Small Water

A controversial theory that the Earth is being bombarded constantly by comet-like objects the size of small houses and consisting mostly of water has received support from recent satellite observations.

Cosmic Snowball Tracks?

In the image shown below the suspected track of such a cosmic snowball is captured by the visible imaging system of the Polar Satellite as the object vaporized at an altitude of 5,000 to 15,000 miles over the Atlantic Ocean and Western Europe in September, 1996.

Suspected trail of a "cosmic snowball"

Observations indicate that these objects are vaporizing and leaving behind clouds in the atmosphere that are 10-100 kilometers across and have high concentrations of water vapor. This interpretation was first suggested in the mid-1980s from the UV satellite observation of dark spots in the "dayglow" (ultraviolet light produced by sunlight interacting with oxygen in the atmosphere). Large clouds of water vapor would absorb the UV light at the frequencies that the satellite was observing, thus leaving a dark spot or "hole" in the dayglow.

Implications for History of Atmosphere and Oceans

If such a bombardment has continued for long periods, it would have enormous implications for our understanding of the origin and evolution of the Earth's atmosphere and oceans, and perhaps for the evolution of life itself on the planet. For example, the present estimated rate of this bombardment is of order 10 per minute, with each event believed to deposit 20-40 tons (!) of water vapor in the upper atmosphere. This influx would add approximately 1 inch of water to the surface of the Earth every 20,000 years. If an appreciable fraction of this rate has been sustained over the 4.5 billion year history of the planet, such small comets might be responsible for all the water in the oceans and in our atmosphere. Furthermore, there may might be compounds other than water in the bombardment, which could have important implications for various geochemical and biological cycles.

This would imply a rather different scenario than the traditional one that our atmosphere and oceans were formed by gases emitted from the crust of the Earth after its formation. Here is an FAQ (list of frequently asked questions) composed by proponents on this developing and still controversial topic.