The Jovian Planets and Their Moons

Transcription

1 The Jovian Planets and Their Moons Jupiter 1

2 Physical Properties of Earth and Jupiter Jupiter Earth Equatorial lradius 11.2 R Earth 6378 km Mass 318 M Earth kg Average Density 1.34 g/cm g/cm 3 Surface Gravity 2.54 Earth gravities 9.8 m/s 2 (at the base of the clouds) Escape Velocity 61 km/s 11.2 km/s Surface Temperature -120 o C at the cloud tops -50 o C to 50 o C Average Albedo (mostly from clouds) The length of a Jovian day is about 10 hours. Falling Rising Belts sinking, low pressure regions. Zones rising, high pressure regions. Why are belts dark and zones white? 2

3 Jupiter s Atmosphere 200 Clear hydrogen -100 K Thickness of atmosphere is about 1000 km. Altitude (km) Ammonia 150 Ammonia K Ammonia Hydrosulfide 200 K Water 270 K No sharp boundary between gaseous atmosphere and liquid interior. Atmosphere gradually thickens and becomes liquid with transformation complete at a depth of about 1000 km. Cloud colors due to ammonia hydrosulfide and photochemical reactions involving sulfur and phosphorus K Wind speeds ~ hundreds of km per hour. Motion of Zones and Belts Why such high wind speeds? Why is the circulation in parallel bands? Why does Jupiter emit 3

4 Jupiter s Great Red Spot a cyclonic storm that has continued for more than 300 years. Jovian Thunderstorms Lightning flashes are as much as a thousand times as powerful as those on Earth. What causes thunderstorms? 4

5 Jupiter s Aurora Oval What causes aurorae? Jupiter s Magnetic Field Jovian magnetic field is more than 10 times stronger than Earth s magnetic field. Why? 5

6 Internal Structure of Jupiter Molecular Hydrogen Liquid Metallic Hydrogen Rocky Core Jupiter s Ring System Jupiter s rings are made of dark dust with a rocky composition. How do we know this? Rings are not permanent but Rings are not permanent but are replenished by dust knocked off satellites by micrometeorite impacts. 6

7 Galilean Satellite Interior Models r = 1820 km ρ = 3.55 g/cm 3 Io Europa r = 1565 km ρ = 3 g/cm 3 Ganymede Callisto r = 2640 km ρ = 1.9 g/cm 3 r = 2420 km ρ = 1.79 g/cm 3 Mercury: r = 2439 km Moon: r = 1738 km Jupiter has more than 60 moons. Io in Jupiter s Shadow Hottest terrestrial volcanoes have maximum temperatures of about 2240 o F. Pillan Patera Temperature between 2600 and 3140 o F. 7

8 Pele, Pillan Patera, and a New Volcano Io is the geologically most active object in the solar system. Pilan Patera A new eruption Pele Eruptions powered by sulfur dioxide. Volcanic Plumes as high as 500 km. Source of Io s Heat Heat of Formation? No. Because of its small size, it cooled rapidly after it formed. Radioactive Decay? No. A small object would have very little naturally radioactive material. The small amount of heat generated would be quickly lost. Tidal Heating. Yes. The continual flexing of a moon s crust due to tidal interactions with the planet and/or other moons would effectively heat the moon, especially if its orbit is elliptical. P Ganymed e = 2 P Europa = 4 P Io. Tides on Io as high as 100 m.` 8

9 Io Flux Tube Base of Io Flux Tube Europa s Surface What does the smoothness of Europa s crust tell us about its interior? 9

10 Model of Europa s Interior Relatively clean, icy crust Metallic Core Rock Liquid Water The Galileo probe measurements of the magnetic field induced in Europa by Jupiter s rapidly rotating magnetic field demonstrate that under a brittle crust, there is a shell of salty water. Ganymede 10

11 Model of Ganymede s Interior Icy Mantle Metallic Core Icy Crust Callisto 11

12 Model of Callisto s Interior Crust a mixture of ice and rock Thin shell of liquid water Mixture of ice and rock Saturn and its Moons 12

13 Physical Properties of Jupiter and Saturn Saturn Jupiter Equatorial lradius 10.2 R Earth 11.2 R Earth Mass 95.2 M Earth 318 M Earth Average Density 0.69 g/cm g/cm 3 Gravity at the base of 1.16 Earth gravities 2.54 Earth gravities clouds Escape Velocity 35.6 km/s 61 km/s Surface Temperature -180 o C at the cloud tops -120 o C at the cloud tops Average Albedo Cassini Division Saturn Compared with Jupiter 13

