Dr. Henry Throop / University of Colorado Astronomy 1110 June 18, 2000 Lecture 11: Jupiter & Saturn: Giants of the Solar System Announcements ------------- Exams: will be back on tuesday. HW #3: hand out Tuesday, due Thursday (not Wednesday) Tomorrow (Tuesday): meet at planetarium, Cosmic Collisions show Main Points ----------- General intro: what are the jovian planets? Larger -- gas giants Lots of moons Rings Futher apart Colder (but also giving off heat) Funny colors Magnetic fields Intro to planets ---------------- Slide show VG: mass & size, esp. relative to Earth Joop: can fit 1400 Earths inside has mass of 300 Earths (ie, much bigger than Earth, but also not as dense) Hard to think of gas as being a planet. But, we see clouds of gas all over the place! E.g., Orion Nebula, Trifid Nebula, Stars, galaxies, universe, etc. Quite true that small, km-sized cloud of dust would boil itself away. But you can think of Jupiter as being just something like the Earth (10x bigger,really) with a really, really big atmosphere. Gravity is strong enough to hold Earth's atmosphere on, and it'll do the same for Jupiter. Can't talk about surfaces, or standing on the planets. They still have layers & differentiation going on. Add more mass to Jupiter, and it actually would get smaller! Not really intuitive -- but if you add a little tiny bit more mass, gravity pulls it that much closer together. Continuum: Saturn -- Jupiter -- Br. Dw. -- Cool Star -- Hot Star Difference: More mass -> stronger force of gravity pulling it together -> dense -> hotter -> fusion? Biggest stars burn out the fastest! Jupiter is a `failed star', by factor of 80. First day -- Gl229B -- Brown Dwarf. In Jupiter, heat coming out from core, by differentiation -- _not_ by fusion. Also, Solar heat is not that important -- so far away that it gets 25x less sun per area than Earth, and neptune gets 1000x less. Light from sun ~ 1/distance^2 Demo: convection. "Hot air rises" -- since it's less dense, and gravity tugs more on the cold air than the hot stuff. Lamp at bottom heats the cold lava, makes it expand. Then it gets to top and cools off. (in joop: cools off enough to make clouds of ammonia, rain) At top, it's now cold and sinks back down. Back at bottom, warms up Cycle repeats. This is why we get rising & falling zones & belts in jupiter. Basically big lava lamp. NB: convection happens everywhere: Earth's atmosphere & core, Jupiter, Mars, Uranus, etc. Q: What's in the core of Jupiter? How do we know? A: We don't know, in sense that we've never been there, measured it. But we do know a little bit. o Know the density. From Kepler's 3rd law, which tells us mass of the planet! o No `planetquakes', no tectonics, not much else. o We do have lots of heat coming off from planet o Measure the magnetic field o Use theoretical models -- physics. Take little boxes of hydrogen, put them between diamond tips, and smash them together -- see what happens at 2 million bar (at 2Mbar, hydrogen turns into metallic liquid hydrogen) o Galileo Probe (Hot Wheels toy) o SL/9 (i.e., set off a bomb) Basically though, no surfaces, so no geology. No tectonics, no volcanism, no erosion, no impact craters! What it has is layers of atmosphere, surrounding a dense core. No seasons! Why? Rotation rates -- all pretty fast Major Processes --------------- Convection Differentiation -- thermal energy given off Chemistry in atmosphere TP's depended a lot on how far from the sun they were. But, JP's depend mostly on just how big they are. How much gravity, how much heat being given off, etc. Distance from sun is less important. Family portraits & comparisons ------------------------------ Jupiter Biggest B-field -- tilted 10 deg -- 20,000 times earth strength Biggest planet Mostly gaseous: 300 m_earth = 300 x 6e27 g Big clouds, lost of moons, small ring system Giving off lots of heat -- as much as it gets from the sun Ammonia Auroras Great red spot -- high pressure zone Four `galilean satellites' -- like a miniature little world, four planets More satellites: captured `roids Saturn Same size, but less dense, compared to Jupiter 95 m_earth Has a nice atmosphere, lots of convection -- but clouds are higher, so we can't see all the gasses in the atmo! Yellowish Billions of moons Medium-sized B-field, tilted 0 deg Mega ring system Ammonia Titan -- perhaps only place in SS besides Earth that has oceans? Uranus Tilted on its side B-field tilted 60 deg to rotation axis Thin dark rings Methane Almost totally featureless Neptune `Ring arcs' B-field tilted 46 deg to rotation axis Methane Visible white upper-atmo clouds Rings ----- Saturn's Rings Order of discovery: A, B, C, D, E, F, G Explain resonances Gravity Collision: particles can either stick, or break apart Inside `Roche zone' of planet, they're most likely to break apart (by tidal forces) Demo of rings: edge-on tilt & Early history Bi: salad dressing How did jupiter form? Two ideas: 1) like a star. Just have runaway growth: gravitational attraction 2) Make a core -- about 10x the size of Earth. Do this by just building up enough dust into boulders, asteroids, planetesimals, planets, and finally a core Then, sweep it through the nebula and it attracts all the gas around it. Runaway growth: like greenhouse: Make planet a little bit bigger It can gravitationally pull harder on gas in nebula It grows even bigger Can gravitationally pull even more etc, etc. til all the gas is gone! Collab Q's ---------- why is jupiter larger than the rocky planets Video: Auroras --------------