ASTR-1010 Planetary Astronomy

1. ASTR-1010Planetary Astronomy Day - 23

2. Announcements Smartworks Chapter 9-12: Due Tuesday, Dec. 14 @1030 am Visit to the Observatory & Virtual Observations Reports due Tuesday Dec. 2. These CAN be submitted early!

3. Spring Classes Spring 2011: ASTR 1010/1011 – Planetary Astronomy ASTR 1020/1021 – Stellar Astronomy + Honors ASTR 2020 – Problems in Stellar Astronomy ASTR 3020 – Cosmology ASTR 3040 – Astrobiology

4. Statistics • Exam 1: 2: 3: • N = 53 5147 • Ave = 59.7 58.7 68.3 • Med’n = 61 56.5 68 • Mode = 51 55 68 • Stdev = 13.9 15.4 15.6 • High = 84 90.5 98 • Low = 24 26 33

5. Chapter 9Lecture Outline Worlds of Gas and Liquid – The Giant Planets

8. The Giant Planets • Jupiter and Saturn: mainly hydrogen and helium. • Uranus and Neptune: have much more water. • All these planets probably have a core of dense materials.

9. Characteristics of the Giant Planets • Called giant planets because of their mass: from 15 Earth masses (Uranus/Neptune) to 300 (Jupiter). • No solid surfaces: we just see the cloud layers in the atmospheres. • Rapid rotation. • Strong magnetic fields.

12. William Herschel discovered Uranus in 1781

13. John Adams & Urbain Le Verrier Predicted Neptune in 1846

14. Johann Galle actually discovered Neptune on September 23, 1846

16. Size Comparison of Earth, Uranus & Neptune

18. Cloud Patterns – Jupiter and Saturn Jupiter • Strong dark and light bands. • A long-lasting giant storm (Great Red Spot). • Many smaller storms. • Colors indicate complex chemistry. Saturn • Similar to Jupiter, but less pronounced.

19. Jupiter & Saturn  Jupiter: NASA/JPL/University of Arizona  Saturn: NASA and E. Karkoschka (University of Arizona)

25. Cloud Patterns – Uranus and Neptune Uranus/Neptune • Almost featureless as viewed from Earth. • More detail seen from spacecraft or infrared observations from the Hubble Space Telescope. • Weak banding. • Small, scattered bright or dark clouds. • Transient large storms (Great Dark Spot on Neptune).

26. Uranus & Neptune  Uranus  Neptune: both images NASA Jet Propulsion Laboratory (NASA-JPL)

27. Composition • Mainly light elements (hydrogen/helium). • Jupiter’s composition like that of the Sun (71% H, 27% He). • Biggest difference is the amount of massive elements. • Saturn has somewhat more than Jupiter. • Uranus/Neptune have larger fraction of massive elements.

28. Probing the Atmospheres • Density, composition, and circulation patterns vary with height. • Temperature, pressure increases downward. • Different appearance of planets from different heights of cloud layers. • Example: Clouds on Jupiter. • Ammonia (NH3) at T = 133 K. • Ammonium hydrosulfide (NH4SH) at T = 193 K. • Strong winds, storms, and jet streams.

29. Cloud Layers

31. Winds and Storms • Rapid planetary rotation results in strong Coriolis forces. This imparts a rotation to storms. • Most extreme winds are in Saturn’s atmosphere (1650 km/hr). • Alternating east/west winds make banded clouds on Jupiter. • Circulation pattern differs from planet to planet in ways not understood.

32. Wind Speeds

34. Uranus rotates on its side

35. There are a few storms in the atmosphere of Uranus

36. Neptune has a more active atmosphere than Uranus

37. Hubble Observations of Neptune

40. Internal Heat • All but Uranus have significant internal heat. • Jupiter is hotter than it would be just from sunlight. • Jupiter radiates about 65% more energy than it receives from the Sun. • Heat flows from the hot interior outward. • Heat has a big effect on the global circulation patterns.

41. The Zones and Belts are convection regions

42. Jupiter rotates faster at the equator than at the poles Polar Rotation Period 9 hr 55 min 41 sec Equatorial Rotation Period 9 hr 50 min 28 sec

43. Models of the Interior • Temperatures and pressures have been measured only in the outer layers. • Models are used to calculate interior conditions. • Giant planets have rocky cores and hot, dense interiors. • Jupiter/Saturn (gas giants) have more hydrogen and helium. • Uranus/Neptune (ice giants) have more water and ices (ammonia, methane).

44. Planetary Interiors

45. Uranus & Neptune have similar internal structures

46. Density / Compression • Density is a clue to composition. • In an uncompressed state • Hydrogen/helium (lowest density) • Water/ices • Rock • Metals (highest density) • Density can also be increased by compression from weight of upper layers. • Interiors are extremely hot and dense.

47. Origins • Jupiter / Saturn formed from accretion disk while hydrogen / helium still present. • Solar wind later blew out these gases. • Uranus / Neptune formed later, by merger of icy smaller bodies. • All four possess a rocky core. • Many details still not understood.

48. Magnetic Fields • Magnetic fields are generated by the motion of electrically charged materials. • Like having a large bar magnet in the planet. • Magnets have N and S poles. • Orientation of these at an angle to the rotation axis. • Orientations differ from planet to planet, and are not understood.

49. Magnetic Fields

50. Magnetospheres • Magnetospheres are huge (Jupiter’s 6 AU). • They interact with the solar wind. • Auroras (“Northern lights” on the Earth). • Produce strong radio waves. • Radio waves come from synchrotron emission: electrons on spiral motions in the magnetic fields.