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REMINDERS: • Homework #1 due Thursday (day after tomorrow!) at the beginning of class (10:30 AM) • Homework • Office Tuesday, July 15, 2014 #2 will be available after class tomorrow (noon) Hours today will be 2-3 PM in Watanabe 401 UNDERSTANDING ORBITS • https://kerbalspaceprogram.com/ Tuesday, July 15, 2014 PLANETS AND SOLAR SYSTEM DEBRIS Tuesday, July 15, 2014 OPINION POLL! • Do you think Pluto is (or should be) a planet? • (A) Yes! How could you kill Pluto, you heartless monster? Tuesday, July 15, 2014 • (B) No, of course not, don’t be silly. • (C) I really don’t know. Maybe? • (D) Depends on how you define ‘planet.’ THE 8 PLANETS • In order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune • Usually grouped based on size and composition Tuesday, July 15, 2014 DEBRIS: ASTEROIDS, COMETS, AND DWARF PLANETS • Everywhere in the solar system: billions of objects • Sizes varying from a few meters to 1000s of km across • Mostly composed of rocks, dust, and ice • Similar to the building blocks for planets Tuesday, July 15, 2014 THE SHAPE OF THE SOLAR SYSTEM • Mostly flattened into a disk shape • The plane of this disk is called the ecliptic • An orbit’s angle to the ecliptic is called the inclination Tuesday, July 15, 2014 ROTATION IN THE SOLAR SYSTEM • Most objects rotate in the same direction around the Sun • Most planets (but not all!) spin in the exact same direction • This is a consequence of the planet formation process • Planet spin (spin, not the orbital rotation) is determined by the history of the planet Tuesday, July 15, 2014 Tuesday, July 15, 2014 WHAT MAKES SOMETHING A PLANET? • IAU official definition: • 1) Orbits the sun • 2) Has enough mass to pull itself into a spherical shape • 3) Has ‘cleared the neighborhood’ around its orbit Tuesday, July 15, 2014 WHAT MAKES SOMETHING A PLANET? • More intuitive requirements: • 1) Specific formation history (planetesimals + gas accretion) • 2) Smaller than a Brown Dwarf star, but big enough to be spherical • 3) Gravitationally dominates its orbital region, is by far the largest object in its orbit • 4) Tuesday, July 15, 2014 Only orbits a star (not, say, another planet) CLASS ACTION! Tuesday, July 15, 2014 TO BE A PLANET, AN OBJECT MUST MEET 3 CRITERIA • Which of these three does the moon not meet, causing it not to be classified as a planet? • (A) Only orbits the Sun • (B) Is spherical • (C) Cleared the neighborhood of other objects Tuesday, July 15, 2014 TO BE A PLANET, AN OBJECT MUST MEET 3 CRITERIA • Which of these three does the moon not meet, causing it not to be classified as a planet? • (A) Only orbits the Sun • (B) Is spherical • (C) Cleared the neighborhood of other objects Tuesday, July 15, 2014 ROCKY PLANETS • Formed as clumps of dust grains, which stick to each other and build to bigger sizes • At some point, the dust clumps stop sticking, but can start merging • Some survive to become large (100s of kilometers in size), called planetesimals • These gather smaller objects and grow into planets Tuesday, July 15, 2014 GIANT PLANETS Tuesday, July 15, 2014 • Form first, typically further out from the star • Collections of dust grains grow and stick with the help of ices • When the rocky part is big enough, it starts collecting gas • The more gas a planet collects, the more it can collect • Stops when all the gas