14 Comparison of the Atmospheres of Jupiter and Saturn Jupiter Saturn K K Clear hydrogen Clear Hydrogen Altitude (km) Ammonia 150 Ammonia K Ammonia Hydrosulfide 200 K Water 270 K Altitude (km) Methane Haze Ammonia 150 K Ammonia Hydrosulfide 200 K K -300 Water 270 K Oblateness Rotation Axis a b ε= a b a Planet Oblateness Mercury 0 Venus 0 Earth Mars Jupiter Saturn Note: In order for an object to move in a circle, it must experience a force toward the center of the circle. This force is called the centripetal force. 14

15 What determines the internal temperature of a planet? Primordial Internal Heat or Heat from Radioactive Decay Sunlight The planet s albedo. For Saturn, helium rain also heats up the interior. As the liquid helium droplets fall through the less dense liquid hydrogen, gravitational potential energy is converted into thermal energy. Comparison of Internal Structures of Saturn and Jupiter 15

16 Saturn and its Moons Satellite Distance from Saturn (km) Radius (km) Mass (kg) Mimas 186, Enceladus 238, Tethys 295, Dione 377, Titan 1,220, Iapetus 3,560, Titan s Atmosphere 95% Nitrogen + CH 4 + C 2 H

17 Artist s View of Huygens Descent to Titan s Surface Chunks of Ice on Titan s Surface 17

18 River Channels on Titan Tethys 3 km deep crack R = 1060km 18

19 Mimas R = 196 km Enceladus Albedo = 0.9 R = 250 km 19

20 Iapetus R = 720 km Dione R = 560 km 20

21 Problem 1: Calculate the period of revolution of Mimas around Saturn GMP = 4π a 2 3 4π a P = M = kg a = 186,000 km GM G = Nm 2 /kg ( 4π )( m) P = Nm kg ( ) P = s = 0.95day Problem 2: Calculate Mimas average density. M density = M = kg R = 398 km V R V = π = π ( m) 3 V = m kg density = m 3 = 1100kg / m False Color Image of Saturn s Rings C Cassini Division B A The radius of the inner edge of the Cassini division is 117,500 km. Particles at this distance have an orbital period of day. How does this account for the existence of the Cassini division? What is the orbital period of Mimas? 21

22 Shepherding Satellites Saturn s F ring Shepherding Satellites Coorbital Satellites (Janus and Epimetheus) Dimensions of Janus: 110 km 80 km 100 km Dimensions of Epimetheus: 110 km 80 km 100 km Radius of Janus Orbit : 151,470 km Radius of Epimetheus Orbit: 151,420 km B F F A on B A A F B on A B A takes energy from B, and B gives energy to A. B will eventually catch up to A, and the two moons will again exchange orbits. 22

23 Uranus and Neptune Physical Properties of Uranus and Neptune Uranus Neptune Equatorial lradius 398R 3.98 Earth 381R 3.81 Earth Mass 14.5 M Earth 17.1 M Earth Average Density 1.29 g/cm g/cm 3 Gravity at the base of Earth gravities 1.19 Earth gravities clouds Escape Velocity 22 km/s 25 km/s Surface Temperature -220 o C -216 o C at the cloud tops Average Albedo

24 Why is it blue? Visual Image of Uranus Visual Image of Uranus Enhanced to Show Bands Internal Structure hydrogen + helium rocky slush heavy elements Diamonds in core? Source of excess thermal energy? 24

25 Oberon R = 775 km Large fault Flooded crater floors 25

26 Titania No large craters R = 805 km Umbriel R = 585 km Dark (albedo = 0.16) Heavily craterd Absence of faults 26

27 Ariel R = 580 km Lots of faults Brightest surface Smoothed by flooding Orbital resonance with Miranda and Umbriel Miranda Faults, ice-lava flows Rotated blocks of ice R = 242 km 27

28 Uranus Rings Thin layer of dark boulders. Neptune 28

29 Triton Nitrogen frost. Geysers and dark smudges. Radius = 1360 km Nearly circular orbit, but retrograde. Almost no craters. Icy greenhouse effect. Tidal forces when captured (?) by Neptune? Neptune s Rings 29

30 Nereid Large, elongated orbit. Radius = 170 km Twisted Ring in the Neptune Ring System 30