9Gas giants (Jovian planets) Are mostly gases (H, He, H2O, CH4, NH3); the rest = ice + rockHave no solid surface: gases --> solid at high pressureHave ring systems and many moonsForm faster, and in a different way, compared to terrestrial planets: large enough to accumulate gas directly from the solar nebulaThey are far from the Sun (in the case of the solar system)So far, all known extrasolar planets are gas giants, but they are all close to their parent star (why?)
10Jupiter, imaged with the Hubble Space TelescopeColorful cloud bands are the most striking characteristic of the planet, and the Great Red Spot
11Neptune: Its existence was predicted because Uranus did not seem to obey Kepler’s Law! Images taken by the Voyager 2 spacecraft
12The giant planets are much more massive and less dense than Earth They rotate much faster than Earth95 MEarth318 MEarth15 MEarth17 MEarthGas giants rotate differentially: rotation is faster at their equator than their poles (like which other object in the solar system??They all have magnetic fields (molten interiors)
13Belts and zones on Jupiter Differential rotation
14Jupiter’s most distinguishing features: The Great Red SpotCloud bandsthe “Galilean moons”Storms on gas giants last so long because there are no continents over which they can lose their energy and dissipate
15What causes Jupiter’s cloud bands? Strong winds and Jupiter’s differential rotation produce bands parallel to equatorhydrogen, helium, water (H2O), ammonia (NH3) and methane (CH4)These gases are colorless, and their ices are whiteColors due to sulfur compounds and organic hazes particles (?)Sunlight and lightning affect the chemistry of Jupiter’s atmosphere
16Clouds and convection in Jupiter’s atmosphere Zones: high pressure, lighterBelts: Lower pressure,darker colorRotation channels the winds into east-west pattern that wraps around entire planetZonal flow: stable eastward and westward winds deeper in the atmosphere300 km/hour easterly, at equator0 at poles - bands disappear
17Entry site of Galileo Probe: the first man-made object to enter the atmosphere of a giant planet
18Saturn is not as colorful as Jupiter, but does have bands and storms Saturn has less hydrogen and helium than Jupiter, and the ratio of helium to hydrogen is much lower: why?Helium seems to have liquified and sank to Saturn’s centerHelium precipitation seems to be the cause of Saturn’s energy output
19color enhancedLike Jupiter, Saturn has:bandsoval storm systemsturbulent flow patternsstable east–west zonal flowwind speed is > Jupiter with fewer east–west alternations.The equatorial eastward jet stream = 1500 km/h
20Storms on Saturn are more rare than on Jupiter In 1990, a storm developed in Saturn’s equatorial region and soon completely encircled the planet.The storm dissipated in a few weeks.
21UranusNeptuneBoth worlds are composed mostly of hydrogen and heliumAmmonia is in the form of ice crystals (snow), not as a gasMethane gives these planets their blue color : absorbs red and yellow photons from sunlight, reflects blueNeptune has more methane than Uranus
22Does not have distinct atmospheric features (storms, bands, etc Does not have distinct atmospheric features (storms, bands, etc.) the way Jupiter doesNo high-altitude clouds; deeper features are obscured by haze layerClouds move around planet in same direction as rotation ( km/hour)colder than Jupiter & Saturn (53 K)has a thin ringUranuscomputer enhanced
23Uranus’ axial tilt is 98o -- compared to Earth’s 23o tilt New hypothesis of Uranus and Neptune formation: they originally formed between Jupiter and Saturn (5-9 AU) and migrated outward!
24NeptuneSlightly warmer than Uranus even though further from Suntemperature = 59 KHaze layer not as thickHas more obvious features than Uranus: storms, spots, bandsslightly more massive than Uranus2000 km/hour winds -- much faster than UranusThe Great Dark Spot lasted only a few years
25Using a telescope with a spectrometer, we can observe the wavelength at which Neptune radiates most of its photons. From Wien’s law,max =0.29TcmNeptune, max = cm, so Neptune’s temperature = 59 Kif it were only heated by the Sun, Neptune should be 50 K.Neptune has an internal source of energy: unknown at this time!
26Neptune’s Great dark Spot, discovered by Voyager 2 in 1989 Neptune, imaged by the Hubble Space TelescopeGreat Dark Spot is gone by 1994Atmospheric structure changes over just a few days’ time
27Computer-enhanced images of Neptune from Hubble Space Telescope Seasons are changing!
28Laws of physics and chemistry + observations = model for giant planets
29All 4 giant planets have about the same mass rocky core (10 Mearth) J & S have much more hydrogen & helium than U & NJ & S have metallic hydrogenJ & S & N radiate away more energy than they receive from Sun
30Aurorae on earth: Interaction of solar wind with Earth’s magnetic field
31The Earth has the properties of a big magnet Solar wind (charged particles) respond to this magnetic field
32The giant planets all have magnetic fields, & atmospheres, so we expect them to have aurorae too!
34Jupiter’s magnetosphere is affected by the solar wind We can measure the strength of J’s magnetic field : much stronger than Earth’s
35Formation of the gas giant planets: Gas giants form via core accretion followed by accumulating H and He gases from the solar nebula.In the solar nebula, ice was an abundant core-building material > 5 AU from the Sun, because temperatures drops as you go further from the Sun
36Gas giants must form before the solar nebula dissipates (< 10 million years) Disks are seen around many young stars