– Methane condenses in their upper atmospheres• Slush of methane snow
Colors of Jovian Atmospheres
• Jupiter and Saturn
– Water and ammonia reflect white light
– Ammonium hydrosulfide reflects brown and red light
• Uranus and Neptune
– Methane gas absorbs red light
– Methane clouds reflect blue light
Methane
Wind and Storms on Jupiter
• Solar heat causes air on equator to warm, rise, move to poles– Earth has this too
• Creates “circulation cells”
• Split by Coriolis force– Stronger for faster
rotation
Why stripes of color?
• Consider the circulation cells– Rising on one edge– Falling on the other
• Rising edge brings ammonia (white) to where it can condense– Then falls as ammonia snow
• Falling edge is depleted of ammonia– We see the brownish NH4SH
Why the stripes of color?
Wind and Storms on the Others
• Bands are present on Saturn and Neptune– Slower rotation and
smaller size, fewer bands
• Also have large storms– Great Red Spot on
Jupiter– Great Dark Spot on
Neptune