1	Astr 1050 Wed., Dec. 10, 2003 Today: Course Evaluations Chapter 18, Jovian Planets Chapter 19, “Debris”
2	Chapter 18: Worlds of the Outer Solar System Jupiter Condensation model Atmospheric winds Atmospheric chemistry Magnetic fields Other Jovian Planets (Saturn, Uranus, Neptune) will only cover major differences from Jupiter Satellites (i.e. Moons)
3	Jovian Planets
4	Ice+Rock Core H+He “Atmosphere”
5	Jupiter as seen by Cassini
6	Winds near the Great Red Spot
7	Hurricanes exist because Low Pressure trying to turn winds to the left almost balance Coriolis Force trying to turn winds to the right.
8	Jupiter has multiple cloud decks as air rises in low pressure “zones” Mostly made of H, He Trace amounts of C, N, O, S CH₄ present as gas NH₃, NH₄SH, H₂O can condense in colder upper regions Þ clouds Colors from unknown trace chemicals
9	Magnetic fields and trapped particles
10	Aurora on Jupiter
11	Jupiter as a miniature solar system Four large moons (Io, Europa, Ganymede, Callisto) Regular (equatorial, circular) orbits Pattern of changing density and composition with distance Inner two (Io, Europa) mostly rocky Outer two (Ganymede, Callisto) more icy
12	Io, Europa break rules about activity Io most volcanically active body in solar system Europa shows new icy surface with few craters
13	Tidal heating explains activity Large tides from Jupiter flex satellites Friction from flexing heats interiors Important for Io, Europa, some other outer solar system satellites
14	Possible H₂O ocean on Europa Tidal heating may keep H₂O liquid under ice cover Perhaps a location where life could evolve “Europa Orbiter” Mission being planned to determine if ocean exists
15	Callisto not active
16	Comparison of Satellites
17	Saturn as seen by the Hubble Space Telescope
18	Titan Largest moon of Saturn Has thick atmosphere Pressure ~ 1 earth atmosphere Mostly N₂, some CH₄ Gas held because of low T UV acting on CH₄ Þ smog Ethane produced – Lakes? Can “see” surface only in IR Cassini will drop probe in Fall 2004 “Code of the Lifemaker” by James P. Hogan, good sf
19	Rings are individual particles all orbiting separately Each particle – dust to golf ball to boulder size – is really a separate moon on its own orbit Orbit with Keplerian velocities: high in close, slow farther out Nearby relative velocities are low – so particles just gently bump into each other – slowly grinding themselves up Structure in rings largely caused by gravity of moons
20	The Roche Limit When can tides tear a moon apart? As a planetary body get close to another object, tidal forces distort the body more and more. Remember, Earth raises tides on the Moon just like it raises tides on the Earth If the distortion gets large enough, the moon will be pulled apart Happens at “Roche Limit” when moon is ~2.44 ´ radius of planet away At that point, tidal force pulling up on surface of moon is greater than moon’s gravity pulling down Only matters for objects held together by gravity Astronaut in orbit will not be pulled apart Is held together by much stronger chemical forces Astronaut standing on the outside of the shuttle, hoping the shuttle’s gravity would hold her there, will be pulled away from the shuttle
21	Comparison of Rings All within Roche limit Details controlled by Resonances and Shepard Satellites
22	Comparison of Jovian Planets Variation in distance presumably ultimate causes other effects P: Kepler’s third law T: Falloff mostly just result of falling solar energy But Neptune hotter because more internal heat M: Clue to details of solar nebula mode Less material in outer solar system – or perhaps less efficient capture r: Should drop with mass because less compression Works for Saturn vs. Jupiter Increase for Uranus, Neptune indicates less H, He and more heavy material
23	Chapter 19: Meteorites, Asteroids, Comets Small bodies are not geologically active They provide “fossil” record of early solar system Asteroids Mostly from region between Mars and Jupiter Left over small debris from accretion, never assembled into a large planet Meteorites come mostly from asteroids Comets “Stored” on large elliptical orbits beyond planets Thought to be “planetesimals” from Jovian planet region, almost ejected from solar system in its early history Meteorites provide only samples besides Apollo With sample in hand, can perform very detailed analysis: detailed chemistry; radioisotope age; other isotope info
24	Asteroids Most located between Mars and Jupiter Largest is Ceres 1/3 diameter of moon Most much smaller >8,000 known Total mass << Earth A few make it to earth source of the meteorites
25	The larger asteroids
26	Are Asteroids Primitive? Ida (56 km diam.) and its moon Dactyl (1.5 km diam.) Colors have been “stretched” to show subtle differences Imaged by Galileo on its way out to Jupiter
