After, long thought the font of life on Earth, may not come from Earth at all.
That's the startling theory propounded by scientist Louis Frank. Dr. Frank says there is now evidence to show that while comet Hale-Bopp decorated the sky this spring, thousand of its tiny cousins may have been quietly showering water on Earth. Frank contends the steady patter of this cosmic rain, over the eons, may be responsible for filling the planet's oceans.
Some scientists laughed when Frank suggested the idea 11 years ago. Now the space physicist from the University of Iowa in Iowa City has what he believes is at least partial proof that microcomets may be a primary source of our oceans and may have spiked the early seas with organic material that nurtured the rise of earthly life. If true, the findings could fundamentally reshape scientific thought about the beginnings of life on Earth.
Yesterday, at a meeting of the American Geophysical Union here, he showed pictures of what appear to be water-bearing objects, the size of a small house, hitting the outer atmosphere. National Aeronautics and Space Administration instruments took the images from a Polar satellite - the first space-based observatory equipped to pick up the objects' ultraviolet and visible light trails, including the distinctive visible light "signature" of water.
"We detect these objects at a rate that suggests Earth is being bombarded by thousands [of them] per day," Frank says. He estimates they would add an inch of water to the global ocean every ten thousand years. That's enough to fill the ocean over geological time. Frank noted that there may be enough water in microcomets inside the orbit of Jupiter to constitute a volume of water equal to our ocean.
These microcomets are fluffy snowballs consisting mostly of water ice plus a mix of other materials, including organic chemicals. In Frank's scenario, small 20-to-40-ton "snowballs" break up 600 to 15,000 miles out from Earth. Their water clouds spread out in patches, mix into the atmosphere, and eventually reach the surface. In satellite images, they appear as dark holes 15 to 25 miles across.
Frank first formed his hypothesis when he saw such holes in 1986 images that couldn't detect water the way the Polar satellite images now can. Robert Meyer of the Naval Research Laboratory in Washington says he used to be a skeptic about Frank's theory. Now, he says "I'm convinced the phenomena are real." He adds that the emissions from the microcomets "are the smoking gun for the water."
The new images alone do not definitively prove the case about microcomets as a source of Earth's water. As George Withbroe, science director for NASA's Sun-Earth connection program, notes: "We need to look closely at measurements from other sensors to find out if they see related signatures in the atmosphere, now that we have learned more about what to look for."
This is especially true concerning Frank's speculation that microcomets may bring significant amounts of organic chemicals. "This relatively gentle 'cosmic rain' - which possibly contains simple organic compounds - may well have nurtured the development of life on our planet," he says.
He adds that instruments on the space shuttle could look for such materials as the incoming microcomet cloud passes harmlessly by the spacecraft.