Facts about Asteriods

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Subject: Facts about Asteriods Mon Jun 05 2006, 12:48

I'M BACK!! Yes that's right Lily is back in action and she's going to be posting essay after essay. Question is how many can she do now??!? We'll just have to see where it goes - sit back - relax and enjoy the ride of knowledge through Lily's insanity haha!

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On the first day of January 1801, Giuseppe Piazzi discovered an object which he first thought was a new comet. But after its orbit was better determined it was clear that it was not a comet but more like a small planet. Piazzi named it Ceres, after the Sicilian goddess of grain. Three other small bodies were discovered in the next few years (Pallas, Vesta, and Juno). By the end of the 19th century there were several hundred.

Several hundred thousand asteroids have been discovered and given provisional designations so far. Thousands more are discovered each year. There are undoubtedly hundreds of thousands more that are too small to be seen from the Earth. There are 26 known asteroids larger than 200 km in diameter. Our census of the largest ones is now fairly complete: we probably know 99% of the asteroids larger than 100 km in diameter. Of those in the 10 to 100 km range we have cataloged about half. But we know very few of the smaller ones; there are probably considerably more than a million asteroids in the 1 km range. The total mass of all the asteroids is less than that of the Moon.

Asteroids, or minor planets, are small, rocky (or sometimes metallic) bodies with no atmospheres. There are hundreds of thousands of minor planets; nearly 100,000 have been numbered, and more than 12,000 have been named.

Only a few minor planets have been visited by spacecraft: Gaspra, Ida and its satellite Dactyl, Mathilde, and Eros. Therefore, most of our understanding of minor planets comes from Earth-based optical and radio telescope observations. Minor planets are divided into classes based upon the sizes and shapes of their orbits and also upon their spectral characteristics (essentially, their brightness and color). In addition, a few meteorites found on Earth have been identified as pieces of specific minor planets.

Minor planets are classified into broad categories such as C-type, S-type, or M-type according to their brightness and color (technically, their spectra). Brightness, or albedo, is a measurement of how well the object reflects light. Albedo ranges from 0 (perfectly black) to 1 (perfectly reflecting). Most minor planets are relatively dark objects with albedos ranging from a carbon-black 0.03 to a dark 0.22. The composition of asteroids can be determined by breaking down the light they reflect into a spectrum, a graph of how reflective the object is at each wavelength of light. Astronomers can often identify the abundances of silicate minerals in spectra. Based on those identifications, different classes of meteorites found on Earth have been linked to the different classes of asteroids.

Carbonaceous or C-type Asteroids are more than 75 percent of asteroids fall into this category. With albedos of 0.03 to 0.09, these objects are very dark. Their compositions are similar to carbonaceous chondrite meteorites. These asteroids have approximately the same chemical composition as the Sun, but lack hydrogen, helium, and other volatiles. C-type asteroids are most commonly found in the outer regions of the main asteroid belt.

Silicaceous or S-type Asteroids are approximately 17 percent of known asteroids are S-type. They have fairly bright albedos ranging from 0.10 to 0.22. Moving in orbits within the inner regions of the main asteroid belt, S-type asteroids are likely equivalent to the ordinary chondrite meteorites, composed of rocky materials plus a small amount of metallic iron.

Metallic or M-type Asteroids these are the mid-region main belt objects are relatively bright, with albedos ranging from 0.10 to 0.18. M-type asteroids are composed of metallic iron, like the iron meteorites.

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Essay number 1 out of - I don't know haha. We'll just have to say but that makes 19 essays in 2 weeks haha.

Sources for this wonderful essay - besides my knowledge and books can be found on this site for your enjoyment: http://space.about.com/od/asteroids/

Subject: Re: Facts about Asteriods Tue Jun 06 2006, 10:22

Insanity doesn't begin to describe you my dear - 50 points.

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