Solar System October 5, 2006 I. Overview of the solar system Solar system includes A. Sun 1. 99.85% of system mass 2. Nuclear fusion of hydrogen into helium B. Objects in orbit around Sun 1. Inner terrestrial planets a. Mercury, Venus, Earth, Mars b. Small, stony, Little atmosphere 2. Outer gas planets a. Jupiter, Saturn, Uranus, Neptune b. Large, Gases (hydrogen and helium) and ices (methane, ammonia) 3. Dwarf planets, asteroids, comets, meteoroids a. Various compositions 1) Terrestrial material, 2) ices b. various locations and orbits 1) asteroid belt in planetary plane of orbit c. highly eccentric and inclined orbits compared to eight planets II. Composition of Solar System objects A. Gases low melting temperature: about absolute zero 1. hydrogen most abundant gas in solar system 2. helium B. Rocky and metallic material high melting temperature: +700 o C 1. silicate minerals like igneous rocks 2. pure metals and alloys mostly iron and nickel C. ices (of things besides water) intermediate melting temperature 1. Ammonia (NH 3 ) 2. Methane (CH 4 ) 3. Carbon dioxide (CO 2 ) 4. Water (H 2 O) D. Nebular cloud hypothesis of Solar System formation explains why inner planets and outer planets are different: temperatures and melting temperatures III. Planetary information A. Mercury 1.Innermost planet 2.smallest planet 4880 km diameter 3.orbit a. inclined 7 o to Sun s equator b. highly eccentric 45 million km to 70 million km c. Revolves quickly Orbital period 88 Earth days d. Rotates slowly 3 rotations in 2 orbits 1) 179 Earth days for one Mercury mean solar day Solar System Tour 2006.10.05 Page 1 of 9
2) Table 21.1 says 59 days that s a sidereal day WHAT S THAT? 4.No atmosphere but trace of hydrogen and helium 5.Surface a. cratered highlands and vast, smooth terrains b. scarps suggest crustal shortening c. Extreme temperatures 1) Cold nights (-280 F) 2) Hot days (800 F) 6. Very dense large iron core 7.Mariner 10 photo mosaic 1974 went to Venus first B. Venus 1.motion a. Orbit 225 days (text citation is in error) b. Rotation is 243 Earth days, and retrograde (turns backwards) c. Axial tilt 2 o (178 0 retrograde) 2.Similar to Earth a. Size 12000 km (c.f. 12756 km) b. Density and composition 1) 3000 km diameter iron core, 2) partly molten rocky mantle c. Location in the solar system d. Has atmosphere unlike Mars and Mercury 3.Shrouded in thick clouds a. Impenetrable by visible light b. Atmosphere is 97% carbon dioxide, 3% N 2, trace H 2 O c. Surface atmospheric pressure is 90 times that of Earth's 4.Surface a. Mapped by radar by Magellan Project b. Features 1) 80% of surface is subdued plains that are mantled by volcanic flows 2) Low density of impact craters 3) Tectonic deformation must have been active during the recent geologic past 4) Thousands of volcanic structures C. Mars 1.Called the "Red Planet" telecscopic surface close enough to view, and clear enough to see 2.Atmosphere a. 1% as dense as Earth's b. Primarily carbon dioxide 95%, 3% N 2, 1.6% Ar, trace H 2 O c. Cold polar temperatures (-193 F) d. Polar caps of water ice, covered by a thin layer of frozen carbon dioxide Solar System Tour 2006.10.05 Page 2 of 9
e. Extensive dust storms with winds up to 270 kilometers (170 miles) per hour Mariner landed in a dust storm 3.Surface a. Less-abundant impact craters b. Numerous large volcanoes largest is Mons Olympus, 75 km above mean surface (c. f. Everest, < 9 km above msl) c. Tectonically dead d. Several canyons 1) Some larger than Earth s Grand Canyon 2) Valles Marineras the largest canyon a) Almost 5000 km long b) Formed from huge faults e. "Stream drainage" patterns 1) Found in some valleys 2) No bodies of surface water on the planet 3) Possible origins a) Past rainfall b) Surface material collapses as the subsurface ice melts 4.Moons a. Two moons Phobos, Deimos b. Captured asteroids D. Jupiter 1.Largest planet, Very massive a. 2.5 more massive than combined mass of the planets, satellites, and asteroids b. If it had been ten times larger, it would have been a small star c. 1/800 mass of Sun 2.Movement a. Rapid rotation-- Slightly less than 10 hours b. Orbital period 4332 Earthdays 3.Banded appearance a. Multicolored Bands are aligned parallel to Jupiter's equator b. Generated by wind systems 1) Winds a) to 200 mi./h at top of atmosphere (cloud tops) b) measured to 400 mph inside 2) Storms a) move 7.5 degrees/day 48 days to circle planet b) Great Red Spot i. In planet's southern hemisphere ii. Counterclockwise rotating cyclonic storm iii. Persistent over centuries other storms survive a few days 4.Structure gas planet a. atmosphere 90% H 2, 10% He Solar System Tour 2006.10.05 Page 3 of 9
