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

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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.

Ganymede 38% Callisto 27% Europa 12% Io 23%

The four Galilean moons comprise all but .003% of the total orbiting mass.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 49 / 91

Galilean Moons

Four Galilean Moons (1610): • Io: Active volcanoes • Europa: Subsurface ocean? • Ganymede: Solar system’s largest moon • Callisto: cratered ice-ball

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 51 / 91 Galilean Moons

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 52 / 91

Io from Voyager (1979) Callisto. Europa Tidal Heating

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 57 / 91 Life on Europa?

• Surface mostly solid water ice. • Hypothesis: ocean of liquid water below the surface • Good place to look for life: liquid water + energy from tidal heat- ing.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 58 / 91 Ganymede & Callisto

Evidence for subsurface oceans on Ganymede, Callisto, but less tidal heating energy available. Did life find a way?

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 59 / 91 Saturn’s Largest Moons

Saturn has 24 regular and 58 irregular satellites. Seven of the satellites moons are medium and large moons, the largest Titan is bigger but less massive than Mercury. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 60 / 91 Saturn’s Major Rings and Moons

F

B

Tethys Mimas Rhea

Enceladus Dione

C

A

Moons magnified 10X Saturn’s Major Rings and Moons

F B Tethys Mimas Rhea

Enceladus C Dione Titan A

Moons magnified 10X Saturn’s Major Rings and Moons

Tethys Mimas Rhea Iapetus FB CA EnceladusDione Titan

Moons magnified 10X Copyright: NASA/JPL/Caltech, Illustration by David Seal Enceladus

Saturn’s Enceladus Titan Titan Titan: Liquid hydrocarbons. Titan: Liquid hydrocarbons.

Six Largest Moons of Uranus

Puck, Miranda, Ariel, Umbriel, Titania, Oberon Miranda

Uranus’s Major Moons and Rings

Ariel Miranda Umbriel Titania Oberon rings

Moons magnified 2X Neptune rings and moons

Triton

rings moons Neptune rings and moons

moonsrings Triton Neptune rings and moons

moonsrings Triton Neptune rings and moons

moonsrings Triton Outline

Overview

Jovian Planets

Jovian Moons

Ring Systems Ring Systems Roche Limit Saturn’s Rings Daphnis in Keeler Gap Ring Systems Saturn’s Rings Saturn’s Rings Jupiter Rings Uranus Rings Uranus Rings Neptune Rings Q: Saturn’s Rings Further Study

Review

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 76 / 91 Ring Systems

• All four Jovian planets have ring systems. • Proposals for creation: 1. Material from protoplanetary disk inside the Roche limit. 2. Debris from moon(s) disrupted by impacts. 3. Debris from moons(s) disrupted by tidal stresses when they passed inside the Roche limit. 4. Ejecta from volcanoes on moons.

• Shepherd moons & orbital resonances Shepherd moon: a moon orbiting near the edge of a planetary ring.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 77 / 91 Image Credit: astronoo.com Saturn’s Rings & Eclipsed Sun from Cassini spacecraft Daphnis in Keeler Gap Saturn’s Rings

• Most extensive ring system in Solar System

• 99.9% H20 ice • Main rings thickness: 10m . thickness . 1km • Main rings 1cm . particle size . 10m • “Gaps” regions of low density produced by i) moons or obital resonances. • Origin: old? young? no concensus.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 81 / 91

Jupiter Rings

Rings of Jupiter, Keck telescope IR image. Jupiter’s rings are faint

c 2012-2021G.Anderson.,O.Harrisand are mostly made of dust. Universe:Past,Present&Future – slide 83 / 91 Rings of Uranus

Composite Image: Rings of Neptune Q: Saturn’s Rings

How thick are Saturn’s rings from top to bottom? A) a few million kilometers B) a few tens of thousands of kilometers C) a few hundred kilometers D) a few kilometers E) a few tens of meters to a kilometer

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 87 / 91 Further Study

• Ganymede Global Map (YouTube) • Jupiters Red Spot Jupiter Red Spot (Video • Jupiter Video

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 88 / 91 Outline

Overview

Jovian Planets

Jovian Moons

Ring Systems

Review Review Review II Review

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 89 / 91 Review

• How do the density, mass and composition of Jovian planets compare to terrestrial planets? • Describe how and why the composition of Jovian planets differ. • What objects in the solar system are mostly made of hydrogen and helium? • How does the magnetic field of Jupiter compare to Earth? • What makes Jupiter denser than Saturn? • What gives Neptune and Uranus a blue color?

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 90 / 91 Review II

• What are the names of the four Galilean moons of Jupiter? • Why are icy moons more likely to be geologically active than rocky moons? • What mechanism is responsible for most of the internal heat on Io? • Which Jovian planets have rings? • How thick are Saturn’s rings? What are they made of? • What are the differences between regular and irregular moons?

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