15 February 2005AST 2010: Chapter 101 The Giant Planets

15 February 2005AST 2010: Chapter 102 Jupiter Saturn Uranus Neptune The Jovian Worlds

15 February 2005AST 2010: Chapter 103 Exploration  First spacecrafts: Pioneer 10 (1972) & 11 (1973) Can we navigate through the asteroid belt? What are the radiation hazards near the planets?  Pioneer 10 flew by Jupiter in 1973 and flew out the solar system  Pioneer 11 flew by Jupiter in 1974 and was deflected towards Saturn which it reached in 1979

15 February 2005AST 2010: Chapter 104 Exploration  Voyager 1 & 2 (launched 1977) Highly productive Missions Carried 11 scientific instruments including cameras and spectrometers, devices for measuring magnetospheres  Voyager 1 Reached Jupiter (1979) and Saturn (1980) Used gravity assist towards Saturn  Voyager 2 Reached Jupiter four month later than Voyager 1 Reached Saturn (1981), Uranus (1986), Neptune (1989)  Multiple Flybys possible thanks to approximate alignment of the planets Such an alignment occurs once in 175 years 2 Voyager 2

15 February 2005AST 2010: Chapter 105 Exploration  Galileo space probe Launched 1989 Reached Jupiter December 1995 Deployed a small entry probe for a direct study of Jupiter’s atmosphere Sept. 2003, probe sent into Jupiter’s atmosphere to end its mission  Cassini Launched 1997 Reached Saturn in 2004, now in orbit Deployed entry probe for Titan in Jan. 2005

Galileo Space Probe

15 February 2005AST 2010: Chapter 107 Galileo – Jupiter Entry Probe  Mass 339 kg  Plunged at shallow angle into Jupiter at speed of 50 km/s  Slowed down by friction against Jupiter atmosphere Temperature of its shield reached 15,000°C  Speed dropped to 2500 km/h  Deployed parachute for actual entry in the atmosphere  Transmitted data to orbiter, for retransmission to Earth

15 February 2005AST 2010: Chapter 108 Some Results of the Galileo Mission  The discovery of a satellite (Dactyl) of an asteroid (Ida)  Jovian wind speeds in excess of 600 km/hour (400 mph) were detected  Far less water was detected in Jupiter's atmosphere than estimated from earlier Voyager observations and from models of the Comet Shoemaker-Levy 9 impact  Far less lightning activity (about 10% of that found in an equal area on Earth) than anticipated. The individual lightning events, however, are about ten times stronger on Jupiter than the Earth  Helium abundance in Jupiter is very nearly the same as its abundance in the Sun (24% compared to 25%)  Extensive resurfacing on Io due to continuing volcanic activity since the 1979 Voyagers fly-bys  Evidence for liquid water ocean under Europa's ice

15 February 2005AST 2010: Chapter 109 Huygens Probe Dropped by Cassini Orbiter

Basic Facts of Jovian Planets  Large distances from the sun  Long periods  Jupiter and Saturn similar in composition and internal structure  Uranus and Neptune smaller and differ in composition and structure Basics Properties of the Jovian Planets Planet Distance (AU) Period (years) Diameter (km) Mass (Earth=1) Density (g/cm3) Rotation (hours) Jupiter Saturn Uranus Neptune

15 February 2005AST 2010: Chapter 1011 Appearance  Only the upper atmosphere of the giant planets is visible to us Astronomers believed that their interiors are composed primarily of hydrogen and helium  The uppermost clouds of Jupite and Saturn are composed of ammonia (NH 3 ) crystals  Neptune’s upper clouds are made of methane (CH 4 )  Uranus has no obvious clouds, only deep and featureless haze

15 February 2005AST 2010: Chapter 1012 Rotation  How does one determine the rotation rate of the giants?  For Jupiter: 1st option: use dynamic surface features (storms)  However the cloud rotation may have nothing to do with the rotation of the mantle and core… 2nd option: look at periodic variations of radio waves associated with the magnetic field produced deep inside the planet  This gave rotation period of 9 h 56 m  The same technique is used to measure the rotation of other giant planets: Saturn has 10 h 40 m Uranus and Neptune have about 17 hours

 Jupiter is tilted by 3 o No seasons to speak of  Saturn is tilted by 27 o Long seasons  Neptune is t ilted by 27 o Long seasons  Uranus is Tilted by 98 o Practically orbiting on its side Rings and satellites follow same pattern 21 year seasons!!! Why this odd tilt?  A giant impact in the past could be the cause Seasons on the Giants Seasons on Uranus

15 February 2005AST 2010: Chapter 1015 Giant Planets – Giant Pressure  Giant planets composed mainly of hydrogen (H) and helium (He)  But because of its enormous size, the H and He in the center of Jupiter are compressed enormously Estimated pressure: 100 million bars. Central density of 31 g/cm 3  Earth by contrast has 4 million bars and 17 g/cm 3 in its center  Giant Planet implies giant pressure!!

