Giant Planets

1. Giant Planets Jupiter, Saturn, Uranus, Neptune

2. Size Comparison Jupiter: 318 Earth-masses, Saturn: 95, Uranus: 14.5, Neptune: 17.2 Two subclasses: Jupiter-Saturn and Uranus-Neptune

3. Terrestrial planets • low mass • high density • slow rotators ( 24 hours) • few satellites • close to Sun ( 1.6 AU) • Thin atmospheres • Weak or no magnetic field • Giant planets • high mass • low density • rapid rotators (18 hours) • many satellites • far from Sun ( 5 AU) • Thick atmospheres • Strong magnetic field

4. Jupiter, Saturn, Uranus, and Neptune have all been visited by the Voyager space probes. • Galileo is now studying Jupiter • Cassini is on its way to Saturn • Jupiter, Saturn, Uranus, and Neptune are all massive bodies • formed in outer part of pre-solar nebula where ices condense • growth by accretion and coalescence • Giant planets are gaseous/fluid bodies • supported by balance between pressure and gravity: Hydrostatic equilibrium

5. Solar Nebula Composition 98% of the nebula was in the form of gaseous H2 and He. 2% consisted of H2O, CH4, and NH3, (ices), and even smaller amounts of rocks and metals (olivines, pyroxenes, iron, nickel, etc.). Jupiter is closest to “solar” composition Saturn less H2 and He Uranus and Neptune mostly ices

6. Mass-Size-Composition The physical size of a planet depends on both its mass and its chemical composition.

8. Cross-sections

9. Chemistry of a Giant Planet

10. Atmospheres of Jovian Planets • Jupiter and Saturn • For both planets, methane and frozen ammonia (NH3) crystals are common. • For Saturn, the NH3 extends over a greater depth and is harder to see through, giving the planet a uniformly hazy appearance • Uranus and Neptune • For both planets only methane (CH4) in  atmospheres; NH3 completely frozen out. • Uranus and Neptune have a greenish-blue appearance because methane absorbs red light. • Rapid differential rotation of giant planets stretches clouds into bands. • The different colored bands in Jupiter’s atmosphere show convective motion. • Zones: Higher, cooler, lighter colors • Belts: Lower, warmer, darker colors

11. Colors • Jupiter -- reds and browns (ammonia, sulfur compounds, methane) • Saturn -- reds and yellows (ammonia, sulfur compounds, methane) • Uranus -- blues and greens (mostly from methane gas) • Neptune -- blue (from methane gas)

12. Giant Planet Atmospheres Voyager radio and infrared measurements. Temperatures are lower farther from Sun except for Neptune. Jupiter’s clouds are narrower because of strong gravity.

13. Rotation and Magnetic Axes

14. Giant Planet Magnetic Fields • At very high pressures inside Jupiter and Saturn hydrogen begins to act like a liquid metal This provides an electrically conducting fluid in which a magnetic field is generated. • In Uranus and Neptune the magnetic fields are generated by convection of water, ammonia and methane. • Jupiter and Saturn have very strong magnetic fields which are closely aligned with the planet's spin axis • The magnetic fields of Uranus and Neptune are weaker, irregular and highly tilted with respect to the planet's rotation axis.

15. Magnetospheres of Giant Planets

18. Cloud Bands on Jupiter and Saturn

19. Jupiter Atmosphere: Zonal Flow • This color "movie" depicts changes in some of the bands in Jupiter's atmosphere -- a complete circumference from 60° north to 60° south -- over 24 rotations between October 31 and November 9, 2000. The Great Red Spot is visible at lower left of center.

21. Jupiter’s Great Red Spot The Great Red Spot is a huge storm measuring 12,000 by 25,000 km (7,500 by 15,500 miles), which is big enough to hold two Earths side by side. While Jupiter's cloud patterns can change within hours or days like on Earth, the Spot has lasted for over 300 years.