around it is gone MERCURY • Radius: 2439 • Mass: 6.08 ×1023 kg (0.06 Earths) • Semi-major • Axial axis: 0.39 AU tilt: 2’.11 • Year: 88 Earth days • Day: 176 Tuesday, July 15, 2014 km (0.38 Earths) Earth days MERCURY FACTS • Smallest planet, but also very dense (large iron core) • No atmosphere • May still have water (frozen) at the poles, hidden in shadows • Surface similar to the far size of the Moon: craters, no geologic activity Tuesday, July 15, 2014 VENUS • Radius: 6052 • Mass: 4.87 ×1024 kg (0.82 Earths) • Semi-major • Axial km (0.95 Earths) axis: 0.72 AU tilt: 177° • Year: 225 Earth days • Day: 243 Earth days, retrograde Tuesday, July 15, 2014 VENUS • Almost a twin of Earth • Huge, dense atmosphere of CO2 (96%) and Nitrogen (3%) • Thick sulfuric acid clouds block view of surface • Evidence of ancient volcanoes on surface • Extremely hot due to greenhouse effect Tuesday, July 15, 2014 EARTH • Radius: 6371 • Mass: 5.97 ×1024 kg (1 Earths) • Semi-major • Axial axis: 1 AU tilt: 23° • Year: 365 • Day: 1 Tuesday, July 15, 2014 km (1 Earths) Earth days Earth day EARTH • One large moon • Atmosphere of Nitrogen (78%) and Oxygen (21%) • Significant surface water, possibly more inside • Only planet in universe known to support life • Very Tuesday, July 15, 2014 geologically active MARS • Radius: 3396 • Mass: 6.42 ×1023 kg (0.11 Earths) • Semi-major • Axial km (0.54 Earths) axis: 1. 66 AU tilt: 25° • Year: 780 Earth days • Day: 24.6 hours (1 day + 36 minutes) Tuesday, July 15, 2014 MARS • Two small moons • Thin atmosphere of CO2 (95%) and Nitrogen (3%) • Evidence of past water & geologic activity • Has polar ice caps and subsurface ice • Currently hosts 5 active spacecraft from Earth Tuesday, July 15, 2014 ASTEROID BELT • Millions of objects ranging in size from 1000 km to a grain of dust • Regarded as the remnants of a small failed planet • ‘Sculpted’ by Jupiter • Asteroids the gravity of are mostly rocky, some are metallic Tuesday, July 15, 2014 CERES • Largest across asteroid: 950 km • 1/3 the mass of the whole asteroid belt • Composed • May of ice and rock harbor an ocean of liquid water under its surface Tuesday, July 15, 2014 OPINION POLL! Tuesday, July 15, 2014 WHEN IT WAS DISCOVERED, CERES WAS CALLED A PLANET • Do you think it still qualifies as a planet, now that we know more about it? • (A) Yes • (B) No • (C) Yes, but a different kind of planet than the others we know Tuesday, July 15, 2014 JUPITER • Radius: 71492 km (11.2 Earths) • Mass: 1.89 ×1027 kg (317.8 Earths) • Semi-major • Axial axis: 5.2 AU tilt: 3° • Year: 11.86 • Day: 9.93 Tuesday, July 15, 2014 Earth years hours JUPITER’S MOONS • Jupiter has over 67 moons of varying size • Mostly ice/rock mixtures • May have warm, salty subsurface oceans Io Tuesday, July 15, 2014 Europa Ganymede Callisto JUPITER AND THE ASTEROIDS • Jupiter sculpts the shape of the asteroid belt, clearing out gaps at integer orbital resonances • Jupiter also has asteroids following and leading it in its orbit Tuesday, July 15, 2014 CLASS ACTION! Tuesday, July 15, 2014 THE ASTEROID BELT IS BETWEEN MARS AND JUPITER •A typical asteroid should have an orbital period of about: Tuesday, July 15, 2014 • (A) A year • (B) 50 days • (C) 5 years • (D) 50 years THE ASTEROID BELT IS BETWEEN MARS AND JUPITER •A typical asteroid should have an orbital period of about: Tuesday, July 15, 2014 • (A) A year • (B) 