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ASTRO 101 Principles of Astronomy Instructor: Jerome A. Orosz (rhymes with “boris”) Contact: • Telephone: 594-7118 • E-mail: [email protected] • WWW: http://mintaka.sdsu.edu/faculty/orosz/web/ • Office: Physics 241, hours T TH 3:30-5:00 Text: “Discovering the Essential Universe, Fifth Edition” by Neil F. Comins Course WWW Page http://mintaka.sdsu.edu/faculty/orosz/web/ast101_fall2012.html Note the underline: … ast101_fall2012.html … Also check out Nick Strobel’s Astronomy Notes: http://www.astronomynotes.com/ Homework/Announcements • Homework due Thursday, October 25: Question 6, Chapter 7 (What role did Charon play in enabling astronomers to determine Pluto’s mass?). • Exam 2, Thursday November 1 Next: Chapter 5 and Chapter 6: Other Planets and Moons. Comparing the Inner Planets Next: The Giant Planets The Giant Planets • The giant planets are Jupiter, Saturn, Uranus, and Neptune. The Giant Planets • The radii are between about 4 and 11 times that of Earth. • The masses are between 14 and 318 times that of Earth. The Giant Planets • The radii are between about 4 and 11 times that of Earth. • The masses are between 14 and 318 times that of Earth. • However, the densities are between 0.7 and 1.8 grams/cc, and the albedos are high. The Giant Planets • The radii are between about 4 and 11 times that of Earth. • The masses are between 14 and 318 times that of Earth. • However, the densities are between 0.7 and 1.8 grams/cc, and the albedos are high. • The planets are composed of light elements, mostly hydrogen and helium. The Gas Giants • The composition of the giant planets, especially Jupiter, is close to that of the Sun. The Gas Giants • The composition of the giant planets, especially Jupiter, is close to that of the Sun. • The internal structures of these planets is completely different from that of the Earth. The Gas Giants • The composition of the giant planets, especially Jupiter, is close to that of the Sun. • The internal structures of these planets is completely different from that of the Earth. In particular, there is no hard surface. The Gas Giants • These planets are relatively far from the Sun (more than 5 times the Earth-Sun distance), so heating by the Sun is not a big factor. Jupiter • Jupiter is by far the most massive planet in the solar system (it contains about 2/3 of the solar system mass outside the Sun). • It has the largest radius of any solar system planet, and it rotates the fastest (once every 10 hours). • It has at least 63 moons. • In many categories, Jupiter is the most extreme case. Jupiter’s Weather • Owing to its rapid rotation, Jupiter has a very turbulent atmosphere, which is composed mostly of methane and ammonia (both hydrogen rich). Jupiter’s Weather • Owing to its rapid rotation, Jupiter has a very turbulent atmosphere, which is composed mostly of methane and ammonia (both hydrogen rich). Jupiter’s Weather • Owing to its rapid rotation, Jupiter has a very turbulent atmosphere, which is composed mostly of methane and ammonia (both hydrogen rich). Jupiter’s Weather • The most famous feature on Jupiter is the Great Red Spot. The Great Red Spot • The Spot is at least 150 years old. • It is basically a giant hurricane, roughly three times the size of Earth. • Smaller features are also evident. The Great Red Spot The Great Red Spot • Similar storm systems have been observed to form recently. Jupiter’s Interior • There is no way to directly study the deep interior parts, we rely on computer models. • The interior should be hot (35,000 K), with a solid core, possibly surrounded by liquid. • The gaseous outer atmosphere surrounds molecular and liquid metallic hydrogen and helium. Jupiter’s Atmosphere • The atmosphere of Jupiter (and Saturn) consists of poisonous gas (ammonia and ammonium hydrosulfide) covering a layer of water vapor. Jupiter’s Moons • Jupiter has 4 fairly large moons, discovered by Galileo in 1610, and at least 59 other moons, all significantly smaller. Jupiter’s Moons • The largest moon is larger than Mercury. Image from Nick Strobel (http://www.astronomynotes.com) Jupiter’s Moons • The 4 Galilean moons have small rocky or iron cores. They have similar densities to our Moon, indicating that each contains a thick layer of water and ice. Io • The surface of Io is unlike that of any other solar system body. There are no impact craters, so its surface must be young. Io • There are active volcanoes on Io, the only place in the solar system outside of Earth where this is the case. Io • There are active volcanoes on Io, the only place in the solar system outside of Earth where this is the case. Volcanoes on Io • Io’s surface is constantly altered by volcanoes. Volcanoes on Io • Io’s surface is constantly altered by volcanoes. • On Earth, the energy for geological activity comes from radioactivity. Volcanoes on Io • Io’s surface is constantly altered by volcanoes. • On Earth, the energy for geological activity comes from radioactivity. • However, Io’s