[An excerpt:  Comets by Dr. Jason Lisle]

Comets are balls of ice and dirt which orbit the sun, often in highly eccentric orbits. The solid central portion of a comet is called the nucleus. Comets generally have a region of vaporized material surrounding them which appears as a faint “fog”—this is called the “coma.” Comets spend most of their time moving slowly near the point in their orbit that is farthest from the sun (aphelion). As they approach the sun, they speed up and slingshot around the sun, moving fastest at the closest point (perihelion). It is during these points of close approach that many comets develop a “tail”—a stream of vaporized material which extends away from the comet. The tail points away from the sun, because the material is swept away by solar wind and radiation. Often two tails develop: an ion tail consisting of light charged particles, and a dust tail containing heavier materials. The ion tail is slightly blue in color; it is straight and points directly away from the sun. The dust tail is white and is generally curved. Sometimes only one of the two tails is visible.

A comet’s tail (or tails) is an indication that comets cannot last forever. The tail means that the comet is losing material; a comet gets smaller every time it orbits the sun. It has been estimated that a typical comet can only orbit the sun for about 100,000 years at most before completely running out of material. (This is an average figure, of course; the exact life span would depend on how big the comet is to begin with, and the parameters of its orbit.) Since we still have a lot of comets, this suggests that the solar system is much younger than 100,000 years.  This agrees perfectly with the Bible. Clearly, 4.5 billion years would be an absurdly inflated age for comets.

How do secular astronomers attempt to reconcile this with their belief in billions of years? Since comets can’t last that long, secular astronomers must assume that new comets are introduced to the solar system to replace those that are gone, so they’ve invented the idea of an “Oort cloud.” This is supposed to be a vast reservoir of icy masses orbiting far away from the sun. The idea is that occasionally an icy mass falls into the inner solar system to become a “new” comet. It is interesting that there is currently no evidence of an Oort cloud, and there is no reason to believe in one if we accept the creation account in Genesis. Comets are consistent with the fact that the solar system is young.

Source: http://www.answersingenesis.org/articles/tba/age-of-the-universe-2

Footnotes

14.Named after Dutch astronomer Jan Oort. Back

Does Lisle make a good argument that the universe must be younger than 100,000 years based on what astronomers know about comets (dirty snowballs)?  Is the "Oort cloud" more human imagination or science?  Which explanation are you more likely to believe?  (Pics).http://vananne.com/serpentdove/Comets.htm

Comets