Week 4 Comets, Meteors, and Asteroids The Demise of Pluto as a Planet Extra-solar Planets Reading: Chapter 4.1, 4.2, 8.5, 8.6, 4.4 (~24 pages) TPS Question How many planets are there? a) b) c) d) 9 8 12 countless Kepler’s Laws • Orbits are elliptical. • The closer an object is in its orbit to the Sun, the faster it goes. • The square of the orbital period is proportional to the cube of its semi-major axis: P2 = a3. (P is how long it takes to make one orbit in years. a is distance in AU) An Inventory of the Solar System Early astronomers knew Moon, stars, Mercury, Venus, Mars, Jupiter, Saturn, comets, and meteors Now known: Solar system has 135 moons, one star, eight planets (added Uranus, and Neptune), asteroids, and meteoroids Terrestrial vs. Jovian Planets Inner 4 planets (terrestrial) – small and rocky Next 4 planets (Jovian) – gas giants The big planets are what you think about when you think about the Solar System. But, in reality, there is much more to our Solar System than the planets. Asteroids Chunks of rock and metal left over from the formation of the solar system Most asteroids very small (< 1 km). Four are larger than 300 km (Ceres, Pallas, Juno, Vesta). Most asteroids “live” in the asteroid belt – a region between Mars and Jupiter (2 to 3.5 AU). The Asteroid Belt • Probably not a destroyed planet. • More likely a “failed” planet. • Gravitational resonances from Jupiter would keep a planet from forming. • Even so, it would only be ½ the size of the Moon. Also Important: The Kuiper Belt • Flattened disk of solar system remnants out past Pluto • The Solar System extends well beyond Pluto Asteroids are found by looking for moving objects in still pictures Over 10,000 asteroids have been cataloged by the “Minor Planet Center” 90,000+ await confirmation There may be a billion or more asteroids All the asteroids combined would still be smaller than Pluto Asteroids are separated by millions of kilometers – nothing like the video game! Asteroids The inner solar system, showing the asteroid belt, earth-crossing asteroids, and Trojan asteroids Asteroids The inner solar system, showing the asteroid belt, earth-crossing asteroids, and Trojan asteroids Earth-crossing Asteroids Some asteroids have irregular orbits that take them across the path of Earth’s orbit. Killer Asteroids TPS Question What is this? a) b) c) d) Asteroid Meteoroid Meteor Meteorite Asteroids vs. Meteoriods Asteroids and meteoroids have rocky composition; asteroids are bigger (below) Asteroid Gaspra (above) Asteroid Ida with its moon, Dactyl (above) Asteroid Mathilde Asteroids Asteroids are large chunks of rock and metal left over from the formation of the solar system. There is no established difference in size between meteoroids and asteroids. Meteoroids • Meteoroids are small asteroids • They are up to a few meters in diameter • Most are less than 1 millimeter Meteor vs. Meteoriod vs. Meteorite Meteoroid: A small rocky object orbiting the Sun Meteor: The streak seen in the sky that is caused by a meteoroid burning up in the Earth’s atmosphere Meteorite: Any piece of a meteoroid or asteroid that makes it through the Earth’s atmosphere and hits the Earth. Meteors Meteors are the flash that you see when a meteoroid hits the Earth’s atmosphere and gets burned up. Meteorites Meteorites are pieces of meteoroids that make it through the Earth’s atmosphere without burning up. Craters The impact of a large meteor can create a significant crater. The Barringer meteor crater in Arizona: The Tunguska Event For example: An asteroid hit Siberia in 1908 and leveled a forest of trees. What Killed the Dinosaurs? The dinosaurs may have been killed by the impact of a large meteor or small asteroid The larger an impact is, the less often we expect it to occur The Universe Movie: The End of the Earth: Deep Space Threats to Our Planet (Just the first 20 minutes [first 3 chapters]). Comets “Dirty snowballs” – ice and rock mixed together Comets From the Past Comet Hyakutake Comet West Comet Kohoutek Comet Hale-Bopp Comets Comets are icy, with some rocky parts. The basic components of a comet: Nucleus – about 10 km in diameter Comet Nuclear Structure Coma – halo of vaporized material from nucleus Tails – are caused by the solar wind Comets have 2 tails – the ion tail and the dust tail. They can be as long as 1 AU. Comet tails point away from the Sun The dust tail is also influenced by the comet’s motion and tends to lag behind, making a curved tail The ion tail points is caused by very light ions stripped away from the nucleus by the solar wind. Points directly away from the Sun. The dust tail is made up of heavier dust particles, so it points partly towards the direction that the comet is coming from (but still away from the Sun). Where Do Comets Come From? There are 2 primary reservoirs of comets: • The Kuiper Belt • The Oort Cloud Comet Origins The size, shape, and orientation of cometary orbits depend on their location. Oort cloud comets rarely enter the inner solar system. Kuiper Belt The Kuiper Belt • Flattened disk of solar system remnants out past Pluto • Could be as many as 200 million comets here The Oort Cloud Spherical distribution of material even farther from the Sun than Kuiper Belt ~50,000 AU away Comets here mostly in circular orbit unless they get disturbed, then they can enter the inner solar system TPS Question The yearly Geminid meteor shower is caused by a) b) c) d) A meteroiod A meteor A comet An asteriod Meteor Showers Meteor showers occur when the Earth crosses the path of the orbit of a comet. Debris from the comet causes a shower of meteors. These happen the same time each year. They are named after the constellation that they appear to originate from. Meteor Shower Dates Meteors What is the difference between a(n) 1) Meteor 2) Meteoroid 3) Asteroid 4) Meteorite 5) Meteor showers OK, so there’s a lot of other stuff in the Solar System in addition to planets. This is where the topic of Pluto comes in. Let’s look at why Pluto was demoted. Our Nine Eight Planets Pluto Facts • Only 2x as big as its moon (Charon) • Since 1999, furthest “planet” from Sun • Highly tilted orbit around Sun All orbits but Pluto’s and Mercury’s are close to the same plane Is Pluto a Planet? If Pluto is a planet, why not 2003 UB313 (Eris)? “Dwarf Planets”: Ceres, Eris, and Pluto Old Vs. New Solar System Michael Brown TPS Question How many planets are there? a) b) c) d) 9 8 12 countless If Pluto isn’t a planet, then what’s this I hear in the news about all these new planets being discovered? Extra-Solar Planets That is, planets outside of our solar system. Many planets have been discovered in other solar systems. Currently over 175. This is one of the few that is visible. Extra-Solar Planets Most extra-solar planets are discovered through the “wobble” they create in their parent star’s orbit. Extra-Solar Planets, cont Others are discovered through the periodic dimming of the parent star’s luminosity. Extra-Solar Planet Orbits/Masses These are the orbits of most extrasolar planets discovered so far. All have masses closer to that of Jupiter than that of the Earth. Extra-solar Planets Orbits/Masses Trojan Asteroids Trojan asteroids orbit in front of and behind Jupiter. Caused by a gravitational resonance. About 500 are known.