PYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 1 Announcements HW 4 due now 50% credit if handed in on Tuesday Mid-term #2 Coming up in one week Material includes everything since the last Mid-term Same format • 5-option multiple-choice questions • 1 hour – so don’t be latePYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 2 PTYS/ASTR 206 – The Golden Age of Planetary Exploration Shane Byrne – [email protected] Gas Giants: Jupiter and SaturnPYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 3 In this lecture… The frost line A two-part solar system Formation of Jupiter and Saturn Jupiter and Saturn Basics Exploration of Jupiter and Saturn Interiors of Jupiter and Saturn Metallic Hydrogen Helium rainfall Magnetic fields Atmosphere of Jupiter and Saturn Impact of comet Shoemaker-Levy 9PYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 4 We’ve been talking about the inner solar system so far Dominated by solid bodies made from rock and iron The frost line 82% M5.5% M11% M1.2% MGaspra Mathilde ErosPYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 5 The outer solar system Jupiter and beyond Gas Giants Jupiter Saturn Ice Giants Uranus Neptune Icy moons Comets Kuiper belt objects 318 MPYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 6 How did the outer solar system planets get so big? Why are all the small bodies so icy? All down to how the solar system formed. A disk dominated by hydrogen and heliumPYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 7 Temperature in the disk drops with distance from the sun At some distance water ice become stable Water is very abundant so things outside this line grow very rapidly In our solar system, this line was in the asteroid belt Inner asteroids all rock/iron Outer asteroids are icy Solid objects beyond the asteroid belt are very icy Arakawa and Kouchi, 2007PYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 8 Two basic theories on how to get started Direct collapse of part of the gas disk around the sun Instability in the disk triggers local collapse This is how stars form Accumulation of a solid rocky/icy core Core gets large - ~10 Earth Masses Starts to capture gas from the disk, gets larger etc… Formation of Jupiter and SaturnPYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 9 Once started, planets grow fast More gas captured from the disk When planets get big they grow faster by using gravitational focusing Causes oligarchic growth Big planets grow fastest Big planets gobble up all the available material Gas giants are BIG These planets need to grow fast as the disk will disappear within ~10 million years Protoplanetry disks Hubble Space TelescopePYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 10 Gas giant planets grow so large that they can clear gaps in the diskPYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 11 So what did we end up with after this… Jupiter and Saturn are mostly hydrogen and helium Rocky core (if there is one) is very small Small amounts of ammonia and water produce the nice colored clouds Jupiter Saturn Distance from Sun 5.2 AU 9.5 AU Orbital Period 12 years 29.5 years Mass (Earth-masses) 318 95 Radius (Earth-Radii) 11 9.4 Density (kg m-3) 1380 687 Rotation rate 10 hrs 10.2 hrs Magnetic field YES yes Rings yes YES Moons ~60 >> 60 Jupiter and Saturn Basics EarthPYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 12 Both planets have rings – but that’s a story for another day Jupiter Dust from asteroid collisions Saturn Chunks of ice cm to meter sizedPYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 13 Both planets have interesting Moons – but that’s another lecture (x3 !)PYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 14 Many spacecraft have visited Jupiter Jupiter commonly provides gravitational sling shots for spacecraft destined for the outer solar system Fly-bys Pioneer 10 and 11 (1973 and 1974) Voyager 1 and 2 (1979) Ulysses (1992) Cassini (2000) New Horizons (2007) Galileo orbiter and entry-probe Exploration of Jupiter and Saturn Galileo – 1995-2003 What’s wrong with this picture?PYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 15 Fewer spacecraft have visited Saturn Flybys Pioneer 11 (1979) Voyager I and II (1980 and 1981) End of Voyager I planetary encounters Voyager II went on to Uranus and Neptune Cassini orbiter Carried Huygens probe to study Titan Ongoing mission Cassini – ongoing Voyager II – 1981PYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 16 Rocky/icy core Figured out from oblate shape 2.6% of Jupiter’s mass in a core 10% of Saturn’s mass in a core Deep metallic hydrogen layer High pressure Regular hydrogen and helium near the surface Lower pressure But still like a liquid These ‘gas’ giants are more like liquid giants Interiors of Jupiter and SaturnPYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 17 Metallic Hydrogen Hydrogen is usually a gas – each atom has 1 electron orbiting 1 proton Under very high pressure electrons are not tied to a single atom Freely moving electrons make metallic hydrogen a very good conductor of electricity Like a metal! – even though it’s a liquid This pressure comes from gravity From the weight of the overlying materialPYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 18 Jupiter is still cooling off Jupiter emits 1.6 times as much energy as it absorbs from the sun This extra energy is probably left-over heat from its formation Jupiter is contracting slowly as it cools off This energy can power Jupiter’s extreme weather On Earth solar radiation powers our weather Saturn also emits more than it absorbs The source of this energy is differentPYTS/ASTR 206 – Gas Giants: Jupiter and Saturn 19 Saturn also emits more than it absorbs The source of this energy is different
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