Chapter 2 - Commets and Meteor
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- Created on: 14-04-13 09:14
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- Astronomy - Chapter 2 - Planetary System - Comets and Meteors
- Comet orbits
- The orbit of a comet is elliptical, with a high eccentricity (a planet has a near circular orbit by comparison, with a low eccentricity)
- Kuiper Belt and Oort Cloud
- Short-period comets have comets periods less than 200 years and originate from the KUIPER BELT
- The Kuiper Belt is a thick disc-shaped region of icy bodies that lies beyond Neptune (between 30 - 50 AU)
- A famous short-period comet is Comet Halley with a period of 76 years
- Long-period comets originate from the Oort Cloud
- The Oort Cloud is a spherical distributionof cometary nuclei at the outer reaches of the Solar System (50,000 AU from the Sun)
- Even though there is no evidence for the Oort cloud there is strong support for its existence
- Their paths around the Sun are in either sense (clockwise or anticlockwise)
- Orbits are often highly inclined to the ecliptic
- A high percentage of them originate at vast distances (typically 50,000 AU) from the Sun
- A famous comet is the Comet Hale-Bopp in 1997
- Short-period comets have comets periods less than 200 years and originate from the KUIPER BELT
- Comet facts
- Comet tails
- As a comet approaches the sun, the temperature rises and gas and dust form an extremely rarefied spherical COMA that surrounds the nucleus up to 100,000 km across
- A comet can develop two (or more) tails:
- A blue coloured, straight ION tail consisting of atoms and molecules of gas (carbon monoxide) that have been ionised by the solar wind and when they de-excite atoms emit light by fuorescence
- A lighter coloured shorter boader and slightly curved DUST tail produced by radiation pressure that pushes particles out of the nucleus; this tail of dust and git shines by reflecting sunlight and its curvature is due to the individual dust particles
- Comet tails can be several millions of kilometres long
- The comet tail enlarges as it approaches the Sun
- Comets are balls of rock and ice (often called 'dirty snowballs' or icy dirtballs')
- The nucleus is rock and ice and dust
- Comet tails
- Origin of Meteoroids, Meteorites and Micrometeorites
- Meteoroids are pieces of dust or rock that orbit the Sun with many entering the Earth’s atmosphere
- The origin varies - some are broken fragments of colliding asteroids whereas others are formed through impacts with the surface of Moon or Mars
- Many are so small MICROMETEORITES, weighing just a few milligrams. They dont burn but sink into Earth
- If a meteoroid survives its passage into Earth and lands its called a METEORITE; there are 3 major categories
- stones
- Iron
- Stony-irons
- Meteoroids are pieces of dust or rock that orbit the Sun with many entering the Earth’s atmosphere
- PHOs - Potentially Hazardous Objects
- Near-Earth Objects (NEOs) might come closer to Earth than 0.3AU (45 million km)
- NEOs have projected orbits that might bring them even closer to our planet
- These POTENTIALLY HAZARDOUS OBJECTS(PHOs) have orbits that bring them closer to us than 0.05AU (7.5 million km)
- Like the richture scale for earthquakes the TORINO SCALE goes from 0-10 on the likelihood of an collision and the estimated kinetic energy
- From 0-1 indicate likely misses or collisions
- However 8,9 and 10 show a certain collision capable of inflicting world-wide devastation
- Such as global change, natural disasters but extreme that could threaten the future civilisatio
- Impacts with the Solar System
- Research of craters/impacts on the surface of Earth
- Direct viewing of impacts using telescopes
- Simulating impacts – as with the Deep Impact mission to study the effect of an impactor on the formation of craters and the structure of a comet
- Seisomology experiments left in the ALSEPs package on the Moon
- Study of lunar rocks brought back to Earth by the Apollo astronauts
- Research and the use of computer simulations using data and images gained by space missions
- Meteor showers
- At certain times in the year there is a massive increase in the number of meteors
- This occurs when when the Earth passes through a meteor stream left in the wake of a comet
- The increased number of dust particles entering and burning up in the atmosphere causes a meteor shower
- Meteors
- When they enter our atmosphere, friction causes the meteoroid and surrounding air to heat up producing a short streak of incandescentlight - a METEOR or shooting star
- Meteors with a magnitude of -3 or brighter are called FIREBALLS
- Comet orbits
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