Spacecraft to the Outer Solar System

Transcription

1 Spacecraft to the Outer Solar System Flybys: Pioneer 10, 11 Voyager 1, 2 Orbiters/ : Galileo, Cassini Landers (Jupiter) (Saturn) Voyager 2 is the only spacecraft to visit all four outer planets.

2 Gas Giant Planets Our goals for learning What are jovian planets like? What are the clouds like? (Jupiter as a type example) Why are there rings systems? (Saturn as a type example)

3 What are Jovian planets Like?

4 Similarities: Ring Systems All four jovian planets have ring systems, Saturn merely the most obvious. Others have smaller, darker ring particles than Saturn

5 Similarities: Interiors No solid surface. Layers under high pressure and temperatures. Strong magnetic fields => conducting materials Cores (~10 Earth masses) made of hydrogen compounds, metals & rock The layers are different for the different planets due to differences in composition and pressure.

6 Inside Jupiter (the best understood) Inside Jupiter, high pressures cause hydrogen to change phase with depth. Hydrogen acts like a metal at great depths because the hydrogen is squeezed until electrons move freely

7 Inside Jupiter Core is thought to be made of rock, with some metals, and hydrogen compounds Core is about same size as Earth but 10 times as massive

8 Subdividing the Gas Giants

9 Differences: Composition Jupiter and Saturn Mostly H and He gas Uranus and Neptune Mostly hydrogen compounds: water (H2O), methane (CH4), ammonia (NH3) Some H, He, and rock

10 Differences: Interiors Models suggest cores of jovian planets have similar composition Lower pressures inside Uranus and Neptune mean no metallic hydrogen

11 What are the Clouds Like?

12 Colors of The Gas Giants Colors are temperature controlled Decreasing temp. : increasing methane clouds methane clouds reflect blue light high thin haze Jupiter - high brown and white clouds high haze Saturn- bands deeper thicker smog haze thicker clouds. thick heavy clouds Uranus -light blue Neptune dark blue

13 Jupiter

14 Jupiter s vertical atmospheric structure Different materials form stable ice clouds at different temperatures & pressures => different clouds form at different heights

15 Jupiter convection Convection cells create a pattern of white high clouds & brown low clouds

16 Saturn

17 Uranus Early Voyager images, taken at southern summer, showed no cloud bands

18 Uranus This Hubble image shows the Uranus, system, with its ten rings and eight of its moons. In this false color image, taken in infrared light, the moving bands of cloud show up well.

19 Neptune

20 Surprising discovery or fraud? - Saturn's core is pockmarked with impact craters and dotted with volcanoes erupting basaltic lava. A. Plausible. Saturn's moons also show impact craters and volcanoes. B. Plausible. Saturn's atmosphere originated from the volatiles in impactors that were released via volcanic activity. C. Implausible. No impactors would survive the immense pressures at the depth of Saturn's core. D. Implausible. Saturn's high rotation would prevent an impactor from reaching its core Pearson Education, Inc.

21 Since there are a lot of flammable gases on Gas Giants, such as methane and propane, if you lit a match, would Jupiter burn? A. yes B. no 2014 Pearson Education, Inc.

22 What Are The Rings Like?

23 Saturn s Rings: Type Example

24 Rings made of thousands of small rings of ice particles like fluffy snowballs The B ring is sandy colored, while the outer A ring is white from ice.

25 Ring Location in Gas Giants Rings occur within 2-3 radii away (inside the Roche Limit) Region where gravity of a planet is so strong that materials can t hold together to form a moon. Planet s gravity pulls in material, moons gravities push and pull in opposite direction. Tug-o-war holds rings in place (for a while)

26 Keeping Rings in Place 1: Shepherd Moons Some rings are held in place by the gravity of tiny moons. -They are called 'Shepherd Moons' F ring has three shepherds.

27 close-up of the F ring and two shepherds. It is held between the gravity of these two moons. Prometheus (moves inside the ring) Pandora (moves outside the ring)

28 Keeping Rings in Place 2: Resonances Orbital resonance with the gravity of a larger moon can push the particles, producing a ring or a gap

29 Ring Formation in Gas Giants Rings aren t leftover from planet formation because the particles are too small to survive this long in a strong gravity field. There must be a continuous replacement of tiny particles. The most likely source is impacts with the gas giants moons.

30 Ring Formation in Gas Giants Impacts continually occur on the many small moons, chipping off fine material Fine material spreads out in orbit around the gas giant The gravity effects from the moons then hold the bits in place as rings.

31 What have we learned? What are the clouds like? The gas giant planets have different color clouds at different heights due to temperature differences They are striped because different clouds are visible due to convection plus rapid rotation causing a strong coriolis effect.

32 What have we learned? What are the rings like? The rings are tiny pieces of fluffy snow balls held in orbit 2-3 radii away from a gas giant world. They occur because gas giants have lots of moons: Impacts chip off material that becomes rings. Material is nudged into resonance orbits by the gravity of the moons, forming rings Some rings are held by the gravity of tiny shepherd moons.

33 Why don't ring particles form a moon? A. They collide too violently to accrete into a moon. B. Tidal forces from moons prevent them from accreting. C. Tidal forces from the planet prevent them from accreting. D. Their masses are too small for them to accrete Pearson Education, Inc.

34 A Wealth of Worlds: Moons of Ice and Rock Our goals for learning What kinds of moons orbit Gas Giant planets? Why are Jupiter s Galilean moons so geologically active? What is special about Titan and other major moons of the solar system?