15 February 2005AST 2010: Chapter 1016 Consequences of the Pressure  Few thousand km below the surface, hydrogen is in a liquid state  Still deeper, the liquid is further compressed and begins to act like a metal On Jupiter, part of the interior is metallic hydrogen!  Saturn is less massive Most of its interior is liquid, but not metallic  Neptune and Uranus are probably too small to liquefy hydrogen

15 February 2005AST 2010: Chapter 1017 More about Composition  The planets also have a core composed of heavier materials Possibly the original rock/ice bodies that formed before gas were abundantly captured by the planets

15 February 2005AST 2010: Chapter 1018 Internal Heat Source (1)  Because of their large sizes, all the giant planets are believed to be strongly heated during their formation Jupiter was the hottest Some of the primordial heat still remains  Giant planets may also generate energy internally by slowly contracting Even a small amount of shrinkage can generate significant heat  This probably raises the temperature of the core and atmosphere above the temperature due to the Sun’s heat  Jupiter has the largest internal source of energy 4x10 17 W A cross between a planet (like earth) and a star Internal heat probably primordial heat

15 February 2005AST 2010: Chapter 1019 Magnetic Fields  All four giant planets have strong magnetic fields and associated magnetospheres  The magnetospheres are large They extend for millions of km in space  Jupiter’s field was discovered in the late 1950’s Radio waves detected from Jupiter Electrons circulating in the magnetosphere produce the radio waves by a process called synchrotron emission  Magnetic fields of Saturn, Uranus, and Neptune discovered by flyby spacecraft

15 February 2005AST 2010: Chapter 1020 Magnetospheres  Jupiter’s magnetic field is not aligned with its axis of rotation It is tipped by 10 o  Uranus and Neptune have tilts of 60 o and 55 o  Saturn’s field is perfectly aligned with its axis of rotation

15 February 2005AST 2010: Chapter 1021 Atmospheres of the Giant Planets  The part of the planets accessible to direction observation  Dramatic examples of weather patterns Storms on these planets can be larger than Earth!

15 February 2005AST 2010: Chapter 1022 Atmospheric Composition  Methane (CH4) and ammonia (NH3) were first believed to be the primary constituents of the atmospheres  We know today that hydrogen and helium are actually the dominant gases First based on far-infrared measurements by Voyager Less helium in Saturn’s atmosphere  Precipitation of helium? Energy source of Saturn? Best measurements of composition by Galileo spacecraft (1995) upon entry to atmosphere

15 February 2005AST 2010: Chapter 1023 Clouds and Atmospheric Structure  Jupiter’s clouds are spectacular in color and size Color: orange, red, brown Fast motion  Saturn is more “subdued” Clouds have nearly uniform butterscotch hue

15 February 2005AST 2010: Chapter 1024 Atmospheric Structure of the Jovian Planets

15 February 2005AST 2010: Chapter 1025 Winds and Weather  Many regions of high/low pressures Air flow between these regions sets up wind patterns distorted by the fast rotation of the planet  Wind speeds measurable by tracking cloud patterns  Differences with Earth Giant planets spin much faster than Earth  Rapid rotation smears out air circulation into horizontal (east-west) patterns parallel to the equator No solid surface  No friction or loss of energy – this is why tropical storms on Earth eventually die out… Internal heat contributes as much energy to the atmosphere as sunlight (except for Uranus)

15 February 2005AST 2010: Chapter 1026 Winds on The Giant Planets  Winds on Uranus and Neptune are rather similar to those on Jupiter and Saturn True on Uranus in spite of the 98 O tilt

15 February 2005AST 2010: Chapter 1027 Storms  Omni-present on the giant planets  Superimposed on the regular circulation patterns  Large oval-shaped high-pressure regions on both Jupiter and Neptune  Most famous: Jupiter’s Great Red Spot In the southern hemisphere 30,000 km long (when Voyager flew by) Present since first seen 300 years ago Changes in size, but never disappears From Voyager 1 in 1979

15 February 2005AST 2010: Chapter 1028 Great Red Spot  Counterclockwise rotation with rotation period of 6 days  Similar disturbances formed in the 1930s on Jupiter Smaller circles near the red spot  Cause unknown  Long-lived because of absence of ground their size  Expected lifetime: centuries

15 February 2005AST 2010: Chapter 1029 Neptune Great Dark Spot  First seen in 1989 by Voyager  About 10,000-km long  17-day period  Had disappeared (faded?) in mid 1990s  New dark spot seen in Nov Faded by 1995  Do storms form and disappear quicker on Neptune?