This image may show an oxygen trail created when a small comet was disrupted as it approached our planet on September 15, 1996. This image was taken by the Polar spacecraft's Earth Camera in ultraviolet wavelengths. The oxygen trail has been superposed upon a "Face of the Earth" map of our planet. Click on image for full size (26K GIF) Courtesy of Dr. Louis A. Frank, The University of Iowa and NASA

These snowballs may really be small comets. If the hypothesis is correct, these snowballs are millions of times smaller than comets like Halley's or Linear, but they are mainly made of water like these larger comets. They lack dust and iron though and so they do not glow or produce a bright tail.

These small comets may have been crashing into the Earth for the last 4.5 billion years! If that's true, then some or all of the Earth's water probably did come from these small comets. It's been estimated that one small comet hits the Earth every three seconds. But, don't worry about getting hit by one of these snowballs! Small comets are not a danger to humans on Earth. They get torn apart at about 800 miles above the Earth and are vaporized by the Sun by about 600 miles above the Earth.

This may sound like something out of a cartoon show, but the Polar spacecraft may have confirmed the existence of these small comets originally found by Louis A. Frank of the University of Iowa. The Polar spacecraft sees the small comets from really far away. So, the next step is to send a spacecraft to see the small comets up close! That will help us to know whether or not this snowball hypothesis is correct!

Some scientists do not believe that Dr. Frank is actually seeing small comets. They do not believe the small comets hypothesis is correct. They think there is evidence that whatever Dr. Frank has discovered, it cannot be comets. Scientists are still debating whether the small comets hypothesis is true or not.