35 What kinds of moons orbit Gas Giant planets? Small moons (< 300 km) No geological activity Medium-sized moons (300-1,500 km) Geological activity in past Large moons (> 1,500 km) Ongoing geological activity

36 Medium and Large Icy Worlds Enough self-gravity to be spherical. Metal/rock core, ice mantle and crust. Some geological activity Two main locations: Larger Icy moons orbiting gas giant planets Largest objects in Kuiper belt in the outermost solar system (Pluto, Sedna, Quoaor and others)

37 Medium & Large Moons Formed in orbit around gas giant planets. Circular orbits in same direction as planet rotation.

38 Why are Jupiter s Galilean moons so geologically active?

39 Io 12th largest world

40 Active sulfur volcanism

41 Io s Volcanic Activity Io is the most volcanically active body in the solar system, but why?

42 Tidal Heating Io is squished and stretched as it orbits Jupiter But what is causing it to stretch?

43 Every 7 days, these 3 moons line up. Orbital Resonances The tugs add up over time, making all 3 orbits elliptical, which pulls on the worlds.

44 Europa -13th largest world

45 Tidal stresses crack surface ice No surface volcanos, but millions of faults all over the surface. A few small craters are seen.

46 Europa s Ocean: Waterworld? Chaos regions: where warm ice wells up, breaks and spreads the surface.

47 Inside Europa Secondary magnetic field (requires liquid) Broken disrupted surfaces from flowing ice Surface covered in faults -some areas spread apart. Conclusion: Liquid interior layer -a global ocean

48 Europa s interior also warmed by tidal heating

49 Ganymede -8th largest world Largest moon in the solar system Surface has long fault regions, but also heavily cratered plains.

50 Ganymede Clear evidence of geological activity Tidal heating plus heat from radioactive decay? Has a magnetic Field that varies.

51 Callisto cratered iceball. No tidal heating, no orbital resonances.

52 Orbital Resonances Every 7 days, these 3 moons line up. The tugs add up over time, making all 3 orbits elliptical.

53 What have we learned? What kinds of moons orbit jovian planets? Moons of many sizes Level of geological activity depends on size Why are Jupiter s Galilean moons so geologically active? Tidal heating drives activity, leading to Io s volcanoes and ice geology on other moons

54 Saturn s Moons

55 What is special about Titan?

56 Titan s Atmosphere Titan is the only moon in the solar system to have a thick atmosphere It consists mostly of nitrogen with smog clouds that obscure the surface

57 Mosaic of Hygens Images ~5 miles high shows dark curving lines with branching tributaries (lower left). pattern is identical to desert rivers on Earth and the dry-river beds of Mars. conclude that Titan has flowing liquids eroding out channels.

58 Fish-eye Mosaic of Hygens Images mountains and a shoreline to some kind of dark-colored lake. However, at -290 F at the surface, water is frozen as hard as rock. The lake must be made of organic liquids, probably a methaneethane mix. channels mountains lake

59 Giant North Pole Lakes The biggest lake so far is 39,000 square miles, it is larger than lake Superior and about the size of the Black Sea

60 Active Methane Cycle :( There is a tiny amount of methane rainfall The lakes do not appear to grow and shrink in size There is probably not a permanent methane recycling system like Earth's water cycle

61 Saturn has 6 medium-sized moons. Mimas They are big enough to be round, but vary in their amount of geological activity. Rhea Dione Enceladus Tethys Iapetus

62 The south pole of Enceladus is covered in recent faults! This suggests some unknown, but complex, internal activity is occurring. This is a false color image taken during Cassini s approach to this moon.

63 Enceladus has live volcanic ice eruptions! The water freezes into ice particles and rises in a plume over 300 miles high. Only 3 other worlds have observed active volcanism: Earth, Io and Triton. Water eruption plume This colorized image shows the enormous extent of the faint plume.

64 Enceladus and E Ring The volcanism on Enceladus is a major source for the particles for Saturn's outer rings. Here Enceladus emits water in the middle of the E ring. E Enceladus Volcanic plume

65 Neptune s Moon Triton

66 Neptune s Moon Triton Similar to Pluto, but larger Evidence for past geological activity

67 Icy Volcanism on Triton Spouts of nitrogen geysering above the surface

68 What have we learned? What is special about Titan and other major moons of the solar system? Titan has strong active processes like Galileans Titan is the only moon with a thick atmosphere Titan is the only moon with liquid rivers and lakes. Many other major moons show signs of geological activity. 3 of gas giants have an actively volcanic moon.

69 Small Worlds Our goals for learning What are asteroids like? Why is there an asteroid belt? Where do comets come from?

70 Small Worlds are: Not round, Covered in craters, Have no atmosphere, Main surface process is mass wasting Asteroids are made of metals and rock Comets and KBOs are made of rock and volatiles

71 Asteroids

72 Asteroid Orbits Most asteroids orbit in a belt between Mars and Jupiter Trojan asteroids follow Jupiter s orbit Orbits of near-earth asteroids cross Earth s orbit

73 Origin of Asteroid Belt Rocky planetesimals between Mars and Jupiter did not accrete into a planet. Jupiter s gravity, through influence of orbital resonances, stirred up asteroid orbits and prevented their accretion into a planet.

74 Kuiper Belt Objects -Dirty snowballs

75 Two regions for small icy worlds: Kuiper belt, KBOs have orderly orbits from AU in disk of solar system Oort Cloud, worlds have random orbits out to >50,000 AU Sources for comets.

76 Growth of Tail

77 What have we learned? What are comets like? Comets are like dirty snowballs Most are far from Sun and do not have tails Tails grow when comet nears Sun and nucleus heats up Where do comets come from? Comets in plane of solar system come from Kuiper Belt Comets on random orbits come from Oort cloud