Chapter 22-Jupiter and Saturn PDF

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Prof. Vera Gluscevic...

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Chapter 22: Jupiter and Saturn !

- have atmosphere but no solid ground & spins quickly => oblate than Earth! - Interior: mostly helium&hydrogen (J&S), ice (U&N) => lower density! - Why the difference: the Frost Line (hydrogen compounds beyond the fros line)! - Increasing mass doesn’t necessarily mean an increase in radius = adding a mass would rather increase its density bc gas is “compressible” => size of Jupiter and Saturn is similar despite the large difference in mass

- All four gas/ice giants have rings! • The particles in the rings have to be continually replenished (by small disruptive impacts)! • Formation: when small moons stray too close to the planet, inside “The Roche limit”—the distance at which the tidal forces the planet exerts on the moon exceed the gravitational forces holding the moon together.! • All four giant planets have moons within the Roche limit that continually supply ring material. ! + Why don’t terrestrial planets have rings? • The Roche limit for Earth is between 9000-18000km from its center (Moon is at 384,000 km)! • Phobos and Deimos are well outside Mars’ Roche limit too! • Terrestrial planets have few or no moons, and would not be able to continually replenish rings!

! 1. Characteristics!

- Largest planet in the solar system: x1400 of Earth! - Mass 318x Earth’s mass! 1

- Outer layer is not sold & spins so rapidly that it’s oblate (squashed on the pole and bulges around the equator)!

- Has 79 satellites (moons)! - Has one ring which is not visible from Earth! - Gives off 1.7 times the energy (infrared light) it receives from the Sun. (Jupiter’s heat > Sun’s heat)!

2. Interior!

- no solid surface! - Density 1.33 g/cm^3 (much lower compare to Earth’s 5.51 g/cm^3)! - Bizarre and unusual liquid and metallic phases of hydrogen and helium! - Cloud tops -> gaseous hydrogen -> liquid hydrogen -> metallic hydrogen -> core of rock/metals/hydrogen compounds (pressures and temperatures getting insanely high)!

3. Rotation and Storms!

- Rotates in 10 hours (a day is 10 hours)! - Fast rotation stretches storms into colorful bands surrounding the entire planet! - Winds as high as 250 mph in the outer layers, because of rotation.! - Swirling storm—Coriolis force causes deflection of winds! - The Great Red Spot! • Anticyclone (high pressure) larger than the whole planet Earth.! • Persisted 180-345 years (lasts for centuries), but is shrinking now.!

4. Layers of clouds!

- Different volatiles condense at different temperatures, forming colorful layers of clouds at different depths of Jupiter’s atmosphere:!

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• high: frozen ammonia crystals, white/yellow! • Middle: ammonium hydrosulfide, ~50km below, red/brown! • Low: water clouds, ~100 km below.!

5. Jupiter’s Magnetosphere!

- Jupiter’s Aurora—lots of electrical currents and particles raining down on Jupiter’s atmosphere (composite image is visible +UV)! • “footpoints” of Galilean moons can also be seen. What would cause an electrical connection between a moon and its planet?!

- Particles supplied by volcanic eruptions on Io (very active)! • The Io flux tube is an electric circuit connecting Io to Jupiter.!

6. Jupiter Near-Polar Orbiter (JUNO) Mission!

- Arrived at Jupiter July 4, 2016. ! - In polar orbit around Jupiter, doing one 2-hour pass every 53 days.! - Scientific goals:! a. Composition! b. Magnetosphere! c. Rocky core?! d. Amount of water present!

- Findings! a. Southern pole covered with cyclones (are these transient?)! b. Poles show lightnings.!

7. Jupiter’s “mini solar system” = Moons

- Jupiter has 79 moons, and also has gravitational control over thousands of smaller bodies (asteroids, etc.)! 3

- Only 8 moons in “regular” orbits: formed along with Jupiter in solar nebula! - Remainder are in irregular, eccentric, and inclined orbits: captured.! - Four largest moons: Io, Ganymede, and Callisto were discovered by Galileo in 1609/1610!