22. Modern infrared observations and the counter-clockwise direction of its rotation suggest that the Spot is a high-pressure region whose cloud tops are significantly higher and colder than surrounding regions. There are other, if smaller, storm spots on Jupiter, and similar storms have been seen on Saturn and Nepture. Jupiter’s Great Red Spot

23. Jupiter Atmosphere: Heat and Depth Variation The image on the left was taken in IR light, while the image on the right is in visible light. There is a slight mismatch in the rotation, but you can see that the Great Red Spot (GRS) just below center in the right-hand image is cold and formed high in the atmosphere. The white clouds are also high and cold, the brownish clouds deeper and warmer, and the blue clouds the deepest and warmest. The deeper, hotter parts of the atmosphere glow more brightly in the IR, and by correlating the IR "hot spots" with the clouds, depth is determined.

24. Jupiter’s Interior

25. Jupiter’s Internal Sources of Energy Jupiter radiates 1.6 times a much energy as falls on it from the Sun. Thus, Jupiter has an internal heat source. It is thought that much of this heat is residual heat left over from the original collapse of the primordial nebula to form the Solar System, but some may come from slow contraction. This internal heat source is presumably responsible for driving the complex weather pattern in its atmosphere, unlike the Earth where the primary heat source driving the weather is the Sun.

26. Discoverer: Unknown Spacecraft Encounters: Pioneer 11 (1979); Voyager 1 & 2 (1980, 1981)Cassini - Huygens (2004) Mean Distance from the Sun: 9.539 AU Length of Year: 29.46 Earth years Rotation Period: 10.66 hours Mean Orbital Velocity: 9.64 km/s (6 mi/s) Inclination of Axis: 26.73 degrees Diameter: 120,536 km (74,901 mi) Number of Observed Satellites: >25 Comparisons With Earth: Diameter: 9.4 X Earth's Average Distance from the Sun: 9.5 X Earth's Mass: 95 X Earth's Density: 0.13 X Earth's Saturn Facts

27. Saturn’s High-Velocity Winds There are extremely high velocity winds in the atmosphere of Saturn. Unlike the case for Jupiter, the variations in wind speeds are not strongly correlated with the positions of the belts and bands. The wind speeds in the atmosphere of Saturn have been measured to be as high as 1800 km/hr, which is about 4 times the highest speeds in the atmosphere of Jupiter. Saturn’s Surface The surface of Saturn bears many similarities with the surface of Jupiter, but the color contrast is generally less. This is thought to be due to Saturn being colder than Jupiter (further from the Sun, but also smaller with less internal heat), so it has different chemical reactions in its atmosphere, leading to different coloration. There are large anticyclonic cells on the surface, apparently driven by the planet's internal heat source, but none are as large as the Great Red Spot on Jupiter, and they are not as abundant as on Jupiter.

30. Cassini-Huygens 1997 launch – 2004 Saturn arrival The Cassini Orbiter's mission consists of delivering a probe (called Huygens, provided by ESA) to Titan, and then remaining in orbit around Saturn for detailed studies of the planet and its rings and satellites.

31. Cassini-Huygens at Saturn The international Cassini-Huygens mission successfully entered orbit around Saturn at 9:12 p.m. PDT on June 30, 2004. This begins a four-year study of the giant planet, its majestic rings and 31 known moons.

32. Saturn’s Rings The best view of Saturn's rings in the ultraviolet indicates there is more ice toward the outer part of the rings, than in the inner part, hinting at the origins of the rings and their evolution.

33. Saturn’s Rings Nine days before it entered orbit, Cassini spacecraft captured this exquisite natural color view of Saturn's rings. The brightest part of the rings, curving from the upper right to the lower left in the image, is the B ring. Saturn's rings are made primarily of water ice. Since pure water ice is white, it is believed that different colors in the rings reflect different amounts of contamination by other materials such as rock or carbon compounds.

