AST 111 Lecture 20 Jovian Worlds I

Jovian Worlds = 50 Earths

Jovian Worlds = 1400 Earths!

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 – hr day on Uranus and Neptune Bulges out equatorial regions Due to formation

Mass vs. Size Jupiter has three times the mass of Saturn, 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 / cm 3 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 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 NH 3, NH 4 SH and H 2 0 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 NH 4 SH

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