That is also a great link. If you can believe curent comet theory and this statement {A Cometary Grand Slam
Comets have been slamming into planets for millennia. As recently as in July 1994, an estimated 21 major fragments of the comet Shoemaker-Levy 9 pummelled the planet Jupiter for six long days. Similarly, the enormous aerial explosion that flattened approximately 500,000 acres (around 202,342 hectares) of pine forest near the Podkamennaya Tunguska River in central Siberia on June 30, 1908, was also perhaps caused by a comet fragment. The energy released by the explosion in the Tunguska event was reckoned at about 10,000,000 to 15,000,000 tons of TNT. By contrast, the atomic bombs that devastated the cities of Hiroshima and Nagasaki during World War II, exploded with a force equivalent to 15,000 and 21,000 tons of TNT, respectively.

However, it looks like the tables may soon be turned. Come July 2005, the first man-made object, built by NASA, will slam into comet Tempel 1, in an effort to study the nature of its nucleus.

NASA's Deep Impact Mission Program
NASA's 279 million-U.S. dollar (197 million-pound) Deep Impact mission program will launch a two-part spacecraft from the Kennedy Space Flight Center, Florida, in January 2004, for a rendezvous with the comet Tempel 1 in July 2005.

Once it reaches the comet, the spacecraft will release a 770-pound (350-kilogram) payload that will blow a crater the size of a football field, seven stories deep, in the sunlit side of the comet. The flyby craft, which will observe the collision from a distance of about 311 miles (500 kilometres) at the closest, will gather important data that will help analyse the structure and composition of the comet's nucleus.

Tempel 1, which was discovered on April 3, 1867, by French astronomer Ernst Wilhelm Leberecht Tempel, is a periodic comet that orbits the Sun once every 5.5 years. NASA scientists decided to conduct their study on this comet as it is estimated to have completed over 100 passages through the inner solar system. Each passage near the Sun is believed to cause changes to the mantle, or the upper crust of the nucleus.

Since comets are thought to be the remnants of the material that formed the solar system some 4.6 billion years ago, the data gathered by the Deep Impact mission program may also shed light on the origin of stars, including the Sun , as well as planets , asteroids , and, of course, comets themselves.

Cometary Facts
There are several theories on the origin of comets. According to one widely accepted view, comets are as old as the solar system and are the remnants of the building blocks that made up Uranus and Neptune . They were tugged out of their nearly circular orbits into extremely elongated ones by the gravitational fields of the outer planets, which were still forming. Hundreds of millions of comet nuclei exist in a region called the Oort Cloud that surrounds the solar system like a bubble. Such nuclei may travel out of the cloud when disturbed by the gravitational force of a nearby star , and enter the inner solar system in an elongated orbit.

About 25 per cent of the nucleus, or core, of a comet is thought to consist of dust and chunks of rocky or metallic material; the remaining 75 per cent is ice. The ice is mainly frozen water with a mixture of compounds containing methane, ammonia, and carbon dioxide radicals, or subunits of molecules. Of the approximately 650 comets that have so far been scientifically recorded, the largest has a nucleus measuring about 42 miles (68 kilometres) in diameter and the smallest about 0.3 mile (0.5 kilometre). Comets smaller than this undoubtedly exist, but they are not bright enough to be detected by light telescopes.

When a comet passes close to the Sun it loses some of its matter, usually about 0.3 per cent of its mass per orbit. The nuclei of comets are slightly less dense than water and are covered by a thin crust of dust. They are extremely fragile and have been observed breaking up into fragments.

As a comet nears the Sun, its ice begins to sublimate -- that is, to pass directly from a solid to a gas form. The gas carries with it some of the loosely bound dust particles. The gas then spreads out around the nucleus, forming a large, thin atmosphere called the coma. Sunlight causes the atoms in the coma to glow, creating a pearly, spherical patch of light up to 62,000 miles (100,000 kilometres) in diameter. If the supply of gases from the nucleus changes, a comet can brighten or fade unexpectedly, which is why astronomers cannot predict how bright a comet will become.

The solar wind, which consists of high-speed atomic nuclei, protons, and electrons, sweeps cometary gases away from the Sun, producing a straight tail up to 93 million miles (150 million kilometres) in length. A second tail consisting of dust particles may also appear. This dust tail is shorter and more curved than the gas tail. A comet tail always points away from the Sun because of the force exerted by the solar wind and the Sun's radiation on the cometary material. Therefore, when a comet travels away from the Sun, its tail or tails are always in front of it. Some comets have been observed to develop as many as nine tails. }

Then somebody has to explain why the tail is immune from obital mechanics. IE the material in the tail is being ejected into a higher orbit, some 93 million miles higher if this page of facts is to be believed. The circumference of the periheilion arc around the sun at 93 million miles further out is much bigger than the arc of the comet itself. For material at the outer end of the arc to cover this larger distance, it has to accelerate perpendicular to the solar wind. Or it has to be traveling outbound from the sun at speeds in excess of light speed by multiple factors. That defies the rules of causality and time as I understand it and thus can not be.

This reinforces the possibility that the ion tail is a light pillar because the luminescence which appears to be at the tail of the comet is actually closer to the observer than the luminescence which appears to be at the head.

Thanks again for that link.

Dan