Comets
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[edit] Claim
One claim of the Young Earth Creationists is that the age of short-period comets can be used to find the age of the Earth.
[edit] Examples
- "Each time a comet orbits the sun a prodigious amount of mass is lost. Comets are small, averaging perhaps a kilometer in diameter.
- They cannot sustain many orbits before they disintegrate and disappear. Short period comets last for about 10,000 years. Multitudes of short-period comets in the heavens are witnesses that the solar system is young." (Evolution 101, J F Griggs)
- "Russian astronomer Professor S. K. Vsekhsviatsky, Director of the Kiev Observatory, has studied periodic comets extensively and written two standard works on the subject. He has come to the conclusion that they are losing their luminosity and the matter which constitutes them at such rapid rate that a comet will disintegrate completely within 50 to 60 revolutions of the solar system. Halley's comet could thus be less than 6,000 years old." [1]
[edit] Discussion
This argument works (or, rather, fails to work) by combining a grain of scientfic truth with a ton of false assumptions.
First, the fact: according to astronomers, a comet can indeed only go so many times around the Sun before it disintegrates. This is quite true.
But can we use this fact to put a date on the Earth? Well, let's give it a try. The comet with the shortest period is Encke's comet, with a period of only 3.3 years[2]. Putting this together with the claim that "a comet will disintegrate completely within 50 to 60 revolutions of the solar system", we find that, using the Creationist method, the Universe is no more that two hundred years old. Even if we were generous, and let the comet go, not fifty, but five hundred times around the sun before disintegrating, that still puts the creation about three hundred years after the birth of Christ.
Obviously, something has gone horribly wrong with the Young Earth argument. They don't want the Earth to be that young! What's gone wrong, as any astronomer could tell you, is the assumption that Encke's comet, and all the other short period comets, have always been short period comets. Unless the Universe is in fact mere centuries old, this assumption cannot be true: and it isn't. There are, in fact, new short orbit comets turning up all the time.
- "Because of their high mortality rates, periodic comets cannot have been periodic for long but must originally have been comets of very long periods having nearly parabolic orbits. Within the recent past (perhaps the last few thousand years) their orbits have been drastically altered to their present relatively small size by perturbations produced by the planets, especially Jupiter. Those occasional comets that are highly spectacular, and hence cannot have suffered appreciable disintegration, almost invariably have nearly parabolic orbits, and also they have not been seen before in recorded history." George Abell, Exploring the Universe (Dallas: Holt Rinehart and Winston, 1969) p. 339-340
So since there are new short period comets arriving constantly, it is futile to proclaim that they must have been in those orbits for ever. It makes no more sense to say "Short period comets last for about 10,000 years. Multitudes of short-period comets in the heavens are witnesses that the solar system is young"; than it would make sense to say: "Mice live to about three or four years, maximum. Multitudes of mice are proof that the Earth is no more than four years old".
