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Transcript
The Planets of Our Solar System The Outer Planets Jupiter Saturn Earth Included for Scale. Uranus Pluto Neptune Orbits of the Giant Planets, Jupiter and Saturn JUPITER • 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 SPACE MISSIONS TO JUPITER • 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, respectively. • 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 environments. • 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 FAR ULTRAVIOLET SPECTRUM OF JUPITER AURORA (Lyman-α) THE GALILEAN SATELLITES OF JUPITER • 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 telescope. • 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 Io Europa Ganymede Callisto 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 • 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 TITAN • 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 Enceladus Mimas Variable Surface Crater Population Took a Big Hit! Orbits of the Outer Planets URANUS AND NEPTUNE • 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). URANUS NEPTUNE Clouds in Neptune’s Atmosphere Observed by Voyager-2 Triton TRITON • 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 Kelvin). • 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