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Difference between Asteroid and Comet

December 26, 2008

After watching History Channel’s Mega Disaster “Comet Catastrophe”, there is a question that comes to my mind. What is the difference between a comet and an asteroid?

That’s why I started to browse to answer the question that bothers me most.

What is Asteroid?

  • Asteroids are rocky and metallic objects that orbit the Sun but are too small to be considered planets. They are known as minor planets.
  • Asteroids range in size from Ceres, which has a diameter of about 1000 km, down to the size of pebbles. Sixteen asteroids have a diameter of 240 km or greater. They have been found inside Earth’s orbit to beyond Saturn’s orbit.

Asteroid Belt

Asteroid Belt

  • Most, however, are contained within a main belt that exists between the orbits of Mars and Jupiter.

Some have orbits that cross Earth’s path and some have even hit the Earth in times past. One of the best preserved examples is Barringer Meteor Crater near Winslow, Arizona.

  • Asteroids are material left over from the formation of the solar system. One theory suggests that they are the remains of a planet that was destroyed in a massive collision long ago.
  • More likely, asteroids are material that never coalesced into a planet. In fact, if the estimated total mass of all asteroids was gathered into a single object, the object would be less than 1,500 kilometers (932 miles) across — less than half the diameter of our Moon.
  • Much of our understanding about asteroids comes from examining pieces of space debris that fall to the surface of Earth.
  • Asteroids that are on a collision course with Earth are called meteoroids. When a meteoroid strikes our atmosphere at high velocity, friction causes this chunk of space matter to incinerate in a streak of light known as a meteor. If the meteoroid does not burn up completely, what’s left strikes Earth’s surface and is called a meteorite.

What is Comet?

  • A comet is a small Solar System body that orbits the Sun and, when close enough to the Sun, exhibits a visible coma (atmosphere) or a tail — both primarily from the effects of solar radiation upon the comet’s nucleus. Comet nuclei are themselves loose collections of ice, dust and small rocky particles, measuring a few kilometres or tens of kilometres across.

Comet

Comet

  • Comets have a variety of different orbital periods, ranging from a few years, to hundreds of thousands of years, while some are believed to pass through the inner Solar System only once before being thrown out into interstellar space.
  • Short-period comets are thought to originate in the Kuiper Belt, or associated scattered disc, which lie beyond the orbit of Neptune.
  • Long-period comets are believed to originate at a very much greater distance from the Sun, in a cloud (the Oort cloud) consisting of debris left over from the condensation of the solar nebula.
  • Comets are thrown from these outer reaches of the Solar System inwards towards the Sun by gravitational perturbations from the outer planets (in the case of Kuiper Belt objects) or nearby stars (in the case of Oort Cloud objects), or as a result of collisions.
  • Comets leave a trail of debris behind them. If the comet’s path crosses Earth’s path, then at that point may be meteor showers as the Earth passes through the trail of debris.
  • The Perseid meteor shower occurs every year between August 9 and 13 when the Earth passes through the orbit of the comet Swift-Tuttle.
  • Comets are distinguished from asteroids by the presence of a coma or tail, though very old comets that have lost all their volatile materials may come to resemble asteroids.
  • Asteroids are also believed to have a different origin from comets, having formed in the inner Solar System rather than the outer Solar System.

Recent findings have, however, somewhat blurred the distinction between asteroids and comets.

References:

http://www.solarviews.com/eng/asteroid.htm

http://en.wikipedia.org/wiki/Comet

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