27	Phobos & Deimos: Two “misplaced” asteroids? Phobos and Diemos are small (~25 km and ~15 km diam.) moons of Mars Look like captured asteroids rather than moons formed in place Are “C” class – i.e. dark “Carbonaceous” type “asteroids”
28	Meteors vs. Meteorites Meteor is seen as streak in sky Meteorite is a rock on the ground Meteoroid is a rock in space Meteor showers (related to comet orbits) rarely produce meteorites Apparently most comet debris is small and doesn’t survive reentry Meteorites can be “finds” or “falls” For a fall – descent actually observed and sometimes orbit computed Most have orbits with aphelion in asteroid belt
29	Large Meteor over the Tetons (1972)
30	The Leonids 2001 APOD site: Picture by Chen Huang-Ming
31	Meteor Showers and Comets Meteor showers caused by large amount of small debris spread out along comet orbits Almost none makes it to the ground – no meteorites Occur each year as earth passes through orbit of comet Appears to come from “radiant point” in sky Leonids: Mid November
32	Comets: Hale-Bopp in April 1997
33	Comet characteristics Most on long elliptical orbits Short period comets – go to outer solar system “Jupiter family” still ~ in plane of ecliptic “Halley family” are highly inclined to ecliptic Longer period ones go out thousands of AU Most of these are highly inclined to ecliptic Become active only in inner solar system Made of volatile ices and dust Sun heats and vaporizes ice, releasing dust “Dirty snowball” model
34	Comet structure Gas sublimates from nucleus Dense coma surrounds nucleus Ion tail is ionized gas points directly away from sun shows emission spectrum ions swept up in solar wind Dust tail curves slightly outward from orbit shows reflected sunlight solar radiation pressure gently pushes dust out of orbit
35	Hale-Bopp clearly shows components
36	Where do comets come from? Long period comets: The Oort Cloud Most (original) orbits have aphelions of >1000 AU Need ~6 trillion comets out there to produce number seen in here Total mass of 38 M_Earth Passing stars deflect comets in from the cloud
37	Importance of comets Evidence of solar nebula Source of H₂O and CO₂ for earth Impacts continue Impacts on Earth Extinction of the dinosaurs SL-9 impact on Jupiter
38	Chapter 16-19 Review Solar Nebula Terrestrial Planets Properties of Earth Greenhouse Effect (cf. Venus, Mars) Cratering, origin of moon Jovian Planets Properties of Jupiter, composition, atmosphere Moons and Rings “Debris” Asteroids and Comets
39	Chapter 16-19 Review We’ve covered this material fast – exam will not cover subtle concepts or obscure facts. Very basic information and only the most fundamental ideas. Things you should know include: Order of planets in solar system, general sizes of orbits, sizes and compositions of the planets (also asteroids and comets in general, notable moons). How these items fit into the solar nebula picture.
40	Chapter 16-19 Review Example questions: True/False: Jupiter was probably influential in preventing the formation of a planet at the location of the asteroid belt. The dirty snowball theory suggests that the head of a comet is composed of ices. Jupiter radiates more heat than it absorbs from the sun. Venus is very hot because its atmosphere is rich in CO₂. The Greenhouse effect occurs because gases like carbon monoxide are opaque to IR radiation. The Jovian planets have lower densities than the terrestrial planets.
41	Chapter 16-19 Review Example questions: True/False: Meteorites appear to be composed of material similar to that found in comets. Jupiter’s interior is mostly liquid helium. Saturn’s rings are composed of metallic dust grains. Flow channels on Venus suggest it was once rich in water. The oxygen in Earth’s atmosphere was outgassed by volcanic explosions. Mars is the third rock from the sun.
42	Chapter 16-19 Review Example questions: Multiple choice: On a photograph of the moon, the moon measures 30 cm in diameter and a small crater measures 0.2 cm. The moon’s physical diameter is 1738 km. What is the physical diameter of the small crater? About 1738 km About 12 km About 520 km About 350 km About 3.5 km
43	Chapter 16-19 Review Example questions: Multiple choice: Though Titan is small, it is able to retain an atmosphere because? It is very cold. It is very dense. It rotates very slowly. It attracts gas from the solar wind. It has a very strong magnetic field.
44	Exam #4 20 Multiple Choice questions, 10 true/false, 1 or 2 essay/written questions, plus 1 follow-up extra credit problem (computational and meant to be challenging). About 1/2 of the questions covering the solar system About 1/2 of the questions covering Chapters 12 and 13 Questions mostly cover the basics and are not intended to be subtle or tricky.
45	Exam #4 List of possible topics for essay questions: Dark Matter Cosmic Microwave Background Radiation Extrasolar Planets Comparative Planetology of Venus, Earth, and Mars