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AST 111 Lecture 20 Jovian Worlds I
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Jovian Worlds = 50 Earths
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Jovian Worlds = 1400 Earths!
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Jovian Worlds Jovian worlds are not known to have solid surfaces!* *Possibly have solid cores.
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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
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Mass vs. Size Jupiter has three times the mass of Saturn, but it is only 20% larger. Why not 3 times as large?
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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
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Adding more and more gas… Jupiter 3x more massive than Saturn, only slightly larger!
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Jovian Worlds Hydrogen, helium, and hydrogen compounds Formed beyond frost line in solar nebula So why are they so different?
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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
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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
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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
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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?
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Jovian Planet Size
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Structure of Jovian Planets Determined by: – Computer models – Lab experiments – Spacecraft Galileo spacecraft studied Jupiter – Models show some Jovian structures to be similar
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Specific Example: Jupiter Galileo dove into Jupiter’s atmosphere – Survived to 200km (0.3% Jupiter’s radius) 1.0 g / cm 3 is the density of water Pressure causes phase changes
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Structure of Jovian Planets Saturn: less gravity, H changes phase deeper Uranus and Neptune: not enough gravity to have liquid or metallic H
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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!
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Jovian Atmospheres “Atmospheres” means “cloud layer and above” – It’s what we see About 100-200 miles deep Different gases condense at different altitudes.
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Jovian Atmospheres Saturn and Jupiter have same 3-layer cloud structure Saturn: – Lower temperature – Cloud layers deeper in atmosphere – More “subdued” surface
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Jovian Atmospheres Uranus and Neptune: – COLD! – If there are NH 3, NH 4 SH and H 2 0 clouds: Buried deep within planet – Methane condenses in their upper atmospheres Slush of methane snow
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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
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Methane
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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
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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 NH 4 SH
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Why the stripes of color?
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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
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