Transcript Asteroids
Small Bodies in the Solar System ESS (2015-16) Small Planetary Bodies In addition to planets & moons, the solar system contains many other types of objects: including comets, asteroids, and meteoroids. Comets vs. Asteroids vs. Meteors Comet Structure Nucleus gas and dust are released and form an atmosphere around the comet called the coma Dust Tail Usually white Ion Tail (ionized gas) Usually blue Comet’s Tail A comet's tail points away from the Sun due to solar wind Tail gets longer when it is close to the Sun. Heat from the Sun melts, actually sublimates the ices from comet is mostly made of. Comet’s Orbit Two factors describe orbit Size of orbit Long-period > 200 years From Kuiper Belt or Oort Cloud Short-period < 200 years Eccentricity How “oval shaped” 0 = circle, 1 = very long oval Halley’s Comet has a high eccentricity Comet moves faster as orbits sun Comet’s Orbit Closest to sun – Perihelion Furthest from sun - Apihelion Rosetta Mission Comet Simulation Oort Cloud Where do they come from? Oort Cloud Not actually seen Theoretical explanation Billions to 2 trillion of objects Water, ammonia, methane 2000 AU (2000 x distance from sun to Earth) ~ 1 light year thick Asteroid Belt Asteroids Size Meters – 900 km (too small to be planet) Shape Irregular Larger one are more spherical Content Lighter – more rock Darker – more metal Asteroids Sometimes considered planetoids or minor planets Most located in asteroid belt (between Mars & Jupiter) > 200 asteroids larger than 60 miles (100 kilometers) in diameter. > 750,000 asteroids larger than three-fifths of a mile (1 km) in diameter and millions of smaller ones. Asteroids Ceres – largest asteroid in asteroid belt 580 miles across Considered dwarf planet Ida – has a natural satellite, 56 km long Dactyl 1.5 km Dactyl. Asteroids A large asteroid may have hit the Earth when the dinosaurs were alive – ~65 million years ago. Asteroids Eventually many will drop out of orbit maybe from a collision with another asteroid and heads toward Earth. < 10 km across, will burn up in the atmosphere. > 10 km across, will hit the surface of the planet. Hundreds of millions of years ago, collisions with asteroids more often. Over time, the # of asteroids in the path of the Earth decreased and collisions become less frequent. Meteoroids… Meteoroid - A small particle from an asteroid or comet orbiting the Sun. Meteor - A meteoroid that is observed as it burns up in the Earth's atmosphere – a shooting star. Meteorite - A meteoroid that survives its passage through the Earth's atmosphere and impacts the Earth's surface Meteoroids… Size Pebble to boulder (smaller than asteroids) Shape Irregular Content From asteroids & comets, so likely metal & rock Meteor Heats up to > 2,000˚C. Creates a streak of light called a “shooting star”. Fireballs - larger meteors -> brighter flash On average, 1/ 10 minutes, or about 6/hour Meteor Showers Usual rate = 6/hour Meteor Shower = rate may be as high as 60/hour Occur when Earth passes through the tail or debris of a comet Perseids (mid-August) Leonids (mid-November) Draconid Meteor Shower Meteorite Meteorites could be fragments from collisions involving asteroids. Most meteorites weigh only a few pounds and cause little damage. Impact craters Earth – not many, thick atmosphere Moon & Mercury – lots, no atmosphere Where to find – Antarctica White & not much snowfall, doesn’t melt Meteorites Flagstaff, Arizona 49,000 years ago Size Barringer Meteorite Crater Meteorite about 150 feet in diameter Weighed 650 pounds Energy = 2.5 million tons of dynamite Crater 4000 ft wide, 650 ft deep Speed (? From yesterday) Comets ~ 40 km/s Asteroids ~ 25 km/s, Meteors 11 – 72 km/s Our Solar System Scale Model of Solar System (p. 9) Read directions Calculate distances Color planets Obtain string/ribbon Cut out & place planets on string at appropriate distance 1 at a time, (so you don’t lose them!) clear tape probably best for this.