Tides, Moons, Rings, and Pluto

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1 Tides, Moons, Rings, and Pluto [Oct 27, 2016] As with all course material (including homework, exams), these lecture notes are not be reproduced, redistributed, or sold in any form.

2 Ocean Tides high low

3 Ocean Tides water closer to Moon feels stronger gravitational pull. Earth Moon F = Gm 1m 2 d 2

4 Ocean Tides similarly the Earth is pulled by gravity, but less so than the ocean water closest to the Moon Moon F = Gm 1m 2 d 2

5 Ocean Tides and finally, what about the rest of the water?... Moon F = Gm 1m 2 d 2

6 Ocean Tides what would this look like from the perspective of the Earth? Moon F = Gm 1m 2 d 2

7 Ocean Tides ocean what will would be this look like from the shallower perspective of the Earth? ocean will be deeper Moon F = Gm 1m 2 d 2

8 Ocean Tides ocean will be shallower (low tide) ocean will be deeper (high tide) Earth ocean will be deeper (high tide) Moon ocean will be shallower (low tide)

9 Tides are the result of the gravitational force from the Moon and the Sun

10 Effect of the Moon on high/low tides High tide Low tide

11 Solar System more than just the planets Image not to scale solar system is much less dense than this!

12 The Galileo Mission joint US + Germany mission Launched on Oct 18, 1989 from the Space Shuttle Atlantis Goal: study Jupiter

13 The Galileo Mission Flight path included gravity assists from Venus and Earth Passed by two asteroids on its way to Jupiter Went into orbit around Jupiter in 1995; spent 8 years (35 orbits) there

14 The Galileo Mission In July, 1995, Galileo dropped this probe into Jupiter s atmosphere. After jettisoning its heat shield and deploying a parachute, it sent back ~1 hour of data before succumbing to the pressure and heat of Jupiter s atmosphere. probe is ~1.3 meters in size

15 Why name this mission after Galileo? Galileo Galilei ( )

16 Jupiter s moons 4 largest: the Galilean satellites Io, Europa, Ganymede, Callisto 67 moons now known: some are only a few km across, and are probably captured asteroids

17 Jupiter s Moons 1. Metis 2. Adrastea 3. Amalthea 4. Thebe 5. Io 6. Europa 7. Ganymede 8. Callisto 9. Themisto 10. Leda 11. Himalia 12. Lysithea 13. Elara 14. S/2000 J Iocaste 16. Praxidike 17. Harpalyke 18. Ananke 19. Isonoe 20. Erinome 21. Taygete 22. Chaldene 23. Carme 24. Pasiphae 25. S/2002 J1 26. Kalyke 27. Magaclite 28. Sinope 29. Callirrhoe 30. Euporie 31. Kale 32. Orthosie 33. Thyone 34. Euanthe 35. Hermippe 36. Pasithee 37. Eurydome 38. Aitne 39. Sponde 40. Autonoe 41. S/2003 J1 42. S/2003 J2 43. S/2003 J3 44. S/2003 J4 45. S/2003 J5 46. S/2003 J6 47. S/2003 J7 48. S/2003 J8 49. S/2003 J9 50. S/2003 J S/2003 J S/2003 J S/2003 J S/2003 J S/2003 J S/2003 J S/2003 J S/2003 J S/2003 J S/2003 J S/2003 J S/2003 J S/2003 J23

18 The Galilean Moons of Jupiter Io Europa Ganymede Callisto Semimajor axis of orbit around Jupiter: 421,000 km 671,000 km 1,070,400 km 1,882,700 km

19 Io

20 Io s volcanos Voyager Galileo Io s surface is very volcanically active- it s the youngest surface of any solar system object Numerous volcanos erupting silicate lava, with geysers erupting sulfur and sulfur dioxide Galileo orbiter found more than 100 volcanoes erupting simultaneously

21 Changes in Io s surface Voyager, 1979 Galileo, 1996

22 Interior heating in Io Jupiter 1/2 degree wobble Io Io s orbit is slightly elliptical, due to gravitational pull from Europa Tidal forces from Jupiter heat Io s interior Note- diagram not to scale! The orbital ellipticity is greatly exaggerated here. Io radiates away 100 trillion watts of power from this tidal heating

23 Europa s structure

24 Ganymede The largest moon in the solar system: radius 2634 km (larger than Mercury) Differentiated structure: iron & rocky core, mantle of ice and silicates, and crust of mostly water ice Possible liquid ocean about 200 km below the surface? Complex terrain with mountains, valleys, craters, lava flows

25 Differentiated structure of Ganymede

26 Callisto Almost as large as Mercury: radius 2403 km Very heavily cratered: one of the oldest surfaces in the Solar System possible ocean of liquid water about 100 km below the surface?

28 The Galileo Mission Mission finished in 2003, spacecraft was crashed into Jupiter s atmosphere at a speed of ~50 km/s.

