The Disintegration of Comets as a Creationist Clock

By Jonathan Ring

Several young-earth creationists have made the claim that comets provide a clue that the solar system, and consequently the Earth and the universe, are young. Since comets disintegrate quickly in the inner solar system, there should be none left if solar system is as old as scientists claim it is. They refute the claim that scientific research has adequately described the existence through the use of the Oort cloud and Kuiper belt comet reservoirs.

Comets are 'floating icebergs' which have been orbiting the sun at great distances since the formation of the solar system according to astronomer Carl Sagan (Druyan and Sagan 1985: 4). Most comets range in size from 1 to 15 kilometers in diameter and consist of ices and other solids (Stern 2003). The only comets visible from Earth, without the use of the most sophisticated technologies, are those that pass close to the sun. In fact, the comet nucleus is not even visible; it is the tail that puts on a show. As a comet gets close to the sun, the ices start to sublimate, causing a cloud of diffuse gas and fine particles known as the coma to be blown away from the sun by solar winds (Druyan and Sagan 1985: 127).

Since comets are so small, they lose a large percentage of their material every time they pass near the sun. Therefore the average lifetime of an individual comet (which has entered the inner solar system) is quite short. For instance, old earth creationist Hugh Ross claims that the lifespan of Halley's Comet is approximately 10,000 years, whereas others comets have given an average lifespan of approximately 2,000 years (Ross 2004: 202). Disintegration is directly related to the orbital period. For instance, a comet with a short orbital period will pass close to the sun more frequently than a longer period comet, and will therefore disintegrate more quickly than the long period one.

Orbits of comets are divided into two categories, long period and short period. Short period comets are further divided into two subcategories based on orbital properties (Nurmi 2002). By observing these orbits and inclinations, astronomers have concluded that a spherical reservoir of comets exists at a great distance from the sun as well as a disc-like reservoir at a closer distance. These reservoirs are thought to be the origin of comets which may eventually enter the inner solar system. The Oort cloud and Kuiper belt are the reservoirs that were proposed to explain the observations of comet orbits. The Oort cloud reportedly consists of approximately 100 trillion comets occupying an immense space at the very edge of the solar system, somewhere between 1,000 and 100,000 A.U. (Druyan and Sagan 1985, Stern 2003). Since an astronomical unit (A.U.) is the distance from the Earth to the sun, these comets are found at distances thousands of times further from the sun than the Earth. Even with the immense number of comets, the volume they occupy is so large that they rarely come into contact with each other. The average distance between them is approximately 20 A.U. (Druyan and Sagan 1985:197). Passing stars and large objects occasionally cause gravitational perturbations which change the orbits of some comets enough to send some into the inner solar system. The result is that the inner solar system receives only a small fraction of the total number of comets in the solar system.

The young-earth creationists have used rapid disintegration rates of inner solar system comets to support a model for a young solar system. The basic claim as used in the argument is summed up by young Earth Creationist and Astronomer Danny Faulkner:

Comets are continually being lost through decay, collisions with planets, and ejections from the solar system. If the solar system were billions of years old, then all comets would have long ago ceased to exist if they were not continually being replaced (Faulkner 2001).

Therefore, young-Earth creationists criticize the reservoir theories that scientists have proposed to explain the existence of comets in the solar system today, namely the Oort cloud and Kuiper belt.

The Oort cloud and Kuiper belt were originally hypothesized as solutions to observations of comet orbits without direct observational evidence. This led Faulkner to claim that, "There are problems with the Oort cloud, the greatest being that there is absolutely no evidence that it even exists!" (Faulkner 2001). Giving credit to Carl Sagan for such an observation, Faulkner misrepresented the famed astronomer's work. The actual quote from Sagan, which Faulkner used as evidence against the Oort cloud, actually reads, ".there is not yet a shred of direct observational evidence for its existence." (Druyan and Sagan 1985: 201).

Scientists have accumulated a large amount of evidence which supports the Oort cloud and Kuiper belt. Originally only theoretical evidence, new technologies have allowed direct observational evidence as well in the last several years. Since young earth creationists attack the time scale accepted by traditional science, it is prudent to look at what evidence actually exists for the existence of the Oort cloud and Kuiper belt.

In 1950, Jan Hendrik Oort first proposed a cloud at a great distance from the sun to explain the observations of comets. Theoretical evidence of the Oort cloud comes from the "random distribution of orbital planes and of perihelia and of the preponderance of nearly-parabolic orbits [of comets]." (Oort 1950). Through the use of computer modeling techniques, astronomers have found that "models of Solar System and Oort cloud formation have repeatedly shown that the formation of an Oort cloud is a natural by-product of the clearing and ejection of debris from the giant planets' region some, 3.5-4.5Gyr ago." (Stern 2003).

However, the Oort cloud failed to explain all of the observed comet traits due to differences in characteristics of long period and short period comets. To explain the short period comets, a disk of comet material lying just beyond the last of the giant gaseous planets was expected. The theoretical evidence eventually led to the idea of the Kuiper belt.

Since technology has increased, observational evidence has been added to the already mounting theoretical evidence. Ground based equipment has been able to confirm the existence of the Kuiper belt in the last 15 years (Stern 2003). The most recent breakthrough in the quest to understand comets and our solar system came recently when an astronomer made the first claim of an actual observation of an Oort cloud object (Irion 2004).

Despite the evidence which supports the Oort cloud and Kuiper belt, some young-Earth creationists such as Faulkner still use comet existence as evidence for a young Earth. This view has not changed even after the observational evidence of the Kuiper belt was collected. As Faulkner states, "At this time it is still quite doubtful that either the Kuiper belt or Oort cloud exist, as they must in an old Solar System." (Faulkner 1997). Just paragraphs before however, he made this observation: ".while the Oort cloud may not be observable, it appears that the Kuiper belt may be.These objects are the only serious threat to the use of the existence of comets as an argument for a young Solar System." (Faulkner 1997)

It seems, then, that this line of evidence for the young-Earth view is misleading. There is little doubt within the scientific community that the Oort cloud and Kuiper belt exist. The young-Earth creationists' attempt to date the age of the solar system, and consequently the Earth, as very young directly opposes accepted scientific evidence. With ever increasing validity through continued research, the proposition of the Oort cloud and Kuiper belt are the best explanation for the existence of comets, despite claims by young-Earth creationists that the existence of comets is evidence for a young earth.

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