Jovian Planets Orin Harris and Greg Anderson Department of Physics & Astronomy Northeastern Illinois University Spring 2021 c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 1 / 91 Outline Overview Jovian Planets Jovian Moons Ring Systems Review c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 2 / 91 Outline Overview Orbital Periods Solar System Jovian Planets Jovian Moons Ring Systems Review Overview c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 3 / 91 Orbital Properties of Planets Name Distance (AU) Period (years) Speed (AU/yr) Mercury 0.387 0.2409 10.09 Venus 0.723 0.6152 7.384 Earth 1.0 1.0 6.283 Mars 1.524 1.881 5.09 Jupiter 5.203 11.86 2.756 Saturn 9.539 29.42 2.037 Uranus 19.19 84.01 1.435 Neptune 30.06 164.8 1.146 c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 4 / 91 M J S M J U S M J N Outline Overview Jovian Planets Jovian Planets Planetary Densities Composition Composition H & He Formation Escape Velocity Jovian Planets Formation 2 Q: Jovian Interiors Jovian Densities 02A 02 Q: Jupiter and Saturn Q: Jupiter’s composition Jovian Interiors Jovian Interiors Jupiter Jupiter Lithograph Jupiter Jupiter Jupiter from Io Interior c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 6 / 91 Jovian Planets Jupiter Saturn Uranus Neptune 3 d⊙ R⊕ M⊕ ρ (g/cm ) tilt T (K) Jupiter 5.20 AU 11.21 317.9 1.33 3.1◦ 125 Saturn 9.54 AU 9.45 95.2 0.71 26.7◦ 75 Uranus 19.19 AU 4.01 14.5 1.24 97.9◦ 60 Neptune 30.06 AU 3.88 17.1 1.67 29.◦ 60 c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 7 / 91 Planetary Densities (ρ = M/V ) 5.52 5.43 5.24 5.0 4.0 3.92 ) 3 3.0 2.0 Density (g/cm 1.0 Mercury Venus Earth Mars Saturn Uranus Neptune tNOs 0.0 Asteroids Jupiter c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 8 / 91 Composition of Jovian Planets • Hydrogen: H • Helium: He • Hydrogen Ices: Water (H2O) Ammonia (NH3) Methane (CH4) c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 9 / 91 Jovian Planet Composition • Jupiter and Saturn – mostly H and He gas – cores of hydrogen compounds, with some rock & metal • Uranus and Neptune – Mostly hydrogen compounds: water (H2O), methane (CH4) ammonia (NH3) – Some H, He, rock, metal c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 10 / 91 Jovian Planet Formation • Hydrogen compounds were more abundant in the solar nebula than rock/metal. • Beyond the frost line, planetesimals could accumulate ice. • Jovian planets grew bigger and acquired H/He atmospheres. • The Jovian cores are very similar: ≈ 10M⊕ • The biggest difference between Jovian planets is the amount of H/He gas accumulated. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 12 / 91 Escape Velocity Escape velocity: 2GM v = esc r R Thermal velocity: 3T v ∼ rms r m Loss of atmospheric component: 1 v > v rms 6 esc c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 13 / 91 Jovian Planet Formation II Why did Jupiter and Saturn capture more H and He gas? Location: Planets that form in denser parts of the nebula form their cores first. Timing: The planet that forms earliest captures the most hydrogen and helium gas. Capture ceases after the first solar wind blows the leftover gas away. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 14 / 91 Q: Jovian Interiors Why do the Jovian planet interiors differ? A) The more distant planets formed in a cooler region of the solar nebula and therefore contain a greater proportion of ices than the closer Jovian planets. B) They differ due to giant impacts at the late stages of planet formation. C) Accretion took longer further from the Sun, so the more distant planets formed their cores later and captured less gas from the solar nebula than the closer Jovian planets. D) The more distant planets had longer to form than the closer planets, since the solar nebula lasted longer at greater distances from the Sun. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 15 / 91 Q: Jovian Interiors Why do the Jovian planet interiors differ? A) The more distant planets formed in a cooler region of the solar nebula and therefore contain a greater proportion of ices than the closer Jovian planets. B) They differ due to giant impacts at the late stages of planet formation. C) Accretion took longer further from the Sun, so the more distant planets formed their cores later and captured less gas from the solar nebula than the closer Jovian planets. D) The more distant planets had longer to form than the closer planets, since the solar nebula lasted longer at greater distances from the Sun. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 15 / 91 Jovian Densities 1.5 ) Uranus and Neptune are denser 3 than Saturn because they have . 