1) density increases into depth of atmosphere until liquid mixture 2) Surface thought to be a gigantic ocean of liquid hydrogen 3) Halfway into the interior, pressure causes liquid hydrogen to turn into liquid metallic hydrogen b. Slightly bulged equatorial region due to rapid rotation and lack of solid material c. Rocky and metallic material probably exists in a central core 5.Moons a. At least 28 moons b. Four largest moons 1) Discovered by Galileo in 1610, Called Galilean satellites a) He wanted to name them Medicean stars, after his patron Medici b) But named by Marius in 1610 for figures in Zeus s life 2) Each has its own character very distinct from one another a) Callisto i. Outermost Galilean moon ii. slightly smaller than Mercury, 1/3 Mercury s mass iii. Densely cratered most densely cratered body in solar system iv. composed 40% ice, 60% rock/iron; CO 2 atmosphere b) Europa i. Smallest Galilean moon ii. Icy surface a. is there liquid water beneath it? b. composition mostly rock (silicate minerals) iii. Many linear surface features what are these surface streaks? iv. weak magnetic field, tenuous atmosphere of oxygen c) Ganymede i. Largest Jovian satellite larger than Mercury ii. Diverse terrains a. Surface has numerous parallel grooves b. areas of craters iii. Magnetic field of its own imbedded within Jupiter s magnetic field iv. Structure inner iron +/- sulfur core, rocky mantle, ice crust d) Io i. Innermost Galilean moon slightly larger than Moon ii. Volcanically active a. heat source could be from tidal energy b. internal stresses from Jupiter, and other Galilean moons Solar System Tour 2006.10.05 Page 4 of 9
iii. Sulfurous/sodium-rich surface, iron (+/- sulfur) core, molten silica mantle iv. Sulfur dioxide atmosphere v. Magnetic field of its own imbedded within Jupiter s magnetic field c. Ring system 1) dark, composed of dust (not ice, like Saturn s) 2) continually resupplied by micrometeor impacts with Metis, Adrastea, Amalthea, Thebe (four inner moons of Jupiter) 6.Interplanetary reach of Jupiter a. huge magnetic field reaches past Saturn contains charged particles b. intense radiation belt between ring and uppermost cloudtops E. Saturn 1. Similar to Jupiter in its a. Atmosphere b. Composition c. Internal structure 2. Rings a. Most prominent feature b. Discovered by Galileo in 1610 but he didn t properly conceptualize them c. Geometry correctly inferred by Huygens in 1659 d. Complex Composed of small particles (moonlets) that orbit the planet 1) Most rings fall into one of two categories based on particle density a) Main rings contain particles from a few centimeters to several meters in diameter b) Faintest rings are composed of very fine (smoke-size) particles 2) Thought to be debris ejected from moons 3) Origin is still being debated 3. Other features a. Dynamic atmosphere 10% polar flattening, equatorially oblate b. Large cyclonic storms similar to Jupiter's Great Red Spot c. Thirty named moons 1) Titan the largest Saturnian moon larger than Mercury a) Second largest moon (after Jupiter's Ganymede) in the solar system b) Has a substantial atmosphere N 2, 6% argon, few % methane c) surface very new i. character debated: tectonic, windblown, liquid methane, volcanic Solar System Tour 2006.10.05 Page 5 of 9
ii. There is clear evidence for "precipitation, erosion, mechanical abrasion and other fluvial activity". d) composed of water ice and rocky silicates 2) Enceladus is brightest, shiniest object in solar system new ice! 3) other moons: a) some are captured asteroids, b) Phoebe has retrograde motion F. Uranus (oorainus) discovered 1781, barely visible to naked eye 1. Uranus and Neptune are nearly twins--bluish in appearance 2. composed of rock, ices, atmosphere composed of 83% H 2, 15% He, 2% methane 3. Rotates "on its side" 4. Rings similar composition to Jupiter s rings 5. Large moons have varied terrains five are 10-100x larger than the others a. 40-50% water ice, remainder is rock b. Titania, Oberon, Umbriel,, Ariel, Miranda G. Neptune 1. Dynamic atmosphere--composed of methane a. One of the windiest places in the solar system b. Great Dark Spot has recently disappeared, other in northern hemisphere has appeared c. White cirrus-like clouds above the main cloud deck 2. Eight named satellites, five others recently discovered a. Triton largest Neptune moon nearly as big as Moon 1) Orbit is opposite the direction that all the planet's travel (retrograde rotation) 2) Lowest surface temperature in the solar system (-391 F) 3) Atmosphere of mostly nitrogen with a little methane 4) Volcanic-like activity ice volcanoes 5) Composed largely of water ice, covered with layers of solid nitrogen and methane b. We know next to nothing about the other satellites of Neptune 3. Has rings like Uranus, curiously oriented magnetic field generated by?:water within planet 4. Galileo saw Neptune in 1613, but thought it was a star IV. MINOR MEMBERS OF THE SOLAR SYSTEM A. Dwarf planets 1. Pluto!! a dwarf planet: designated so over the summer a. Not visible with the unaided eye smaller than Moon, Triton, Titan, and Galilean moons b. Discovered in 1930 Solar System Tour 2006.10.05 Page 6 of 9