mass is relatively small, so it should have no radioactivity left. Volcanoes on Io • Io’s surface is constantly altered by volcanoes. • On Earth, the energy for geological activity comes from radioactivity. • However, Io’s mass is relatively small, so it should have no radioactivity left. • The heating source turns out to be Jupiter’s gravity, which compresses Io as its orbits. Europa • Europa has a very smooth surface, and it may have an ocean of liquid water underneath the surface. Europa • Europa has a very smooth surface, and it may have an ocean of liquid water underneath the surface. • Could there be primitive life? Other Jovian Satellites • The rest of Jupiter’s moons are small and have an irregular shape. • These may be fragments of a once larger body or captured asteroids. Jupiter’s Rings • Jupiter also has dark rings, discovered by Voyager in the late 1970s. Next Saturn • The most obvious feature of Saturn is its large ring system, which has been known for more than 300 years. Saturn’s Atmosphere • The composition of Saturn is similar to that of Jupiter. • Saturn also rotates rapidly, once every 10 hours or so. • Saturn’s weather is like that on Jupiter, although the contrast between different bands is much less. Saturn • Note the band-like structure in the clouds. Saturn • Note the band-like structure in the clouds. Saturn • The rings are very thin, and gaps are evident, even from the ground. They consist of fragments of ice and icecovered rocks. Saturn • The rings are very thin, and gaps are evident, even from the ground. They consist of fragments of ice and icecovered rocks. Saturn • Small satellites can cause some of the rings to ripple or to have braided structure. Saturn • Small satellites can cause some of the rings to ripple or to have braided structure. Saturn’s Rings • From Voyager, we know the rings are composed of hundreds or thousands of “ringlets”. Saturn’s Moons • Saturn has 1 very large moon (Titan), 10 moderate size moons, and a few dozen much smaller ones. Saturn’s Moons • Saturn has 1 very large moon (Titan), 10 moderate size moons, and a few dozen much smaller ones. Saturn’s Moons • Saturn has 1 very large moon (Titan), 10 moderate size moons, and a few dozen much smaller ones. • Titan is the only moon with an atmosphere. Titan • Titan’s atmosphere is mostly hydrogen with a substantial amount of methane. • There are organic molecules, but it is probably too cold for life to have evolved. Titan • There are lakes of liquid methane, as well as large flat areas. Uranus and Neptune • These distant planets were not known before the invention of the telescope. • They are each about 4 times the diameter of the Earth, and about 15 times more massive than the Earth. • They are made up mostly of H and He, but with a bit more heavy elements. Uranus and Neptune • Both planets appear blue-green because of the methane gas mixed in with the hydrogen. • The weather patterns are much less apparent. • Solar heating is not important since they are far from the Sun. Uranus and Neptune • Both planets appear blue-green because of the methane gas mixed in with the hydrogen. • The weather patterns are much less apparent. • Solar heating is not important since they are far from the Sun. Uranus and Neptune • Both planets are believed to have rocky cores surrounded by compressed water and liquid hydrogen and helium. Seasons on Uranus • The rotation axis of Uranus is inclined by about 90 degrees relative to its orbital plane. This gives rise to highly exaggerated seasons. Uranus’s Rings • Uranus also has rings, which were discovered in 1977 when Uranus passed directly in front of a distant star. • They are very dark, reflecting only about 2% of the sunlight. Uranus’s Rings • Uranus also has rings, which were discovered in 1977 when Uranus passed directly in front of a distant star. • They are very dark, reflecting only about 2% of the sunlight. Uranus’s Rings • Uranus also has rings, which were discovered in 1977 when Uranus passed directly in front of a distant star. • Recent advances in telescopes and cameras allow for a better view than was previously possible. Uranus’s Rings • Recent advances in telescopes and cameras allow for a better view than was previously possible. • Note the system of moons that orbit in the equatorial plane. They take their names from Shakespeare’s A Midsummer’s Night Dream and other works. Neptune’s Rings • Neptune also has dark rings, discovered by Voyager in the late 1980s. Rings • All of the gas giants have rings, although the rings of Saturn are by far the largest. • They appear to be relatively short-lived (only millions of years) and composed of material from moons that wandered to close to their parent planets. Neptune’s Moons • Neptune has at least 13 moons, most of which appear to be captured asteroids. The largest moon, Triton, was captured into a retrograde orbit, and will soon be destroyed by Neptune’s gravity. Next: Chapter 7 (Dwarf Planets and Small Solar System Bodies)