11.2 The Giant Planets
5 min read•june 12, 2024
The of our solar system are cosmic behemoths with unique characteristics. , , , and boast massive sizes, rapid rotations, and distinct atmospheric features that set them apart from their rocky inner planet counterparts.
These are primarily composed of hydrogen and helium, with varying amounts of heavier elements. Their internal structures, from gaseous outer layers to dense cores, play crucial roles in generating powerful magnetic fields and driving complex atmospheric dynamics.
Physical Characteristics and Internal Structure of the Giant Planets
Physical features of outer planets
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- Jupiter
- Largest planet in the solar system has a mass more than twice that of all other planets combined
- shape flattened at the poles due to rapid rotation (completes one rotation in about 10 hours)
- Banded appearance with light-colored zones and darker belts parallel to the equator caused by strong east-west winds
- a large, persistent (larger than Earth) that has existed for at least 400 years
- Rotation period approximately 10 hours, the shortest of any planet in the solar system
- Saturn
- Second-largest planet with a radius about 9 times that of Earth
- Oblate spheroid shape flattened at the poles due to rapid rotation (completes one rotation in 10.7 hours)
- Pale yellow color with faint banded appearance caused by high-altitude hazes in the atmosphere
- Prominent ring system composed of countless icy particles ranging in size from dust grains to boulders
- Rotation period approximately 10.7 hours, slightly longer than Jupiter's rotation period
- Uranus
- Third-largest planet with a radius about 4 times that of Earth
- Slightly oblate spheroid shape due to slower rotation compared to Jupiter and Saturn
- Pale blue-green color due to methane in the atmosphere absorbing red light and reflecting blue and green light
- Unique tilt of rotational axis (97.8°) causes seasons to last for decades and gives the planet a "rolling" appearance
- Rotation period approximately 17.2 hours, longer than Jupiter and Saturn but shorter than Neptune
- Neptune
- Fourth-largest planet with a radius about 3.9 times that of Earth
- Nearly spherical shape due to slower rotation and higher density compared to Jupiter and Saturn
- Deep blue color due to methane in the atmosphere absorbing red and yellow light and reflecting blue light
- Dark storm systems, such as the (an anticyclonic storm similar to Jupiter's Great Red Spot)
- Rotation period approximately 16.1 hours, slightly shorter than Uranus' rotation period
Composition of giant planets
- Composition
- Primarily hydrogen and helium the most abundant elements in the universe, making up the bulk of the giant planets' atmospheres
- Trace amounts of methane, ammonia, and water present in the atmospheres, with increasing abundance in the order of Jupiter, Saturn, Uranus, and Neptune
- Increasing proportion of heavier elements (such as carbon, nitrogen, and oxygen) from Jupiter to Neptune due to their greater distance from the Sun during formation
- Internal structure
- Gaseous outer layers composed primarily of hydrogen and helium, with increasing density and pressure with depth
- layer (Jupiter and Saturn) a highly conductive form of hydrogen that exists under extreme pressures, believed to be responsible for generating the planets' strong magnetic fields
- (Uranus and Neptune) a layer of high-pressure ices (water, methane, and ammonia) that exists beneath the gaseous outer layers
- Rocky core a relatively small, dense core composed of rock and metal at the center of each giant planet, with temperatures reaching tens of thousands of degrees Celsius
Formation and Evolution of Giant Planets
- through core accretion model
- Accumulation of rocky and icy materials to form a solid core
- Rapid accumulation of hydrogen and helium from the protoplanetary disk once the core reaches a critical mass
- Development of
- Gravitational attraction of the core pulls in surrounding gases
- Atmospheric composition reflects the composition of the protoplanetary disk at the planet's formation location
- and internal heating
- Separation of materials based on density, with heavier elements sinking towards the core
- Heat generated from gravitational contraction and radioactive decay drives and
Heat and Magnetic Fields of the Giant Planets
Internal heat in giant planets
- Sources of internal heat
