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The Planets of Our Solar System
The Outer Planets
Earth Included for Scale.
Orbits of the Giant Planets, Jupiter and Saturn
• Jupiter, the largest planet in the solar system, is about 11 times
Earth’s diameter and 318 times Earth’s mass.
• Jupiter is similar to the Sun in composition, consisting mostly of
hydrogen and helium with only about 2% heavier elements.
• The clouds in Jupiter’s atmosphere consist of frozen ammonia
(NH3) at the levels directly visible, and exhibit detailed structure
and color variations.
• The Voyager and Galileo missions have obtained close-range
imagery of Jupiter and its satellites, and the Galileo Probe has
made the first in-situ measurements of the atmosphere, in and
below the cloud layer.
• Jupiter has a very strong magnetic field and an extensive region
of trapped charged-particle radiation.
• Four of Jupiter’s satellites, the Galilean satellites Io, Europa,
Ganymede, and Callisto, are comparable to or larger than our
Moon and Mercury in size.
Comparison of Infrared and Visible Images of Jupiter
Jupiter View from Hubble Space Telescope
• Jupiter and the other major outer planets have been visited by
several space missions, including the Pioneer 10 and 11 missions
which flew by Jupiter in 1973 and 1974 respectively, and the
Voyager 1 and 2, flying by Jupiter in March, 1979 and July, 1979,
• These missions not only obtained more detailed imagery and
spectrometry of these planets, their satellites, and their
atmospheres than possible with Earth-based instruments, but also
made measurements of their magnetic fields and charged-particle
• The most recent, and most comprehensive, mission to Jupiter and
its satellite system was the Galileo mission, launched in 1989,
which went into orbit around Jupiter in late 1995 and made detailed
studies of Jupiter and its satellites over a much longer period of
time than possible with the previous fly-by missions.
• The Galileo mission included a probe, which entered the
atmosphere of Jupiter in December, 1995 and obtained the first
direct, in-situ measurements of its atmosphere, and the first
measurements of any kind below the visible cloud layers.
Galileo Spacecraft Configuration
Galileo Deployment from Space Shuttle
Galileo Probe Measurements of the
Composition of Jupiter’s Atmosphere
Galileo Orbiter Views of Jupiter’s Atmosphere
Lightning in Jupiter’s Atmosphere, Observed by Galileo
Jupiter’s Polar Aurora, Observed by Galileo
• The four largest satellites of Jupiter, named Io, Europa,
Ganymede, and Callisto, were discovered by Galileo in the 17th
century when he first observed Jupiter with his newly-invented
• The largest of these, Ganymede, is larger than the planet
Mercury, and is the largest satellite in the solar system. Three of
the four (Io, Ganymede, and Callisto) are larger than our Moon.
• The innermost Galilean satellite, Io, has active volcanoes
(produced by tidal heating due to Jupiter’s gravity) and has
surface deposits of sulfur and frozen sulfur dioxide.
• The outer three satellites have large proportions of frozen water
(ice) in their crustal layers, and Europa has evidence for liquid
water below its ice crust surface.
The Galilean Satellites of Jupiter
Surface Features of the Galilean Satellites
Galileo Observation of Volcanic Activity on Io
Jupiter and Ganymede View from Cassini Fly-by
Jupiter’s Magnetosphere Observed by Cassini
Ion and Neutral Particle Spectrometer
Closeup Views of the Inner Magnetosphere of Jupiter
by Cassini Radio Emission by Energetic Electrons Measurements
The Magnetosphere of Jupiter
Io and Neutral Gas Torus
Europa and Neutral Gas Torus
Trapped Positive Ion Belt (Red)
ENA = Energetic Neutral Atom
X-Ray Image of Jupiter by Chandra, and
Magnetospheric Structure
• Saturn, the second largest planet, is about 9 times Earth’s
diameter and 95 times Earth’s mass.
• Saturn is very similar to Jupiter in its composition, atmosphere,
and cloud features.
• Saturn has a magnetic field, weaker than Jupiter’s but more
extensive than Earth’s.
• Saturn is unique in the solar system, with its extensive ring
system which consists mostly of ice particles.
• Saturn’s largest satellite, Titan, is the second largest in the solar
system and is the only satellite which has a dense atmosphere.
• Saturn has been studied close-up by the Voyager missions, and
is currently being studied in much more detail by the Cassini
spacecraft, in orbit around Saturn.
