1	Astr 1050 Fri., Dec. 9, 2005 Today: Solar System Overview
2	Solar System topics for the exam: General properties of the planets Order, relative size, make-up (terrestrial vs. Jovian), atmosphere (including greenhouse effect) General properties of the interesting moons and ring systems (e.g., origin of our moon, Galilean Moons, Titan) Extrasolar planets (how many, how detected?) Comets, meteors, asteroids Where do they come from, what are they made of, origin of meteor showers Very basic stuff, most can be memorized, nothing too complex – basically what’s here in the slides
3	Chapter 16: Origin of the Solar System Solar Nebula Hypothesis Context for Understanding Solar System Extrasolar Planets Dust Disks, Doppler Shifts, Transits and Eclipses Survey of the Solar System Terrestrial Planets Jovian Planets Other “Stuff” including apparent patterns with application to the nebular hypothesis
4	Patterns in Motion All planets orbit in almost the same plane (ecliptic, AKA Zodiac) Almost all motion is counterclockwise as seen from the north: All planets orbit in this direction Almost all planets spin in same direction with axes more-or-less perpendicular to ecliptic Regular moons (like our own moon) orbit in this direction, too Planets are regularly spaced steps increasing as we go outward
5	Solar Nebula Model Planets form from disk of gas surrounding the young sun Disk formation expected given angular momentum in collapsing cloud Naturally explains the regular (counterclockwise) motion Makes additional explicit predictions Should expect planets as a regular part of the star formation process Should see trends in composition with distance from sun Should see “fossil” evidence of early steps of planet formation
6	Extra-Solar Planets Hard to see faint planet right next to very bright star Two indirect techniques available (Like a binary star system but where 2nd “star” has extremely low mass) Watch for Doppler “wobble” in position/spectrum of star Watch for “transit” of planet which slightly dims light from star About 100 planets discovered since 1996 See http://exoplanets.org/ Tend to be big (³Jupiter) and very close to star (easier to see)
7	Characteristics of “Planets” Two types of planets Terrestrial Planets: small, rocky material: inner solar system Jovian Planets: large, H, He gas outer solar system Small left-over material provides “fossil” record of early conditions Asteroids – mostly between orbits of Mars and Jupiter Comets – mostly in outermost part of solar system Meteorites – material which falls to earth
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9	Evidence of Assembly Process? Craters
10	Craters evident on almost all small “planets”
11	Chapter 17: Terrestrial Planets Earth History, Interior, Crust, Atmosphere The Moon In particular origin Mercury Venus Mars Including water (and life ?)
12	“Comparative Planetology” Basis for comparisons is Earth Properties of Earth Similarities and differences with Mars and Venus help us understand Earth better (e.g., life, greenhouse effect, etc.) Won’t spend class time on basic properties (size, gravity, orbital period, length of day, number of moons, etc.) but you should have some relative ideas about these (see “Data Files” in text).
13	Timeline
14	Earth’s Atmosphere: Greenhouse Effect
15	The Moon and Mercury No atmosphere Cratering is evidence of final planet assembly – lots to be learned from craters
16	Examples of craters on the moon Images on line at The Lunar and Planetary Institute: http://www.lpi.usra.edu/expmoon/lunar_missions.html Detailed record of Apollo work at: http://www.hq.nasa.gov/office/pao/History/alsj/frame.html
17	Effects of late impacts
18	Moon: Giant Impact Hypothesis Explains lack of large iron core Explains lack of “volatile” elements Explains why moon looks a lot like earth’s mantle, minus the volatiles Explains large angular momentum in the earth-moon system
19	Venus
20	Expect Venus to be similar to Earth? (It isn’t!) Venus only slightly closer to sun, so expect about same initial composition Venus only slightly smaller than Earth, so expect about same heat flow Venus atmosphere is dramatically different Very thick CO₂ atmosphere Virtually no water in atmosphere or on surface Venus shows relatively recent volcanic activity, but no plate tectonics Both probably related to its slightly closer position to the sun which caused loss of its critical water Thick atmosphere and clouds block direct view so information from: Orbiting radar missions (Magellan in early 90’s) Russian landers (as in previous photo)
21	Surface Relief of Venus from Radar Venus does show evidence of “recent” volcanism It does not show linear ridges, trenches, or rigid plates In a few spots there are weak hints of this – but clearly different
22	Volcanoes Sapas Mons Lava flows from central vents Flank eruptions Summit caldera Size: 250 miles diameter 1 mile high
23	Lava Channels Large! 100’s of miles long 1.2 miles wide High Venus temperatures may allow very long flows Composition could also be different
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25	Lots of Martian Science Fiction Best, most recent and scientifically accurate is probably Kim Stanley Robinson’s series: Red Mars, Blue Mars, Green Mars Terraforming/colonization of Mars
26	Mars and the Pattern of Geologic Activity and Atmospheric Loss Expect intermediate geologic activity based on size R_Mars = 0.53 R_EarthR_Moon = 0.27 R_Earth Earth still active but lunar mare volcanism ended ~3 billion years ago Expect intermediate atmospheric loss Smaller size will make atmospheric escape easier Cooler temperature (farther from sun) will make astmospheric escape harder In some ways Mars is most “Earth-like” planet Has polar caps Has weather patterns Had (in past) running water May have had conditions necessary for development of life
27	Which planets can retain which gasses?
28	Mars atmosphere today Pressure is only ~1% of Earth’s Composition: 95% CO₂ 3% N₂ 2% Ar Water: Pressure too low for liquid water to exist Water goes directly from solid phase to gas phase CO₂ (dry ice) acts like this even at terrestrial atmospheric pressure Water seen in atmosphere Water seen in polar caps Evidence of running water in past Carbon dioxide (CO₂) Gets cold enough for even this to freeze at polar caps Unusual meteorology, as atmosphere moves from one pole to other each “year”
29	Mars dust storm
30	Sand Dunes on Mars Spacecraft in Mars orbit Mars Global Explorer Mars Odyssey Even though atmosphere is thin, high winds can create dust storms
31	Water ice clouds
32	Ancient River Channels? (note channels older than some craters – by superposition)
33	Recent liquid water? (water seeping out of underground “aquifer” ?)
34	Layered Deposits
35	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)
36	Jovian Planets
37	Ice+Rock Core H+He “Atmosphere”
38	Jupiter as seen by Cassini
39	Aurora on Jupiter
40	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
41	Saturn as seen by the Hubble Space Telescope
42	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
43	Comparison of Rings All within Roche limit Details controlled by Resonances and Shepard Satellites
44	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, volcanic activity Outer two (Ganymede, Callisto) more icy
45	Io, Europa break rules about activity Io most volcanically active body in solar system Europa shows new icy surface with few craters
46	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
47	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
48	Comparison of Satellites
49	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 dropped a probe in early 2005. “Code of the Lifemaker” by James P. Hogan, good sf
50	Ch. 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
51	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
52	The larger asteroids
53	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”
54	Types of Meteorites Three main kinds of meteorites Carbonaceous chondrites: Most primitive material – dark because of C Stones Similar to igneous rocks Irons Metallic iron – with peculiarities
55	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
56	Large Meteor over the Tetons (1972)
57	The Leonids 2001 APOD site: Picture by Chen Huang-Ming
58	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
59	Comets: Hale-Bopp in April 1997
60	Hale-Bopp clearly shows components
61	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
62	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
63	Pluto and Charon