34. Saturn’s Rings The varying temperatures of Saturn's rings are depicted here in this false-color image from the Cassini spacecraft. The data show that the opaque region of the rings, like the outer A ring (on the far right) and the middle B ring, are cooler, while more transparent sections, like the Cassini Division (in red just inside the A ring) or the inner C ring (shown in yellow and red), are relatively warmer.

35. Uranus Uranus is the 3rd of the Gas Giant planets, and the first planet discovered in "modern" times (1781). It is barely visible from the Earth without a telescope, which explains why it was not known as a planet to the ancients, and why it had been observed various times after the telescope had been invented without the observers realizing that it was a planet and not a star. Documented sightings go back to at least 1690 when Flamsteed catalogued it as a star.

36. Discoverer: Sir William Hershel (1781) Uranus Facts Spacecraft Encounter(s): Voyager 2 (1986) Mean distance from Sun: 19.19 AU (2.871 billion km/1.784 billion mi) Length of year: 84.01 Earth years Rotation period: 17.24 hours Mean orbital velocity: 6.81 km/s (4.2 m/s) Inclination of axis: 97.92° Diameter: 51,118 km Number of Observed Satellites: >20 Diameter: 4.0 x Earth's Mean Distance from Sun: 19.2 x Earth's Mass: 14.5 x Earth's Density: 0.22 x Earth's The picture on the right uses false colors and contrast enhancement to bring out subtle details in the polar region of Uranus.

37. Uranus Uranus has a relatively featureless appearance at visible wavelengths. Even from Voyager 2 at a distance of 80,000 km there were few distinguishable features. This is believed to be due to Uranus being further from the Sun than Jupiter and Saturn, which means its temperature is lower (only 58 degrees Kelvin in the upper atmosphere). This decreases the likelihood of chemical reactions making the colorful compounds that give the surface features on Jupiter and Saturn. In addition, the upper atmosphere is thought to have a high-level petrochemical haze that obscures features lower in the atmosphere.

38. Neptune is the outermost of the four gas giants • Because of its distance from the Sun, Neptune's atmosphere is a frigid -225° C (-373° F) • Neptune, like Jupiter and Saturn but unlike Uranus, has an internal heat source and produces 2.7 times more heat than it absorbs. • The blue-green color of the planet is due to the presence of methane in the atmosphere. The atmosphere consists mostly of hydrogen, helium and methane. • Until the Voyager encounter in 1989, the rings surrounding Neptune were thought to be arcs. We now know that the rings completely circle the planet, but the thickness of each ring varies along its length.  Neptune Facts

39. Discoverer(s): Galle, Challis, Adams, & Le Verrier (1846) Spacecraft Encounter(s): Voyager 2 Mean Distance from the Sun: 30.06 AU (4.497 billion km/2.794 billion mi) Length of year: 165 years Rotation period: 16.11 hours Mean orbital velocity: 5.43 km/s (3.3 mi/s) Diameter: 49,528 km/30,775 mi Inclination of axis: 29.6° Number of observed satellites: 8 Comparisons with Earth: Diameter: 3.883 x Earth's Average distance from Sun: 30.06 x Earth's Mass: 17.14 x Earth's Density: 0.31 x Earth's Neptune Facts

40. Neptune has a great storm in the southern hemisphere called the “Great Dark Spot" that is about half the size of Jupiter's Great Red Spot and so is roughly the same diameter as the Earth, and at least one other smaller storm spot has been detected as well. • Like the other gas giants, there are rapid winds confined to bands of latitude, including one band that is moving the Great Dark Spot westward at over 1,100 km (or 700 miles) per hour. Indeed, Neptune has the fastest planetary winds in the Solar System, reaching as fast as 2,000 km (over 1,200 miles) per hour. Neptune’s Great Dark Spot

41. Neptune’s Great Dark Spot The bright cirrus-like clouds of Neptune change rapidly, often forming and dissipating over periods of several to tens of hours. In this sequence spanning two rotations of Neptune (about 36 hours) Voyager 2 observed cloud evolution in the region around the Great Dark Spot (GDS)