28-06-2008 Vagabonds of our Solar System (Article143)

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Simon Kenny
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28-06-2008 Vagabonds of our Solar System (Article143)

Post by Simon Kenny » Wed Dec 31, 2008 10:32 am

Vagabonds of our Solar System (Article143)

The dictionary describes a vagabond as: ‘an idle wanderer, tramp, vagrant, nomad, a rascal or a rogue…’ This description perfectly describes the Comets, Asteroids and Meteoroids that inhabit the outer reaches of our Solar System, some of which pass us by once in a while.

The orbits of the planets and their moons are pretty well known and understood and basically they all follow the same plane called the ecliptic which has the Sun at its center. But our ‘vagabonds’ do not always follow this pattern and while the cycles of some of the Comets are known and predictable, if one has a cycle of thousands of years we would not even know about it yet.

Asteroids, Meteoroids and Comets are relics of the ‘leftovers’ after our Solar System formed billions of years ago. If fossils are important to palaeontologists, then our ‘vagabonds’ are of equal importance to astronomers. So, what’s the difference between them? Comets are composed of ice and dust and are often described as ‘dirty snowballs’, whereas Asteroids are rocky bits of the solar nebula that never quite made it as a full sized planet. A Meteoroid is a chunk of rock in space and is just a smaller version of an Asteroid. There is no official dividing line between them but the term Asteroid is generally applied to rock chunks bigger than a few hundred metres across.

All of these objects can break into fragments and if any of these bits survive the fall to Earth they are known as Meteorites and amazingly about 300 tons of extraterrestrial matter falls to earth each day. Meteorites are quite rare and it is no surprise that they are highly valued both by scientists and collectors. Depending on their composition meteorites are classified as irons, stones, or stony irons.
A meteor is that brief flash of light that we see at night when a meteoroid enters the Earth’s atmosphere and is more commonly called a shooting star. On very rare occasions a whole Asteroid can hit Earth and one such 10 mile wide Asteroid is thought to have wiped out the dinosaurs about 65 million years ago. So, while they are only bit players in our Solar System they can cause significant consequences for our planet.

So, where in our Solar System do the asteroids exist? For very good reasons astronomers figured that there should be a planet in the great space between Mars and Jupiter on the ecliptic. In the late 1700’s six German astronomers organised an international group to search for this missing planet. They jokingly called themselves the ‘Celestial Police’. But, before they even got started a Sicilian astronomer called Giuseppe Piazzi discovered an asteroid called Ceres (after the patron goddess of Sicily in Roman mythology) and it was exactly where the ‘missing planet’ was expected. At 900 Kms. diameter it is small and is known as a minor planet, or asteroid.

Since 1800hundreds of asteroids have been discovered and today, dozens of asteroids are discovered each month, many by amateurs. Did the ‘missing planet’ ever exist and did it explode or get torn apart and produce this population of asteroids orbiting between Mars and Jupiter? This idea has been discarded simply because the combined mass of all the asteroids, plus an estimate of those yet to be discovered, would result in an object only 1,500 Kms. in diameter. This is too small to be considered a missing planet and it looks like the asteroids are ‘leftovers’ from the time of the formation of the Solar System.

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