50 days • (C) 5 years • (D) 50 years SATURN • Radius: 60268 km (9.45 Earths) • Mass: 5.68 ×1026 kg (95.15 Earths) • Semi-major • Axial axis: 9.58 AU tilt: 27° • Year: 29.46 • Day: 10.5 Tuesday, July 15, 2014 Earth years hours Tuesday, July 15, 2014 Tuesday, July 15, 2014 SATURN’S MOONS • Saturn has 62 moons • Many are like Jupiter’s moons: ice and rock • Titan is the main exception: thick atmosphere, rocky surface Tuesday, July 15, 2014 TITAN • Larger than Mercury • Has a thick atmosphere of Nitrogen (95%) and methane (4%) • Has lakes of liquid methane on the surface • Atmospheric haze makes surface difficult to see Tuesday, July 15, 2014 RING SYSTEMS • All four of the giant planets have rings, Saturn’s are the largest • Made • May of rocks, chunks of ice, and dust have formed from bits of collided moons • Inner Tuesday, July 15, 2014 planets may once have had rings too... URANUS • Radius: 25559 • Mass: 8.68 ×1025 kg (14.54 Earths) • Semi-major • Axial axis: 19.29 AU tilt: 97° • Year: 84.32 • Day: 17.2 Tuesday, July 15, 2014 km (4.01 Earths) Earth years hours, retrograde URANUS • Composed of Hydrogen (83%), Helium (15%), and methane (2%) • Atmosphere has ammonia, water, and methane ice clouds • Highly tilted, possibly from interactions with other planets • 27 Tuesday, July 15, 2014 known moons NEPTUNE • Radius: 24764 km (3.88 Earths) • Mass: 1.02 ×1026 kg (17.15 Earths) • Semi-major • Axial axis: 30.1 AU tilt: 28° • Year: 165 Earth years • Day: 16.1 hours Tuesday, July 15, 2014 NEPTUNE • Composed of Hydrogen (80%), Helium (19%), and methane (1%) • Has • 13 ice clouds like Uranus known moons • First planet found by mathematical predictions Tuesday, July 15, 2014 COMETS • ‘Dirty dust snowballs:’ ice and • Mostly live far away from the sun, beyond Neptune • Can be perturbed and fall in towards the Sun • When they heat up, they leave behind tails of evaporated material Tuesday, July 15, 2014 COMET TAILS • Comets and dust have two tails: gas • Gas tail always points directly away from the Sun • Dust tail is left behind in the orbit path Tuesday, July 15, 2014 THE KUIPER BELT • Like the asteroid belt, but outside the orbit of Neptune • Many comets live here • Other objects like Pluto, Eris, Haumea, etc. • Mostly Tuesday, July 15, 2014 icy bodies PLUTO • Radius: 1153 km (0.18 Earths) • Mass: 1.31 ×1022 kg (0.002 Earths) • Semi-major • Axial axis: 39 AU tilt: 119° • Year: 246 Earth years • Day: 6.39 Earth days Tuesday, July 15, 2014 PLUTO • Composed mostly of Nitrogen ice with traces of methane and CO • Has at least 5 moons, one of which is 11% as massive as Pluto • Has a highly inclined (17°) and eccentric (e = 0.25) orbit • May Tuesday, July 15, 2014 have a core of ice and rock TRANS-NEPTUNIAN OBJECTS Tuesday, July 15, 2014 THE OORT CLOUD • Composed of comets of many billions • Extends to thousands of times farther from the sun than Neptune • Scattered remnants of planet formation • May be the source of longperiod comets Tuesday, July 15, 2014 THE EDGE OF THE SOLAR SYSTEM • Interstellar space ‘starts’ between 100 and 200 AU from the Sun • This region is called the heliopause and corresponds to the edge of the Sun’s dominant effect on the surrounding environment • Spacecraft Voyager 1 is reported to have crossed the boundary, is currently at ~128 AU from the Sun Tuesday, July 15, 2014 SPACE... THE FINAL FRONTIER Tuesday, July 15, 2014