- gravitational energy converted to heat during planet formation as the planet contracts under its own gravity
- Differentiation heavier elements sinking towards the core, releasing potential energy in the form of heat as they move to a lower gravitational potential
- Effects of internal heat
- Jupiter and Saturn emit more energy than they receive from the Sun due to their strong internal heat sources (about 1.7 times and 2.5 times, respectively)
- Drives atmospheric circulation and weather patterns, such as (east-west winds) and large-scale storms (Great Red Spot on Jupiter and Great White Spot on Saturn)
- Contributes to the formation of zonal winds and storms by creating temperature gradients and instabilities in the atmosphere
Magnetic fields of giant planets
- generation
- of electrically conductive material ( in Jupiter and Saturn, and possibly salty water in Uranus and Neptune) in the planet's interior generates electric currents that create a self-sustaining magnetic field
- Magnetic field characteristics
- Jupiter strongest magnetic field among the planets, with a of 10° relative to the rotational axis, and a magnetic moment about 20,000 times stronger than Earth's
- Saturn second-strongest magnetic field, nearly aligned with the rotational axis (less than 1° tilt), and a magnetic moment about 600 times stronger than Earth's
- Uranus offset and tilted magnetic field, with a 60° angle between the magnetic and rotational axes, and a magnetic moment about 50 times stronger than Earth's
- Neptune offset and tilted magnetic field, with a 47° angle between the magnetic and rotational axes, and a magnetic moment about 25 times stronger than Earth's
- Significance of magnetic fields
- Interaction with the solar wind, creating magnetospheres that protect the planets from the high-energy particles in the solar wind
- Trapping charged particles, forming radiation belts (similar to Earth's Van Allen belts) that can pose a hazard to spacecraft and potentially life
- Influencing the structure and dynamics of the planets' auroras, which are caused by charged particles from the solar wind interacting with the planets' upper atmospheres
Key Terms to Review (38)
Absorption spectrum: Absorption spectrum is a graph or display showing the absorption of light at different wavelengths by a material. It reveals the specific wavelengths absorbed by atoms or molecules, corresponding to their energy levels.
Anticyclonic Storm: An anticyclonic storm is a large-scale weather system characterized by high pressure at its center, causing air to rotate in a clockwise direction in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. This type of storm system is associated with generally fair weather and the absence of precipitation.
Atmospheric Bands: Atmospheric bands refer to the distinct patterns of absorption and emission lines observed in the spectra of planetary atmospheres. These bands provide valuable information about the chemical composition and structure of the atmosphere.
Atmospheric Circulation: Atmospheric circulation refers to the large-scale movement of air masses within the Earth's atmosphere. It is a fundamental aspect of the climate system, driving the distribution of temperature, precipitation, and other weather patterns across the planet.
Cassini Division: The Cassini Division is a prominent gap in Saturn's ring system, located between the main A and B rings. It is named after the Italian astronomer Giovanni Cassini, who first observed and described this feature in 1675. The Cassini Division is a significant and well-defined structure within the ring system, and its study provides valuable insights into the formation and evolution of planetary rings.
Cassini-Huygens: Cassini-Huygens is a joint space mission between NASA, the European Space Agency, and the Italian Space Agency to study the planet Saturn and its moons, particularly Titan. The mission consisted of an orbiter, Cassini, and a lander, Huygens, which was designed to study the atmosphere and surface of Saturn's largest moon, Titan.
Convection: Convection is the process of heat transfer through the movement of fluid (liquid or gas) caused by molecular motion. It plays a critical role in various natural phenomena, including the dynamics of Earth's crust and the energy transport within the Sun.
Convection: Convection is the transfer of heat by the movement of a fluid, such as air or water. It is a fundamental process that drives many important phenomena in Earth's crust, atmosphere, and the atmospheres of the giant planets.