- Composition! • Jovian moons formed in the outer solar system where rocky and icy planetesimals formed.! • Made of rocks & ice with an iron core (largest only)! • Io is rocky, but Europa and Ganymede have an icy crust with ice or oceans underneath.! - Synchronous Rotation! • Earth’s moon and nearly all jovian moons share this trait.! • Tidal friction slows down the planet’s rotation and causes the moon to move farther out. ! • Similarly, planet’s gravity slows down the moon’s rotation till the same face of the moon is always facing the planet.!

- Orbital Resonance! • Tidal heating at Io: proximity to Jupiter and elliptical orbit push and pull on Io, generating internal friction.! • Mercury, Earth’s Moon and Mars have all lost their internal heat during the last several billion years.! • Io exhibits volcanism on a “global” scale: this is caused by tidal heating! • Temperatures in Io volcanoes can exceed 3,500 degrees F! • Ganymede completes one orbit for each 2 Europa orbits and 4 Io orbits: all three satellites line up once every 7 days, tugging on one-another => Europa and Ganymede participate in orbital resonance with Io! • Tug distorts Io’s and Europa’s orbits into ellipses, amplifying tidal heating from Jupiter.! a. Io! 4

• 400 active volcanoes: the most geologically active object in the solar system.! • 3600 km in diameter (slightly larger than Earth’s moon)! • Highest density! b. Europa

- very few impact craters on Europa (those that remain are already overlaid by new fractures)!

- Surface also shows regions that have “rafted” across! - Interior of Europa most likely looks like: ice covering + liquid ocean under ice (global ocean)!

- Hubble Space Telescope has detected plumes of water shooting off the surface of Europa! c. Ganymede!

- Largest moon in the solar system: 5,268 km diameter (larger than Mercury) - Composed of equal parts of water ice and rock! - Surface shows varying bombardment activity, and boundaries between new and old surfaces.!

- Ganymede’s magnetic field has two components: one is its own, and the other caused by Jupiter’s rotation. (=> fluid interior)

- Taken together, these could mean at least partial coverage by an interior ocean of liquid water.!

1. Characteristics!

- Second largest planet in solar system! - Has at least 82 moons*! - Perihelion and aphelion: 9.025 AU - 10.086 AU! - Orbital period: 29.46 years! 5

- Radius 54,000 - 60,000 km! - 95x more massive than Earth!

2) Cassini-Huygens!

- Cassini spacecraft reached Saturn and entered orbit on July 1, 2004. Mission ended September 15, 2017.!

- Huygens probe parachuted into Titan on January 14, 2005. Descent took 2.5 hours.! • Surface lakes and rivers of hydrocarbons and methane.! • Hundreds of times more liquid hydrocarbons than all the known oil and natural gas reserves on Earth!

3) Saturn’s Titan (moon)!

- Larger than Mercury, Titan was discovered by Christian Huygens is 1656.! - Has atmosphere !!! (composition similar to Earth’s) — 98.6% nitrogen, remainder is methane and hydrocarbons! • Ammonia was broken down by solar radiation to give nitrogen! • Breakdown of methane gives hydrocarbons! • Clouds of ethane can form, and a methane cycle seems to exist on the moon! • Why? It’s much colder at Titan, so gases don’t move as fast.!

- Possibly has oceans and volcanoes! - Tholins: Dunes of “tholins” cover vast areas of Titan’s surface and give reddish color to various features on the outer Solar System objects.!

- What’s missing for life?! • Surface temperature is -290 degrees F! • Metabolism and chemical reactions would be extremely slow at these temperatures! • Enduring source of heat is missing, except possibly the oxidization of acetylene.! 4) Enceladus!

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- September 15, 2015 NASA News Release: Enceladus has “global ocean”! - Global ocean is in contact with rocky mantle below, allowing for exchange of minerals and organics!

- Is geologically active: Cassini has detected geysers (or cryovolcanoes) of liquid water and ice in the southern hemisphere.!

- In 2015, Cassini flew through water plumes on Enceladus.! +Mimas looks like the Death Star from Star Wars!

5) The Rings of Saturn

- Large rings made up of rock and ice chunks (A~F ring) and very thin (tens of meters)! - Galileo on Saturn: “the planet Saturn is not alone, but is composed of three, which almost touch one another and never move nor change with respect to one another.”!

- Christian Huygens suggests in 1655 that Saturn has rings. ! - Giovanni Cassini (1675) noted several rings with gaps in between, most notably Cassini Division.!

- E ring discovered in 1967, originated from Enceladus.

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