Chapter 10 Worlds of Gas and Liquid- The Giant Planets 21st CENTURY ASTRONOMY Fifth EDITION Kay Palen Blumenthal
What is a storm on Saturn like?
The Giant Planets, Part 1 Jupiter, Saturn, Uranus, and Neptune are the giant planets. Jupiter and Saturn: mainly hydrogen and helium. 5.2 AU from Sun, and 9.6 AU from Sun. Called gas giants.
The Giant Planets, Part 2 Uranus and Neptune: smaller, have much more water, water ice, and other ices. 19.2 AU from Sun, and 30.0 AU from Sun. Called ice giants. Descrip@on Orbital Jupiter 5.20 Saturn 9.6 Uranus 19.2 Neptune 30 semimajor axis (AU) Orbital period (Earth years) Orbital velocity (km/s) Mass (M Earth = 1) Equatorial radius (km) Equatorial radius (R Earth = 1) 11.9 29.5 84.0 164.8 13.1 9.7 6.8 5.4 317.8 95 14.5 17.1 71,490 60,270 25,560 24,300 11.2 9.5 4.0 3.8 Oblateness 0.065 0.098 0.023 0.017 Density (water 1.33 0.69 1.27 1.64 = 1) Rota@on period (hours) 9.9 10.7 17.2 16.0 Tilt (degrees) 3.13 Surface gravity 2.53 26.7 1.07 97.8 0.89 28.3 1.14 (rela@ve to Earth's) Escape speed (km/s) 59.5 35.5 21.3 23.5
Discovery of the Giant Planets, Part 1 Jupiter and Saturn were known to the ancients. Uranus was too faint to be discerned from the other stars. Discovered in 1781 by Herschel by accident (at first thought it was a comet).
Discovery of the Giant Planets, Part 2 Neptune was found because Uranus was straying from its predicted orbit. Gravity of Neptune was tugging on Uranus. Found in 1846 by Galle after being mathematically predicted by Le Verrier and Adams.
Characteris@cs of the Giant Planets Called giant planets because of their mass from 14.5 Earth masses (Uranus) to 318 (Jupiter) and also, their physical size. No solid surfaces: We just see the cloud layers in the atmospheres.
Measuring the Giants Planetary diameters are found by observing how long it takes for a planet to pass over a star: stellar occultation. Planetary masses are found by observing the motions of a planet s moons and effects of gravity.
More Giant Characteris@cs, Part 1 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 tub of water. Jupiter s chemistry is like the Sun: mostly hydrogen and helium. Saturn has some more heavy elements, but is like Jupiter; Uranus and Neptune have much more heavy elements.
More Giant Characteris@cs, Part 2 All giants have rapid rotation and therefore different amounts of oblateness. They also have different obliquities. Jupiter: 3. Uranus: 98, which results in extreme seasons.
Cloud Pa_erns Jupiter Strong dark and light bands. A long-lasting giant storm (Great Red Spot). Many smaller storms. Colors indicate complex chemistry.
Cloud Pa_erns Saturn Saturn has a similar band structure to Jupiter, but less pronounced. It has violent storms and a feature similar to Earth s jet stream.
Cloud Pa_erns Uranus & Neptune Infrared observations let us see details of structure on Uranus. Weak banding on both Uranus and Neptune. Small, scattered bright or dark clouds. Transient large storms (Great Dark Spot on Neptune).
Under the Cloud Tops Jupiter & Saturn The gas giants have similar cloud layers. Temperature, pressure increase downward. Different heights of cloud layers. Clouds on Jupiter: Ammonia (NH 3 ) at T = 133 K; Ammonium hydrosulfide (NH 4 SH) at T = 193 K.
Under the Cloud Tops Uranus & Neptune Unlike Jupiter and Saturn, the highest clouds on Uranus and Neptune are methane ice. Bluish because of scattering by methane. Clouds on Jupiter and Saturn are colored by impurities.
Winds & Storms, Part 1 Rapid planetary rotation results in strong Coriolis forces. This causes storm rotation. Most extreme equatorial winds are in Saturn s and Neptune s atmospheres, with maximum speeds up to 2,000 km/hr.
Winds & Storms, Part 2 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 global circulation patterns.
Models of the Interior, Part 1 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 a liquid mixture of water, rock, and metals.
Models of the Interior, Part 2 Uranus and Neptune are smaller and have less pressure than the gas giants. They have more water and ices (ammonia, methane). Deep oceans containing dissolved gases and salts are present.
Magne@c Fields Magnetic fields are generated by the motion of the electrically conducting liquids. Like a bar magnet. Their orientation is at an angle to the rotation axis.
Magnetospheres Magnetospheres are huge (Jupiter s is 6 AU). They interact with the solar wind. Auroras ( northern lights on Earth). Produce strong radio waves/synchrotron radiation.
Effects of Magne@c Fields Strong magnetospheres concentrate charged particles in radiation belts, including the plasma torus created by particles from Jupiter s moon Io. Powerful flux tubes create bright auroras.
Origins Jupiter and Saturn formed from the protoplanetary accretion disk while hydrogen and helium were still present. Solar wind later blew out these gases. Uranus and Neptune formed later, by the merger of icy smaller bodies. All four possess a dense liquid core containing rocky materials. Many details are still not understood.
Planetary Migra@on Hot Jupiters are seen orbiting close to their stars in extrasolar planetary systems. Computer simulations show that the giant planets may not have formed where they exist now, but rather could have migrated to their positions due to gravitational influences.
PROCESS OF SCIENCE Theories make predictions that serve as opportunities to falsify them or strengthen confidence in the theory. These predictions are essential to scientific progress.
Check Your Understanding 10.1 Uranus and Neptune are different from Jupiter and Saturn in that: a) Uranus and Neptune have a higher percentage of ices in their interiors; b) Uranus and Neptune have more hydrogen; c) Uranus and Neptune have no magnetic field; d) Uranus and Neptune are closer to the Sun.
Check Your Understanding 10.2 Why is Jupiter reddish in color? a) because it is very hot; b) because of the composition of its atmosphere; c) because it is moving very quickly; d) because it is rusty, like Mars.
Check Your Understanding 10.3 The interiors of the giant planets are heated by gravitational contraction. We know this because: a) the cores are very hot; b) the giant planets radiate more energy than they receive from the Sun; c) the giant planets have strong magnetic fields; d) the giant planets are mostly atmosphere.
Check Your Understanding 10.4 The radiation belts around Jupiter are much stronger than those found around Earth because: a) Jupiter has larger storms than Earth; b) Jupiter is colder than Earth; c) Jupiter rotates faster than Earth; d) Jupiter has a stronger magnetic field than Earth.
Check Your Understanding 10.5 How does our Solar System differ from the other detected solar systems?
Working it Out 10.1 Measuring Wind Speeds Wind speeds on gas giants can be measured by observing the movement of clouds above an assumed surface. Using the circumference of the planet, you can find how much a spot travels in a given time.
Working it Out 10.2 Internal Thermal Energy Jupiter, Saturn, and Neptune radiate away more energy than they get from the Sun. A small increase in internal temperature leads to a large increase in emitted energy. Something has to be increasing the temperature. It is believed that the planets are still shrinking, with gravitational energy being converted into heat during that process. For Jupiter:
This concludes the Lecture PowerPoint presentation for Chapter 10 For more digital resources, please visit the student Site for 21 st Century Astronomy at digital.www.norton.com/astro5 21 st CENTURY ASTRONOMY Fifth EDITION Kay Palen Blumenthal