Section 5: Comets, Asteroids, and Meteors Comets • The word "comet" comes from the Greek word for "hair.” • Our ancestors thought comets were stars with what looked like flowing hair trailing behind. Comets: “Dirty Snowballs” • Comets are loose collections of ice, dust, and small rocky particles whose orbits are usually very long, narrow ellipses. Structure of a Comet A Comet’s Head – Outer layer= Coma (water vapor, CO2, and other gases) – Solid inner core= Nucleus (frozen ice, gas and dust ) Comet’s Tail • As a comet approaches the sun and heats up, some of its gas and dust stream outward, forming a tail. • Most comets have 2 tails: – gas (ion), tail – dust tail • Tails point away from the sun because of the force of the solar wind. • A comet’s tail can be more than 100 million kilometers long. Comet’s Tail Comet’s Orbit • Comets move in an elliptical shaped orbit. Origin of Comets • Most comets are found in 2 regions of the solar system: Kuiper belt and Oort cloud. • Kuiper belt-doughnut-shaped region that extends beyond Neptune’s orbit to about 100 times Earth’s distance from the sun. • Oort cloud-spherical region of comets that surrounds the solar system out to more than 1,000 times the distance between Pluto and the sun. Famous Comets • Comet Halley is perhaps the most famous comet in history. • Each time this comet's orbit approaches the Sun, its 15-km (9-mile) nucleus sheds about 6 m (7 yards) of ice and rock into space. This debris forms an orbiting trail that, when falling to Earth, is called the Orionids meteor shower. • Halley’s comet reappears every 76 years. Its next appearance is in 2061. Comet Hale-Bopp • July 23, 1995- an unusually large and bright comet was seen outside of Jupiter's orbit by Alan Hale of New Mexico and Thomas Bopp of Arizona. • Exceptionally large size. • It was visible even through bright city skies, and may have been the most viewed comet in recorded history. • It will not appear again for another 2,400 years. Other Famous Comets • Comet Hyakutake-On January 30, 1996, Yuji Hyakutake (pronounced "hyah-koo-tah-kay"), an amateur astronomer from southern Japan, discovered a new comet using a pair of binoculars. • Comet Shoemaker-Levy 9-Between July 16 and July 22, 1994, more than 20 fragments of Comet Shoemaker-Levy 9 collided with the planet Jupiter. Astronomers Carolyn and Eugene Shoemaker and David Levy discovered the comet in 1993. It was the first collision of two Solar System bodies ever to be recorded. Comet Exploration • The Deep Impact spacecraft was launched in December 2004 and encountered comet Tempel 1 on July 4, 2005-mission that studied and impacted comet Tempel 1. • http://spaceplace.jpl.nasa.gov/en/kids/deepi mpact/index.shtml#air • Click on image in center of page to see animation Asteroids • A small and rocky space object. • Most asteroids are found in the asteroid belt. • The asteroid belt is located between the orbits of Mars and Jupiter. How many asteroids are there? • There are about 40,000 known asteroids that are over 0.5 miles (1 km) in diameter in the asteroid belt About 3,000 asteroids have been cataloged. • There are many smaller asteroids (100,000). • Asteroids are made of metals, silicate, iron, nickel, and carbon. • The first one discovered (and the biggest) is named Ceres; it was discovered in 1801. • Asteroids range in size from tiny pebbles to about 578 miles (930 kilometers) in diameter (Ceres). ASTEROIDS BECOMING MOONS • Asteroids can be pulled out of their solar orbit by the gravitational pull of a planet. They would then orbit that planet instead of orbiting the Sun. • Astronomers theorize that the two moons of Mars, Phobos and Deimos, are captured asteroids. Asteroid Strike • Scientists hypothesize that one or more large asteroids hit Earth 65 million years ago and caused extinction of the dinosaurs. • Scientists also hypothesize that the largest mass extinction, 250 million years ago, killing off 90% of all species was also caused by a large asteroid. Asteroid Exploration • Near Earth Asteroid Rendezvous- (NEAR) mission is the first of NASA's Discovery missions and the first mission ever to go into orbit around an asteroid (launched 1996). • Studies were made of the asteroid Eros’ size, shape, mass, magnetic field, composition, and surface and internal structure (last data signals sent in 2001) Meteoroids • Meteoroid-chunk of rock or dust in space. • Meteoroids come from comets or asteroids. Meteor • When a meteoroid enters Earth’s atmosphere, friction with the air creates heat and produces a streak of light that you can see in the sky. • A meteor is a meteoroid that enters Earth’s atmosphere and burns up. Meteorites • Meteoroids that pass through the atmosphere and hit Earth’s surface are called meteorites. • Classified by composition: stony, iron ,or stony-iron. Video Clip on Meteor Showers • http://www.teachersdomain.org/resources/e ss05/sci/ess/eiu/meteorshower/index.html • Click view What do we do if an NEO is approaching? • Unknown… Still being experimented. • Scientist are calculating ways to use nuclear energy to divert an incoming object. • High energy x-ray pulses produce a shock wave to push the NEO in the opposite direction.