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Information about comets
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Published on January 10, 2008

Author: Marietta1

Source: authorstream.com

Meteorites, Asteroids, and Comets:  Meteorites, Asteroids, and Comets Chapter 25: 0 Meteorites:  Meteorites Distinguish between: Meteoroid = small body in space Meteor = meteoroid colliding with Earth and producing a visible light trace in the sky Meteorite = meteor that survives the plunge through the atmosphere to strike the ground 0 Slide3:  Which one of those objects would appear as a “shooting star”? Only meteoroids. Only meteors. Only meteorites. Meteors and meteoroids. Meteors and meteorites. Meteoroids and meteorites. All three. Meteorites:  Meteorites About 2 meteorites large enough to produce visible impacts strike the Earth every day. Statistically, one meteorite is expected to strike a building somewhere on Earth every 16 months. Typically impact onto the atmosphere with 10 – 30 km/s (≈ 30 times faster than a rifle bullet). Sizes from microscopic dust to a few centimeters. 0 Meteor Showers:  Meteor Showers Most meteors appear in showers, peaking periodically at specific dates of the year. 0 Meteoroid Orbits:  Meteoroid Orbits Meteoroids contributing to a meteor shower are debris particles, orbiting in the path of a comet. Spread out all along the orbit of the comet. Comet may still exist or have been destroyed. Only few sporadic meteors are not associated with comet orbits. 0 Slide7:  What kind of pattern would you expect to see, comparing the tracks of various meteors of one shower? The tracks should have random directions. The tracks should all be parallel. The tracks should all appear to come from the same point in space. The tracks should all appear to move toward the same point in space. Radiants of Meteor Showers:  Radiants of Meteor Showers Tracing the tracks of meteors in a shower backwards, they appear to come from a common origin, the radiant. ↔ Common direction of motion through space. The Perseid Meteor Shower 0 Slide9:  The Leonid Meteor Shower in 2002 0 Slide10:  Would you expect a meteor shower to be equally intense each year? Yes, because all the meteors should orbit the sun in about 1 year, so there should be no fluctuations from year to year. Yes, because the meteors are evenly distributed over the entire former comet orbit. No, because the meteors should be concentrated around the former location of the comet, which orbited around the sun with a longer period than 1 year. No. In fact, they should only be visible in one year at all. Meteorite Impacts on Earth:  Meteorite Impacts on Earth Over 150 impact craters found on Earth. Famous example: Barringer Crater near Flagstaff, AZ: Formed ~ 50,000 years ago by a meteorite of ~ 80 – 100 m diameter 0 The Origins of Meteorites:  The Origins of Meteorites Planetesimals cool and differentiate; Collisions eject material from different depths with different compositions and temperatures. Meteorites can not have been broken up from planetesimals very long ago → Remains of planetesimals should still exist. → Asteroids 0 Asteroids:  Asteroids Last remains of planetesimals that built the planets 4.6 billion years ago! 0 Slide14:  Where do we find most asteroids in the solar system? In a belt between the Earth and Mars. In a belt between Mars and Jupiter. In a belt far outside the orbits of the planets. On highly elliptical orbits, coming as close to the sun as Mercury’s orbit, and reaching as far out as Pluto’s orbit or beyond. In elliptical orbits around Jupiter. The Asteroid Belt:  The Asteroid Belt Pluto Neptune Uranus Saturn Jupiter Mars (Distances and times reproduced to scale) 0 Most asteroids orbit the sun in a wide zone between the orbits of Mars and Jupiter. The Asteroid Belt:  The Asteroid Belt Sizes and shapes of the largest asteroids, compared to the moon Small, irregular objects, mostly in the apparent gap between the orbits of Mars and Jupiter. Thousands of asteroids with accurately determined orbits are known today. 0 Slide17:  What causes the divisions (e.g., Cassini Division) in the rings of Saturn? Orbital resonances with moons orbiting Saturn outside the ring system. Material close to an orbit of a moon inside the ring system being swept up by the moon. Random fluctuations causing some regions around Saturn to be empty. Orbital resonances with moons orbiting Saturn inside the ring system. Kirkwood Gaps:  Kirkwood Gaps The asteroid orbits are not evenly distributed throughout the asteroid belt between Mars and Jupiter. There are several gaps where no asteroids are found: Kirkwood gaps These correspond to resonances of the orbits with the orbit of Jupiter. Example: 2:3 resonance 0 Non-Belt Asteroids:  Non-Belt Asteroids Apollo-Amor Objects: Not all asteroids orbit within the asteroid belt. Asteroids with elliptical orbits, reaching into the inner solar system. Some potentially colliding with Mars or Earth. Trojans: Sharing stable orbits along the orbit of Jupiter. 0 Comets:  Comets Comet Ikeya-Seki in the dawn sky in 1965 0 Slide21:  Throughout history, comets have been considered as portants of doom, even until very recently: Appearances of comet Kohoutek (1973), Halley (1986), and Hale-Bopp (1997) caused great concern among superstitious. Comet Hyakutake in 1996 0 Slide22:  Where on its orbit does a comet spend most of its time? 1 2 4 3 Two Types of Tails:  Two Types of Tails Ion tail: Ionized gas pushed away from the comet by the solar wind. Pointing straight away from the sun. Dust tail: Dust set free from vaporizing ice in the comet; carried away from the comet by the sun’s radiation pressure. Lagging behind the comet along its trajectory 0 Slide24:  Where is the sun with respect to this comet? 2) 3) 4) 5) 1) Gas and Dust Tails of Comet Mrkos in 1957:  Gas and Dust Tails of Comet Mrkos in 1957 0 Comet Hale-Bopp in 1997:  Comet Hale-Bopp in 1997 0 Fragmentation of Comet Nuclei:  Fragmentation of Comet Nuclei Comet nuclei are very fragile and are easily fragmented. Comet Shoemaker-Levy was disrupted by tidal forces of Jupiter Two chains of impact craters on Earth’s moon and on Jupiter’s moon Callisto may have been caused by fragments of a comet. Animation 1 Animation 2 0 Fragmenting Comets:  Fragmenting Comets Comet Linear apparently completely vaporized during its sun passage in 2000. Only small rocky fragments remained. 0 Slide29:  The fragments of a comet can produce a new … Moon of Jupiter. Moon of Mars. Planet. Meteor shower. Group of asteroids. The Geology of Comet Nuclei:  The Geology of Comet Nuclei Comet nuclei contain ices of water, carbon dioxide, methane, ammonia, etc. (Materials that should have condensed from the outer solar nebula). Not solid ice balls, but fluffy material with significant amounts of empty space. 0 “Dirty snowballs” The Deep Impact Mission:  The Deep Impact Mission Video 1 Video 2 Placing a probe into the path of Comet Tempel 1 and documenting the result of the impact Impact: July 4, 2005 0 The Origin of Comets:  The Origin of Comets Comets are believed to originate in the Oort cloud: Spherical cloud of several trillion icy bodies, ~ 10,000 – 100,000 AU from the sun. 10,000 – 100,000 AU Oort Cloud Gravitational influence of occasional passing stars may perturb some orbits and draw them towards the inner solar system. Interactions with planets may perturb orbits further, capturing comets in short-period orbits. 0 The Kuiper Belt:  The Kuiper Belt Second source of small, icy bodies in the outer solar system: Kuiper Belt, at ~ 30 – 100 AU from the sun. Pluto and Charon may be captured Kuiper-Belt objects. 0 Beyond the Solar System:  Beyond the Solar System 0

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