Differentiation: Differentiation is the process by which a previously uniform structure or organism becomes specialized and diversified, often in the context of planetary and solar system formation. It involves the separation and development of distinct components or layers within a system, leading to increased complexity and specialization.
Dipole Tilt: The dipole tilt refers to the angle between a planet's magnetic field axis and its axis of rotation. This misalignment between the magnetic and rotational axes is a characteristic feature of the giant planets in our solar system.
Dynamo Effect: The dynamo effect is a mechanism that generates and maintains the magnetic fields of planets, stars, and other celestial bodies. It involves the interaction between a conducting fluid, such as a planet's molten metallic core or a star's plasma, and its rotation to produce a self-sustaining magnetic field through electromagnetic induction.
Earth’s magnetosphere: Earth's magnetosphere is the region of space surrounding Earth that is controlled by its magnetic field. It protects the planet from solar and cosmic particle radiation and influences atmospheric phenomena.
Europa: Europa is one of the four major moons of Jupiter, known for its icy surface and potential subsurface ocean. This intriguing celestial body has captured the attention of astronomers and astrobiologists alike, as it is considered a prime candidate for the search for extraterrestrial life within our solar system.
Gas Giants: Gas giants are the largest planets in our solar system, characterized by their massive size, predominantly gaseous composition, and unique atmospheric features. These planets play a crucial role in understanding the formation and evolution of our solar system, as described in the topics 10.1 The Nearest Planets: An Overview, 10.6 Divergent Planetary Evolution, 11.1 Exploring the Outer Planets, 11.2 The Giant Planets, and 14.3 Formation of the Solar System.
Giant planets: Giant planets, also known as Jovian planets, are large celestial bodies in our solar system characterized by their substantial size and gaseous composition. They include Jupiter, Saturn, Uranus, and Neptune.
Great Dark Spot: The Great Dark Spot was a large, dark storm system observed in the atmosphere of Neptune by the Voyager 2 spacecraft in 1989. This prominent feature was akin to the Great Red Spot seen on Jupiter, and provided valuable insights into the dynamic weather patterns of the gas giant planets.
Great Red Spot: The Great Red Spot is a massive, persistent anticyclonic storm located in the southern hemisphere of the planet Jupiter. It is one of the most distinctive features in the solar system and has been observed for centuries, providing insights into the composition, structure, and atmospheric dynamics of the giant planet.
Hydrogen-Helium Atmosphere: A hydrogen-helium atmosphere refers to the dominant gaseous composition that makes up the atmospheres of the giant planets in our solar system, including Jupiter, Saturn, Uranus, and Neptune. This atmospheric composition is characterized by the overwhelming presence of hydrogen and helium, the two lightest and most abundant elements in the universe.
Ice Giants: The ice giants are the two outermost planets in our solar system, Uranus and Neptune. These planets are characterized by their large size, low density, and composition primarily of ice, rock, and methane. The ice giants are distinct from the gas giants, Jupiter and Saturn, in their physical properties and formation history.
Icy Mantle: The icy mantle is a layer of ice that surrounds the cores of the giant planets in our solar system. This icy layer is composed of frozen volatiles, such as water, methane, and ammonia, and plays a crucial role in the structure and composition of the giant planets.
Io: Io is the innermost and most volcanically active moon of Jupiter. It is known for its dramatic volcanic activity, which is driven by tidal heating from Jupiter's powerful gravitational pull.
Jovian Mass: Jovian mass refers to the large mass of the giant planets in our solar system, also known as the Jovian planets or gas giants. These planets, including Jupiter, Saturn, Uranus, and Neptune, have significantly greater masses compared to the terrestrial planets, such as Earth, Venus, and Mars.
Juno: Juno is the name of a NASA space probe that is currently orbiting the planet Jupiter, studying the giant planet's composition, magnetic field, and atmospheric dynamics in unprecedented detail. This mission is providing valuable insights into the formation and evolution of Jupiter and the entire Solar System.
