15 february 2005ast 2010: chapter 101 the giant planets
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15 February 2005 AST 2010: Chapter 10 1
The Giant PlanetsThe Giant Planets
15 February 2005 AST 2010: Chapter 10 2
Jupiter
Saturn
Uranus
Neptune
The Jovian Worlds
15 February 2005 AST 2010: Chapter 10 3
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 2005 AST 2010: Chapter 10 4
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
Voyager 2 2
15 February 2005 AST 2010: Chapter 10 5
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 2005 AST 2010: Chapter 10 7
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 2005 AST 2010: Chapter 10 8
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 2005 AST 2010: Chapter 10 9
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 5.2 11.9 142800 318 1.3 9.9
Saturn 9.5 29.5 120540 95 0.7 10.7
Uranus 19.2 84.1 51200 14 1.2 17.2
Neptune30.1 164.8 49500 17 1.6 16.1
15 February 2005 AST 2010: Chapter 10 11
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 (NH3) crystals Neptune’s upper clouds are made of methane
(CH4) Uranus has no obvious clouds, only deep and
featureless haze
15 February 2005 AST 2010: Chapter 10 12
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 3o
• No seasons to speak of
Saturn is tilted by 27o
• Long seasons
Neptune is tilted by 27o
• Long seasons
Uranus is Tilted by 98o
• 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 2005 AST 2010: Chapter 10 15
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/cm3
Earth by contrast has 4 million bars and 17 g/cm3 in its center
Giant Planet implies giant pressure!!
15 February 2005 AST 2010: Chapter 10 16
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 2005 AST 2010: Chapter 10 17
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 2005 AST 2010: Chapter 10 18
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• 4x1017 W
• A cross between a planet (like earth) and a star
• Internal heat probably primordial heat
15 February 2005 AST 2010: Chapter 10 19
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 2005 AST 2010: Chapter 10 20
Magnetospheres Jupiter’s magnetic field is not aligned
with its axis of rotation •It is tipped by 10o
Uranus and Neptune have tilts of 60o and 55o
Saturn’s field is perfectly aligned with its axis of rotation
15 February 2005 AST 2010: Chapter 10 21
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 2005 AST 2010: Chapter 10 22
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 2005 AST 2010: Chapter 10 23
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 2005 AST 2010: Chapter 10 24
Atmospheric Structure of the Jovian Planets
15 February 2005 AST 2010: Chapter 10 25
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 2005 AST 2010: Chapter 10 26
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 98O tilt
15 February 2005 AST 2010: Chapter 10 27
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 2005 AST 2010: Chapter 10 28
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 2005 AST 2010: Chapter 10 29
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. 1994• Faded by 1995
Do storms form and disappear quicker on Neptune?