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General Astronomy I

General Astronomy I. Saturn (& Voyagers) Chapter 23. Rotation of Jovians. Jupiter solar system's fastest slightly less than ten hours creates equatorial bulge easily seen from Earth centripetal acceleration at equator ~1.67 m/s² equatorial surface gravity ~24.79 m/s²

sebastian-sykes
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General Astronomy I

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  1. General Astronomy I Saturn (& Voyagers) Chapter 23

  2. Rotation of Jovians • Jupiter • solar system's fastest • slightly less than ten hours • creates equatorial bulge easily seen from Earth • centripetal acceleration at equator ~1.67 m/s² • equatorial surface gravity ~24.79 m/s² • net acceleration at equator ~23.12 m/s² • equatorial diameter greater than polar • equatorial diameter is 9275 km longer

  3. Rotation of Jovians • Jupiter • not solid – differential rotation in upper atmosphere • rotation of polar atmosphere ~5 minutes longer • three systems are used • System I applies from the latitudes 10° N to 10° S • 9h50m30.0s • System II elsewhere • 9h55m40.6s • System III – first defined by radio astronomers • corresponds to the rotation of magnetosphere • “official” rotation

  4. Rotation of Jovians • Saturn • System I – equatorial zone • 10 h 14 min 00 s • System II – all other latitudes • 10 h 39 min 24 s • System III – based on radio emissions • 10 h 39 min 22.4 s • very close to System II, it has largely superseded it.

  5. Rotation of Jovians • Saturn • System III – based on radio emissions from the planet • 10 h 39 min 22.4 s • very close to System II, it has largely superseded it. • While approaching Saturn in 2004, Cassini found radio rotation period had increased slightly • to ~10 h 45 m 45 s (± 36 s) • cause unknown • thought due to movement of radio source to different latitude inside Saturn (with a different rotational period)

  6. Rotation of Jovians • Saturn • March 2007, announced rotation of the radio emissions did not actually trace the rotation of planet • produced by convection of the plasma disc, independent of rotation • variance may be caused by geyser activity on Enceladus • water vapor emitted into Saturn's orbit becomes charged and “weighs down” Saturn's magnetic field • If true, no known method of determining actual rotation of core

  7. Rotation of Jovians • Saturn

  8. Rotation of Jovians • Saturn

  9. Rotation of Jovians • Saturn

  10. Rotation of Jovians • Saturn

  11. Jupiter • Missions • Pioneer 10 – Dec 1973 • Pioneer 11 – Dec 1974 • Voyager 1 – Mar 1979 • Voyager 2 – Jul 1979 • Galileo – Dec 1995* • Ulysses – Feb 1992/Feb 2004 • Cassini – Dec 2000 • New Horizons – Feb 2007

  12. Voyager • Voyager 1 • launched Sept 1977 • currently operational • longest-lasting • farthest from Earth

  13. Voyager • Voyager 1 • to be Mariner 11 • alignment of planets • Grand Tour • gas giants in 12 yrs • instead of 30 • Jupiter Jan 1979 • Saturn November 1980 • Grand Tour terminated

  14. Voyager • Voyager 1 • As of May 22, 2008 • 106.4 AU (9.90 billion miles) from Sun • more distant than any known solar-system object • light takes over 14.6 hours to reach spacecraft from Earth • Moon ~1.4 light seconds • Sun ~8.5 light minutes • Pluto averages ~5.5 light hours

  15. Voyager • Voyager 1 • as of May 2008 • 17.1 km/s relative to the sun • 3.6 AU/year • 38,400 miles per hour

  16. Voyager • Voyager 1 • most distant man-made object • most distant known Solar System object

  17. Voyager • Voyager 1 • 2003 terminate scan platform • ~2010 terminate gyro ops • >2020 power won’t operate any single instrument • RTG • Plutonium-238

  18. Voyager • Voyager 1 • estimated sufficient power for radio transmitters until at least 2025 • 48 years after launch

  19. Voyager • Web site

  20. Voyager • Voyager 2 • was to be Mariner 12 • launched Aug 1977 • most prolific probe ever • completed Grand Tour • problems • ground crews forgot to send important activation code • caused the probe to shut down its main high-gain antenna • crews established contact through low-gain antenna and activated it

  21. Voyager

  22. Voyager

  23. Jupiter – Galileo probe • Galileo • launched Oct 18 1989 • shuttle Atlantis STS-34 • arrived Dec 7, 1995 • firsts • discovered asteroid moon • orbit jupiter • launched probe into atmosphere • mission terminated Sep 14, 2005

  24. Jupiter – Galileo probe

  25. Jupiter – Galileo probe

  26. Jupiter – Galileo probe

  27. Jupiter – Galileo probe

  28. Jupiter – Galileo probe • Malfunctions • high-gain antenna • 134,000 bits/sec • low-gain 8-16 bits/sec • data compression • 160 bps • tape recorder • radiation anomalies • parachute near-failure

  29. Jupiter – Galileo probe

  30. Jupiter – Galileo probe • End of mission • cameras deactivated 17 Jan, 2002 • irrecoverable radiation damage • Io • damaged tape recorder electronics recovered • deorbited 21 Sept 2002 • 14 yrs in space/8 yrs around Jupiter • crashed into Jupiter’s atmosphere • final mission: measure Amalthea’s mass

  31. Hitchhiker’s Guide to the Jovians

  32. Hitchhiker’s Guide to the Jovians • much larger than terrestrial planets • thick atmospheres, but very inhospitable • no solid surfaces • mostly hydrogen and helium • strong atmospheric circulation (winds/storms) • cloud belt patterns • rings • multiple moons

  33. Saturn

  34. Cassini-Huygens • NASA/ESA/ASI joint mission • named for Giovanni Domenico Cassini • French-Italian • Christiaan Huygens • Dutch astronomer • launched 15 Oct 1997 • reached Saturn Orbit 1 July 2004

  35. Saturn

  36. eclipsing Sun

  37. eclipsing Sun

  38. Changing views

  39. Saturn • Named for Roman god Saturn • greek Kronos • symbol is stylized sickle • known for magnificent rings • 56 confirmed satellites

  40. Saturn – physical data • Orbit • 9.537 AU • 1.427 million km • eccentricity 0.054 • orbital inclination 2.48° • orbital period 29.45 years • period of rotation 10h47m6s • axial tilt 26.73°

  41. Saturn – physical data • Characteristics • Equatorial diameter 120,536 km • 9.449 Earths • Mass 5.685x1026 kg • 95.162 Earth • density 0.6873 g/cm3 • surface gravity 0.914 gee • mean cloudtop temperature: 93 K • albedo 0.47

  42. Saturn • comparison • ~1/3 mass of Jupiter • ~16% smaller • rotates as rapidly, but twice as oblate • no large heavy-element core • radiates ~1.8 x energy received from Sun • likely heated by liquid He droplets falling toward center

  43. Saturn • Magnetosphere • ~20 x weaker than Jupiter’s • weaker radiation belts • not inclined against rotation axis • aurorae centered around poles

  44. Saturn

  45. Saturn • Atmosphere • cloud-belt structure • not as distinct as Jupiter’s • colder: less energy to drive weather

  46. Planetary Atmospheres

  47. Saturn • Atmosphere • Three-layered cloud structure, just like on Jupiter • Fewer wind zones • much stronger winds • winds up to ~500 m/s near the equator

  48. Saturn

  49. Saturn’s colors • Cassini images • northern hemisphere is changing colors • now appears a bright blue • similar to Uranus • unobservable from Earth – rings in the way • one theory: shadows cast by rings cause yellow clouds to cool & sink, revealing deeper blue atmosphere

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