1 0 proportionately less H/He. (g/cm ρ The greater mass of Jupiter com- 0.5 presses the planet. 0 Saturn Uranus Jupiter Neptune c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 16 / 91 Q: Jupiter and Saturn Why is Saturn almost as big as Jupiter, despite its smaller mass? A) Jupiter’s greater mass compresses it more and increasing its density. B) Saturn’s rings make the planet look bigger. C) Saturn is further from the Sun, thus cooler, and therefore less compact. D) Saturn has a larger proportion of hydrogen and helium than Jupiter, and is therefore less dense. E) Jupiter’s strong magnetic field constrains its size. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 19 / 91 Q: Jupiter and Saturn Why is Saturn almost as big as Jupiter, despite its smaller mass? A) Jupiter’s greater mass compresses it more and increasing its density. B) Saturn’s rings make the planet look bigger. C) Saturn is further from the Sun, thus cooler, and therefore less compact. D) Saturn has a larger proportion of hydrogen and helium than Jupiter, and is therefore less dense. E) Jupiter’s strong magnetic field constrains its size. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 19 / 91 Q: Jupiter’s composition Overall, Jupiter’s composition is most like that of: A) Sun B) Earth C) Comets D) Asteroids c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 20 / 91 Jovian Interiors + c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 21 / 91 Jovian Interiors • No solid surface • Layers under high pressure and temperatures • Heat from sun and interiors. Jupiter, Saturn and Neptune emit more energy than they receive. Jupiter and Neptune are contracting. • All four have similar cores (∼ 10 Earth masses) made of hydrogen compounds, metals, and rock • Differences in layers that surround the core. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 22 / 91 Jupiter • Mostly H/He. No solid surface • Distance 5.20 AU • M = 318MEarth • R = 11.2REarth • ρ =1.33 g/cm3 • > 79 Moons, rings • Tcloud top = 125 K. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 23 / 91 Image Credit: NASA, ESA Magnetosphere c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 29 / 91 Saturn • Mostly H/He. No solid surface • Distance 9.54 AU • M = 95.2MEarth • R =9.4REarth • ρ =0.7 g/cm3 • > 82 Moons, rings • Tcloud top = 95 K. Animation: Saturn’s Moons c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 32 / 91 Titan Transits Saturn Moons of Saturn from Cassini, left to right: Janus, Pandora, Enceladus, Mimas, Rhea. Uranus • Hydrogen compounds, H, He • Distance 19.2 AU • M = 14.5MEarth • R =4.0REarth • ρ =1.32 g/cm3 • > 27 Moons, rings • Tcloud top = 60 K. • planet, rings, moons tipped on side c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 36 / 91 Uranus & Ariel NASA Photo: Uranus with Aurora Neptune • Hydrogen compounds, H, He • Distance 30.1 AU • M = 17.1MEarth • R =3.9REarth • ρ =1.64 g/cm3 • > 13 Moons, rings • Tcloud top = 60 K. • Triton’s retrograde orbit. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 39 / 91 Neptune Seasons (HST) c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 40 / 91 Outline Overview Jovian Planets Jovian Moons Selected Moons Moons Classified By Orbit Moons Classified By Size Jupiter and Moons Jovian Moons Jupiter’s Moons Backyard telescope pic Galilean Moons Galilean Moons Io Io Callisto Europa Tidal Heating Life on Europa? Ganymede & Callisto Saturn’s Largest Moons Saturn Moons & Rings Saturn Satellites and c 2012-2021G.Anderson.,O.Harris Ring Universe:Past,Present&Future – slide 44 / 91 Structure Moons Classified By Orbit Regular Moons: Orbits relatively close to the planet, prograde, little orbital inclination or eccentricity. Typically formed about their primary from the planetary sub-nebula. Irregular Moon: Orbits are distant, eccentric, inclined, a mixture of prograde and retrograde orbits. Irregular moons were probably captured by their parent planets. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 46 / 91 Moons Classified By Size Medium & Large Moons • Enough self-gravity to be spherical • Have substantial amounts of ice • Most formed in orbit around Jovian planets • Circular orbits in same direction as planet rotation Small Moons • Far more numerous than the medium and large moons • Not enough gravity to be spherical: potato-shaped c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 47 / 91 Jupiter’s Regular Moons 1:1 2:1 4:1 Io Europa Ganymede Callisto Moons magnified 2X Jupiter’s Moons Jupiter has at least 79 moons: 8 regular + 71 irregular.