c. Highly elongated orbit causes it to occasionally travel inside the orbit of Neptune, where it resided from 1979 thru February 1999 1) orbits do not cross, so they will not hit one another 2) Pluto s orbit is inclined to plane of the ecliptic about 17 o 3) axis tilts over 120 o to plane of the ecliptic d. Moon (Charon) discovered in 1978 1) over half diameter of Pluto 2) orbit of Charon is at high angle to plane of the ecliptic 3) mutually synchronous orbits same sides of each always face one another 4) Charon is mostly ices, formed independently from Pluto e. Average temperature is -210 C icy surface of N 2 (98%), methane and CO 2 f. Arguments that it is comet, large asteroid, largest object of Kuiper Belt 2. Ceres largest object in the asteroid belt 3. Eris (formerly known as Xena) a. Discovered in 2003 b. Larger than Pluto, with a more eccentric orbit c. Nearly 100 times as far from Sun as Earth is B. Asteroids 1. Most lie between Mars and Jupiter, others on Jupiter s orbit, some Near Earth 2. Small bodies largest (Ceres) is about 620 miles in diameter discovered in 1801 3. Some have very eccentric orbits those not in asteroid belt 4. Many of the recent impacts on Moon and Earth were collisions with asteroids a. Meteor Crater 1) 20,000 to 50,000 years ago 2) 10 meter diameter b. Tunguska event 1908 1) large explosion above Siberia of 60 m asteroid 2) no surface crater ever found 3) what if it was made of methane ice? c. Near Misses 1) in 2004 with 30 meter asteroid (43,000 km from surface) 2) in 2002 with 70 m 461000 km (1.2 x Moon s diatance) 3) Asclepius March 29, 1989, 1000 m, 400,000 km (passed where Earth was 6 hours earlier 5. Irregular shapes 6. Composition a. 75% carbonaceous chondrite b. 17% nickel-iron silicate c. most others nickel-iron Solar System Tour 2006.10.05 Page 7 of 9
7. Origin is uncertain total mass is 1/2 of Moon C. Comets 1. Often compared to large, "dirty snowballs" 2. Composition a. Frozen gases ices of water, ammonia, methane, CO 2, CO b. Rocky and metallic materials cemented by the ices 3. Frozen gases vaporize when near the Sun a. Produces a glowing head called the coma ~ Jupiter diameter, with tiny nucleus inside b. Some may develop a tail that points away from Sun due to 1) Radiation pressure on dust 2) Solar wind pressure on ionized gases 3) this material is lost from comet forever, so reduced in size each time c. gases recondense upon leaving vicinity of Sun, so no longer spectacular 4. Origin Not well known form at great distance from Sun a. Short-period comets < 200 years 1) Probably from Kuiper belt beyond Neptune a) fairly circular orbits of these objects close to plane of other planets b) occasional collisions, perhaps perturbed orbits due to gravity of gas giants, throw Kuiper belt objects into eccentric orbits that pass close to Sun 2) Most famous short-period comet is Halley's comet a) 76 year orbital period i. tail 1 million miles long, ii. could be seen in daytime 1910 b) Potato-shaped nucleus (16 km by 8 km) fizzing, cratered per Giotto probe in 1986 3) Hale-Bopp in 1997 spectacular! a) had twin tail that spanned 1/5 of night sky 15 million miles long b) 40 km diameter nucleus b. Long-period comets 1) period perhaps > 100,000 years 2) may originate in Oort Cloud a) hypothetical region containing a combined mass of objects greater than the mass of Jupiter beyond Kuiper Belt b) in spherical shell around solar system D. Meteoroids 1. Called meteors when they enter Earth's atmosphere shooting star 2. A meteor shower occurs when Earth encounters a swarm of meteoroids associated with a comet's path Solar System Tour 2006.10.05 Page 8 of 9
3. Meteoroids are referred to as meteorites when they are found on Earth a. Types of meteorites classified by their composition 1) Irons most commonly found a) Mostly iron, 5-20% nickel b) May give an idea as to the composition of Earth's core c) Give an idea as to the age of the solar system 4.5 billion years 2) Stony most common type a) Silicate minerals with b) Inclusions of other minerals 3) Stony-irons mixtures 4) Carbonaceous chondrites Rare a) Simple amino acids b) Other organic material b. Meteor crater 1) 1.2 km across, 170 m deep 2) Significant amount of iron debris surrounding the crater c. Manicouagan, Quebec structure is 200 million years old d. Shoemaker-Levy 9 collision with Jupiter 4. origins of meteoroids a. interplanetary debris not swept up on accretion of planetary bodies b. displaced objects from asteroid belt c. remains of disintegrated comets Solar System Tour 2006.10.05 Page 9 of 9