• Cassini also included the Huygens probe, which landed on Titan,
taking measurements of its atmosphere, and taking images of its
surface, in the process.
View of Saturn from Voyager
View of Far Side of Saturn from Voyager
• Titan, the largest satellite of Saturn, is the only satellite in
the solar system with a dense atmosphere (surface
density higher than Earth’s!).
• The atmosphere of Titan consists mostly of molecular
nitrogen (N2) with several percent of methane (CH4).
• The atmosphere of Titan contains dense clouds or fog
which prevents views of its surface in visible light.
• There may be oceans of liquid methane and ethane
(C2H6) on the surface of Titan.
• The Huygens probe, which landed on Titan, and its
mother Cassini spacecraft, currently in orbit around
Saturn, have made many new measurements and
obtained many new images of Titan, its atmosphere, and
cloud layers (in infrared, as well as visible, light).
Titan, Saturn’s Largest Satellite, as Viewed by Voyager
The Cassini-Huygens Mission to Saturn and Titan
• The Cassini spacecraft, which entered orbit around Saturn, and
its attached Huygens probe, which entered the atmosphere of
Titan and landed on its surface, constituted the first mission to
the Saturn system since the Voyager missions of the late 1970searly 1980s time period.
• The Cassini orbiter was the equivalent of the Galileo orbiter
which studied Jupiter and its satellites in the late 1990s to 2003
time period.
• Cassini entered orbit around Saturn in July, 2004.
• The Huygens probe entered the atmosphere of Titan, in
January, 2005, in a manner similar to the Galileo probe of
Jupiter’s atmosphere.
• During descent to its soft landing on the surface of Titan,
Huygens took photographs of its surroundings, both during
descent and after landing.
Saturn as Viewed by Cassini, May 2004
Storm Systems Observed on Saturn by Cassini
Storms in Saturn’s Southern Hemisphere Viewed by Cassini*
*False colors used to enhance contrast..
Closeup View of Saturn’s Rings by Cassini
Views of Titan From Cassini
Multi-Spectral Imaging of Titan by Cassini
(False Colors)
Infrared Imagery of Titan’s Atmosphere by Cassini
Titan, in Infrared Imagery by Cassini
South Polar Region
Composite Views of Atmosphere and Surface of Titan
False Color Multi-Spectral Infrared Image of Titan
Visible Color and Infrared False Color Composite Images of Titan
Rear Views of Titan and its Atmosphere by Cassini
Views of Titan from Huygens Lander
View of Titan’s Surface from Huygens Lander
• The “rocks” in the foreground are
thought to be frozen water (ice).
• Dark, smooth regions elsewhere
on the surface, observed by
Huygens before landing, appear to
be river beds and lakes of liquid
methane and/or ethane.
Cassini Closeup Views of Other Saturnian Satellites
Variable Surface Crater Population
Took a Big Hit!
Orbits of the Outer Planets
• Uranus and Neptune, the outermost large planets, are very
similar in size (about 4 times Earth’s diameter) and mass (14 and
17 times Earth’s mass, respectively).
• Both of these planets were visited by the Voyager-2 spacecraft,
in 1986 and 1989, respectively.
• The compositions of Uranus and Neptune are different from
those of Jupiter and Saturn, in that they have larger proportions
of heavier elements relative to hydrogen and helium.
• Methane in the atmospheres of Uranus and Neptune is largely
responsible for the bluish color of these planets.
• Both planets have magnetic fields, but with large tilts and
displacements from their axes of rotation.
• Neptune’s largest satellite, Triton, has a tenuous atmosphere of
nitrogen and methane, and is the coldest object yet visited in the
solar system (about 35 K).
Clouds in Neptune’s Atmosphere Observed by Voyager-2
• Triton, the largest satellite of Neptune, is somewhat
smaller than our Moon, and has a thin atmosphere.
• Triton has the distinction of being the coldest place in the
solar system yet visited by spacecraft (about 35 degrees
• Triton is also unusual in that it is the only major satellite
which revolves around its primary in the opposite direction
from the primary planet’s rotation.
• Voyager observations and measurements of Triton
revealed that its atmosphere consists mostly of nitrogen
and methane (similar to, but much thinner than, that of
Titan) and there are what appear to be volcanic eruptions
(but much colder, probably consisting of gaseous
nitrogen) from below its visible surface.
Triton, Neptune’s Largest Satellite
Neptune and Triton – Last Call of Voyager 2