Chapter 9 Lecture Outline Worlds of Gas and Liquid—The Giant Planets

Jupiter and Saturn: mainly hydrogen and helium. The Giant Planets Jupiter and Saturn: mainly hydrogen and helium. 5.2 AU from Sun, and 9.6 AU from Sun Called gas giants (top) NASA/JPL/University of Arizona; (bottom) NASA and E. Karkoschka (University of Arizona).

Uranus and Neptune: smaller, have much more water. The Giant Planets Uranus and Neptune: smaller, have much more water. 19.2 AU from Sun, and 30.0 AU from Sun Called ice giants (top) NASA/JPL; (bottom) NASA/JPL.

Finding the Giant Planets Jupiter and Saturn were known to the ancients. Uranus was too faint to be discerned from the other stars. Discovered in 1781 by Herschel. NASA/JPL

Finding the Giant Planets Neptune was found because Uranus was straying from its predicted orbit. Gravity of Neptune was tugging on Uranus. Found in 1846 by Galle NASA/JPL

Characteristics of the Giant Planets Called giant planets because of their mass—from 15 Earth masses (Uranus/Neptune) to 300 (Jupiter)—and also, their physical size. No solid surfaces: we just see the cloud layers in the atmospheres. NASA/JPL/Caltech.

Measuring the Giants Find diameters by observing how long it takes for a planet to pass over a star: stellar occultation. Find masses by observing the motions of a planet’s moons and effects of gravity.

More Giant Characteristics We see atmospheres (some very cloudy, some not), not surfaces. They are less dense than the terrestrial planets— in fact, Saturn would float in a large enough vat of water. Jupiter’s chemistry is like the Sun: mostly hydrogen and helium. Saturn has some more massive elements; Uranus and Neptune have much more.

More Giant Characteristics All giants have rapid rotation. They have different obliquities. Jupiter: 3°. Uranus: 98°, which results in extreme seasons. NASA, L. Sromovsky, and P. Fry (University of Wisconsin-Madison).

Cloud Patterns – Jupiter CICLOPS/NASA/JPL/University of Arizona. Strong dark and light bands. A long-lasting giant storm (Great Red Spot). Many smaller storms. Colors indicate complex chemistry.

Cloud Patterns – Saturn Similar band structure to Jupiter, but less pronounced. Has violent storms, as well as something similar to Earth’s jet stream. NASA/JPL/Space Science Institute;

Cloud Patterns – Uranus and Neptune Infrared observations let us see structure. Weak banding. Small, scattered bright or dark clouds. Transient large storms (Great Dark Spot on Neptune). NASA, L. Sromovsky, and P. Fry (University of Wisconsin-Madison).

Under the Cloud Tops: Jupiter/Saturn Temperature, pressure increase downward. Different heights of cloud layers. Clouds on Jupiter: Ammonia (NH3) at T = 133 K. Ammonium hydrosulfide (NH4SH) at T = 193 K.

Under the Clouds: Uranus/Neptune Unlike Jupiter and Saturn, the highest clouds are methane ice. Bluish because of scattering of light by the methane Jupiter and Saturn’s clouds are colored by impurities

Winds and Storms Rapid planetary rotation results in strong Coriolis forces. This imparts a rotation to storms. Most extreme winds are in Saturn’s atmosphere (1,650 km/hr).

Winds and Storms Alternating east/west winds make banded clouds on Jupiter. Circulation pattern differs from planet to planet in ways not understood.

Internal Heat All but Uranus have significant internal heat. Heat flows from the hot interior outward. Heat has a big effect on the global circulation patterns.

Internal Heat Jupiter is hotter than it would be just from sunlight. Jupiter radiates about 65% more energy than it receives from the Sun.

Models of the Interior Jupiter/Saturn: at depths of a few 1,000 km, gases are compressed so much they liquefy. At higher pressure and temperature, this liquid hydrogen can act like a metal. Cores are liquid water and rock.

Models of the Interior Uranus/Neptune: Have more water and ices (ammonia, methane). Have less pressure than the gas giants. Deep oceans containing dissolved gases and salts.

Origins Jupiter/Saturn formed from accretion disk while hydrogen/helium still present. Solar wind later blew out these gases. Uranus/Neptune formed later, by merger of icy smaller bodies. All four possess a dense core containing rocky materials. Many details are still not understood.

Magnetic Fields Magnetic fields are generated by the motion of the electrically conducting liquids. Their orientation is at an angle to the rotation axis. Like a bar magnet.

Magnetospheres Magnetospheres are huge (Jupiter’s is 6 AU). They interact with the solar wind. Auroras (“Northern lights” on the Earth). Produce strong radio waves.

Concept Quiz – Heat How do we know Jupiter has a significant amount of internal heat? It emits strong radio waves. Its atmosphere is mainly hydrogen and helium. It is hotter than expected at its distance from the Sun. Correct answer: C Explanation: Jupiter is much warmer than it would be if its only heat source was the Sun. The temperature of a planet is mainly set by its distance from the Sun (e.g., Figure 4.24). Choice A is incorrect because the radio waves are caused by synchrotron radiation from charged particles in the solar wind interacting with Jupiter’s magnetosphere. The statement in choice B is true, but irrelevant.

Concept Quiz – Composition Which two giant planets have a larger fraction of water than the other two? Jupiter and Saturn Uranus and Neptune Jupiter and Neptune Saturn and Neptune Uranus and Jupiter Correct answer: B

Concept Quiz – Density You discover a giant planet around another star. It is as big as Jupiter, but much more dense. What does the density tell you? It has less hydrogen and helium than Jupiter. It has a lower mass than Jupiter. Like Jupiter, it is probably hot inside. Correct answer: A Explanation: Hydrogen and helium are the lightest (less dense) materials. Rock and metals are more dense. Choice B is incorrect. The planet is stated to have the same size as Jupiter, but since it has a higher density it also has a higher mass. Choice C may be true, but is irrelevant to the question.

This concludes the Lecture PowerPoint presentation for Chapter 9 For more learning resources, please visit the StudySpace website for 21st Century Astronomy at http://wwnorton.com/studyspace 21st CENTURY ASTRONOMY THIRD EDITION Hester | Smith | Blumenthal | Kay | Voss ©2010 W.W. Norton & Company, Inc.