Jupiter: Jupiter is the largest planet in our solar system, a gas giant with a massive, turbulent atmosphere dominated by a giant, swirling storm known as the Great Red Spot. As the fifth planet from the Sun, Jupiter's immense size and powerful gravitational field have a profound influence on the dynamics and evolution of the entire solar system.
Kelvin-Helmholtz contraction: Kelvin-Helmholtz contraction is a process that describes the gravitational collapse and gradual shrinking of a gas cloud or protostar as it radiates away its internal thermal energy. This contraction is a crucial mechanism in the formation and evolution of stars, as well as the giant planets in our solar system.
Liquid Metallic Hydrogen: Liquid metallic hydrogen is an exotic state of matter that is predicted to exist under the extreme pressures and temperatures found in the interiors of giant planets like Jupiter and Saturn. It is a form of hydrogen where the electrons are no longer bound to individual atoms, but instead form a delocalized metallic-like state, giving the material unique physical and chemical properties.
Magnetic field: A magnetic field is a region around a magnetic material or a moving electric charge within which the force of magnetism acts. It is essential in understanding the behavior of charged particles and planetary dynamics.
Magnetosphere: The magnetosphere is the region around a planet or other celestial body where the body's magnetic field dominates and interacts with the solar wind. It acts as a protective shield, deflecting charged particles and cosmic radiation, and plays a crucial role in the planet's overall structure and environment.
Metallic Hydrogen: Metallic hydrogen is a hypothetical state of hydrogen where the electrons are delocalized, allowing them to flow freely and conduct electricity like a metal. This unique form of hydrogen is believed to exist under the extreme pressures and temperatures found in the interiors of giant planets like Jupiter and Saturn.
Neptune: Neptune is the eighth and farthest known planet from the Sun in the Solar System. It is a gas giant with a dense, blue atmosphere primarily composed of hydrogen and helium, and it is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the most distant major planet from the Sun.
Oblate Spheroid: An oblate spheroid is a three-dimensional shape that is flattened at the poles and bulges at the equator, resembling an ellipse rotated around its minor axis. This geometric form is often used to model the shape of planets, including the giant planets in our solar system.
Planetary Formation: Planetary formation is the process by which planets are believed to have originated and developed within a planetary system, such as our own Solar System. This term is central to understanding the composition, structure, and evolution of planets, as well as the overall dynamics of planetary systems.
Planetary Rings: Planetary rings are vast, flattened discs of dust, ice, and rock that orbit some planets in our solar system. These rings are found primarily around the gas giant planets, such as Saturn, Jupiter, Uranus, and Neptune, and they are a unique and fascinating feature of these celestial bodies.
Saturn: Saturn is the sixth planet from the Sun and the second-largest planet in the Solar System. It is known for its iconic ring system and diverse system of natural satellites. Saturn's unique features and characteristics make it a significant focus of study in various topics within astronomy.
Titan: Titan is the largest moon of Saturn and the second-largest moon in the Solar System. It is a unique and fascinating celestial body that has captured the attention of astronomers and space enthusiasts alike due to its intriguing features and potential for harboring life.
Triton: Triton is the largest moon of Neptune and the only major moon in the Solar System with a retrograde orbit, meaning it orbits in the opposite direction of Neptune's rotation. It is a unique and fascinating celestial body that has been studied extensively in the context of the giant planets and their ring and moon systems.
Uranus: Uranus is the seventh planet from the Sun and the third-largest planet in the Solar System. It is a gas giant with a distinctive blue-green color and is known for its unusual tilted axis of rotation, which causes it to essentially roll on its side as it orbits the Sun. Uranus plays a significant role in several topics covered in an introductory astronomy course, including the exploration of the outer planets, the characteristics of the giant planets, and the study of ring and moon systems.
Zonal Winds: Zonal winds are horizontal air currents that flow parallel to lines of latitude, either eastward or westward, in the atmospheres of planets. They are a key feature of the atmospheric circulation patterns on the giant planets, influencing their overall weather and climate systems.