29 Cassini-Huygens launched in 1997 mission: to study Saturn and its moons flyby of Earth, Venus, & Jupiter 4th probe to visit Saturn, 1st to orbit it has been orbiting since 2004 Huygens landed on Titan in 2005 mission will end in 2017

30 Saturn s Moons

32 Titan The 2nd-largest moon in the solar system, with radius 2575 km Thick, hazy atmosphere: about 1.5 times Earth s atmospheric pressure Atmosphere is primarily nitrogen, with some methane, ethane, other compounds liquid hydrocarbon lakes on the surface (methane, ethane), and liquid methane rain in the atmosphere

33 The Huygens Probe

34 Cassini images of Saturn s moons: Tethys

35 Iapetus

36 Dione

37 Rhea

38 Mimas

39 Epimetheus ra

40 Telesto

41 Hyperion

42 Enceladus

43 Recent discovery from Cassini: geysers of water ice erupting from Enceladus Probably from sub-surface pockets of liquid water

44 These plumes are most prominent at the southern pole of Enceladus.

45 Likely physical origin of plumes on Enceladus

46 Cassini in the news On Oct 28, 2015, Cassini passed by Enceladus at a distance of ~50 km (or 30 miles), which allowed it to directly study (i.e. sample) the material in the plume. One of the goals of this close flyby is to determine what molecules may be in the plume. Enceladus is particularly interesting as it may be one of the best places to search for life e.g. if it has water, energy, and complex molecules.

47 Close-up of Enceladus 1 km

52 Planetary rings

53 F = Gm 1m 2 d 2 1 r 2 log(r)

54 Planetary Rings and the Roche Limit Consider a small moon made of dust and pebbles that s held together by its own self-gravity: a rubble pile rather than a solid boulder If the moon is far away from the planet, it remains stable. Roche Limit What happens if we move the moon closer to the planet?

55 Planetary Rings and the Roche Limit As the moon gets closer to the Roche limit, it becomes distorted by the tidal pull of the planet Roche Limit

56 Planetary Rings and the Roche Limit As the moon gets closer to the Roche limit, it becomes distorted by the tidal pull of the planet Roche Limit

57 Planetary Rings and the Roche Limit At the Roche limit, the tidal forces on the moon are so strong that it begins to break up Roche Limit

58 Planetary Rings and the Roche Limit Material closer in to the planet will orbit faster than material farther out Roche Limit This makes the material gradually spread out into a ring

59 Planetary Rings and the Roche Limit Material closer in to the planet will orbit faster than material farther out Roche Limit This makes the material gradually spread out into a ring as it orbits the planet

60 Planetary Rings and the Roche Limit Eventually, we re left with a ring of small particles orbiting the planet Roche Limit

61 The Roche Limit Inside the Roche limit, material in a ring or disk can t clump together to form a single satellite, because the planet s tidal forces are too strong In this region, material ejected from impacts or collisions on moons can settle into rings orbiting the planet Rings are temporary features: over time rings will dissipate due to collisions, and particles will drift away from the rings

62 So why haven t Saturn s rings dissipated? [rings are fed by material ejected from moons e.g. plumes on Enceladus]

63 Saturn s rings Cassini s division Rings are only about 20 meters thick Composition: mostly water ice, some organic compounds and carbon Sizes from small pebbles up to large boulders

65 Saturn s rings Cassini s division is produced by the gravitational force of the moon Mimas This is due to an orbital resonance: a particle in Cassini s division would orbit twice for each one orbit of Mimas

66 Saturn s rings Huge numbers of gaps and ringlets- the rings aren t smooth! These are caused by the gravitational interaction of the ring particles with Saturn s moons and with many tiny moonlets within the ring system Some very thin rings are kept in place by shepherd satellites that prevent the ring from spreading out further

67 Shepherd moons Pandora Prometheus

68 Jupiter s ring Discovered by Voyager Ring radius is about 1.8 times Jupiter s radius Not very reflective- composted of sooty dust particles

69 Main ring is made of dust originating from moons Adrastea and Metis; gossamer rings are dust that originated from Amalthea and Thebe

70 Uranus Uranus s rings were originally discovered because they blocked the light of background stars as Uranus moved across the sky

71 Shepherd moons and Uranus s rings

72 Neptune s rings

73 Solar System more than just the planets

74 What about poor Pluto? It s very small, its moon is very large, it has a highly elliptical and inclined orbit

76 Definition of a planet Then in 2005, an object orbiting beyond Pluto but 27% more massive than Pluto was discovered: this object was named Eris So should we make Eris the tenth planet? In 2006, the International Astronomical Union convened in Prague to set the definition of a planet and settle the question A planet within the solar system is a celestial body that 1. Orbits the Sun 2. Is massive enough for its self- gravity to give it a nearly round shape 3. Has cleared the neighborhood around its orbit Objects that meet the first two criteria but not the third are dwarf planets so Pluto and Eris are both dwarf planets

77 Deciding Pluto s fate

Solar System Fact Sheet

Solar System Fact Sheet (Source: http://solarsystem.nasa.gov; http://solarviews.com) The Solar System Categories Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Rocky or Gas Rocky Rocky Rocky Rocky