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Name: Jeffrey
Status: other
Age: 50s
Location: N/A
Country: N/A
Date: 1999 - 2000

My 9 year old son has a homework question "Surrounding our solar system is the Oort ____ ____ (two words). I have looked through his reading material, and cannot find an answer, other than the Oort cloud. Please help. Thank You Jeffrey Hero

It is called the Oort Comet Cloud. For short, it is sometimes referred to as just the Oort Cloud.

Comets are a part of our solar system, and not irratic visitors from interstellar space. The distance of this region of where comets seem to originate is about 50,000 AU (AU is an astronomical unit, equal to the average earth-sun distance). This was found by looking at the aphelion (furthest distance from the sun) of many comets. The Dutch astronomer Jan Oort (born in 1900) proposed this in about 1950. By calculating gravitational influence, this 50,000 AU distance is about the limit of our sun's gravitational sphere of influence. It is about 1/3 the distance to the next star. At this distance, a small perturbation of a passing star can easily change the orbit of a comet, and cause it to fall in toward the sun. It is thought that there are about 10^12 comets in this cloud. Since the mass of a comet is about 10^-11 earths, there are only a few earth's mass of comets in the entire comet cloud.

Two theories exist to explain the formation of this cloud. One is that it condensed in place at the time of the formation of our sun. The other is that it formed closer to the sun, but was ejected to 50,000 AU. At this time (2000), we have no direct observation of this cloud. Comets give us many research opportunities in astronomy.

Nathan A. Unterman

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