By Kathy Sawyer
Washington Post Staff Writer
Sunday, June 1 1997; Page A03
The Washington Post
The revelation that house-sized snowballs from outer space appear to be showering Earth with a cosmic rain may sound like an "X-Files" script.
But the evidence is strong enough, and the potential implications significant enough, that astronomers who specialize in tracking near-Earth objects have begun scrambling to try to detect the stealthy snowballs -- which have mysteriously eluded even the most advanced equipment up to now.
And scientists in a number of fields, from planetary geology to atmospheric physics, are scratching their heads as they try to make sense of a phenomenon that represents a dramatic departure from past observations and theories. The riddles it poses are every bit as dramatic as any sci-fi plot.
"I'm honestly, genuinely, deeply puzzled," said Eugene Shoemaker of the U.S. Geological Survey in Arizona, a leading astro-geologist, comet watcher and a co-discoverer of the shattered comet Shoemaker-Levy 9, which plowed into Jupiter in 1994.
"It takes such special characteristics to make these things invisible to all our other observing techniques -- it gives me and most other people I know a bit of a funny feeling. I honestly don't know what to make of it. . . . It's off the wall."
Louis A. Frank of the University of Iowa disclosed his startling discovery Wednesday at a meeting of the American Geophysical Union in Baltimore. He produced a set of images that clearly show water-bearing objects streaking toward the Earth and ballooning into clouds of vapor some 600 to 15,000 miles above the surface.
Frank estimates the loosely packed snowballs -- about 40 feet across, weighing 20 to 40 tons and traveling about 20,000 mph -- strike Earth's atmosphere by the thousands daily and flash into vapor. The resulting clouds punch through to lower altitudes, he says, where the water vapor mixes into the lower atmosphere and falls as rain months later.
Frank had first proposed the existence of unusual small comets that dump vast amounts of water into Earth's atmosphere 11 years ago. If the barrage had continued over the 4.5 billion-year history of the planet, he theorized, the small comets could have delivered enough water to have created the world's oceans. He also suggested they might have transported to Earth the building blocks of life.
Most scientists dismissed Frank's theory, charging that his data was spawned by a flaw in his detector. But he persisted, designing and building a more advanced instrument that was launched aboard NASA's POLAR satellite. It recorded the light trails and water signature of the mystery objects from an orbit 30,000 miles high.
The discovery has revived many questions that made Frank's initial proposal so unpalatable to the scientific community. And it has reignited debate about the nature of the objects and the amounts of water they may have delivered to Earth over geological time. The difference is that now a number of scientists say they believe Frank is seeing something real.
"We've been discussing it for the last 48 hours and we plan to make an attempt" to detect the objects, possibly as early as the next observing run, said Eleanor Helin of the Jet Propulsion Laboratory (JPL) in Pasadena, Calif. Helin is the lead scientist for the joint NASA/Air Force NEAT (Near Earth Asteroid Tracking System) program, which has a telescope facility on the Hawaiian island of Maui.
Helin said the team might invite Frank to join the effort, and advise about how and what to look for. She said many on the team doubt that normal observing techniques can pick up such small, fast-moving objects, which Frank believes are coated in black carbon until they break up in the atmosphere.
In 1988, JPL space scientist Clayne Yeates used the Spacewatch Telescope at Kitt Peak in Arizona to test Frank's hypothesis and learned just how difficult the observing challenge was. Using Frank's data on the objects' number, speed and direction of motion, Yeates decided to operate the telescope in an unusual fashion, leading his targets as if he were aiming a rifle at a skeet shoot. This way, Yeates thought, he could hold the objects in view long enough to record their passing.
Yeates, who is now deceased, "nearly went blind" trying to analyze the resulting images, Frank recalled later. After eliminating all the known objects (stars, satellites, cosmic rays, etc.) and false signals in 171 images, he said, there were a few short, faint streaks from unidentified objects. Yeates and Frank considered the streaks a confirmation of the microcomets' existence, but the wider scientific community rejected the results as borderline -- possibly representing background "noise."
Frank last week urged both NEAT and Spacewatch tracking experts to revisit Yeates' "cosmic skeet shoot" technique.
Other experts recommended additional methods for testing Frank's evidence, such as attempting to use satellite-borne lasers to measure the incoming water. "There is an immediate need to verify this . . . to sense the composition of the water," said geochemist Gustaf Arrhenius of the Scripps Institution of Oceanography in California.
If Frank's interpretation of the evidence is true, he said, it "would essentially change our ideas about the dynamics of growth and shrinkage of the oceans, and also about the composition of the atmosphere."
Brian Marsden of the Harvard-Smithsonian Center for Astrophysics, who operates an official clearinghouse for astronomical observations, acknowledged that current surveys of near-Earth objects cover only about 1 percent of the sky. But he estimated that even in that small sample observers should pick up several small comets per night -- if Frank's estimates are correct.
"The numbers just don't jibe," Marsden said, echoing the concern of many. There are perhaps a million times too many of these small objects in Frank's model, he said, when compared to other evidence. "We should be seeing these quite easily in some of the surveys," he said. "We see smaller things from time to time out as far as the moon."
Shoemaker, who said he hopes to mobilize the Lowell Observatory in Flagstaff, Ariz., to look for the objects within the year, said Frank's estimate "represents a huge spike in the distribution" of comets. That is, there should be a smooth continuum from a few large ones to many smaller ones, based on various observations including the record of cratering on the moon. "There's a good record right down to centimeter size and there's no significant bump in the distribution in the last 100 million years" of the sort Frank's observations indicate, he said.
If Frank is correct, Shoemaker said, then the most plausible explanation for the objects is a sudden storm of icy fragments from a shattered comet traveling along roughly the same path around the sun as Earth. This most likely would have happened within the last 100,000 years or so, he said, and might last for 10,000 years or less. "I would be forced to that conclusion, if these objects are real. We're in a Lou Frank miniature comet storm."
But that still leaves the quandary that most troubles scientists when they consider Frank's hypothesis. "We don't see these hitting the moon," Shoemaker said. If they're hitting Earth, by all accounts, there is no way they could avoid the moon.
Frank has argued that a soft, powder puff of a snowball might escape detection by seismic instruments on the moon. But Shoemaker and others assert that, at those velocities, the snowballs should deliver half the impact shock of a rocky object and certainly should show up in seismic signals. Besides that, Shoemaker said, they should "blow holes" in the loose, yards-thick layer of dust and rock that blankets the lunar surface.
The missing lunar impacts, like dogs that fail to bark in the night, represent "the most significant single difficulty, one that it's just hard to get around," he said. "On the other hand, these observations are extraordinary . . . I'm casting around in desperation."
SPOTTING WATER
Evidence for the cosmic snowballs was gathered by NASA's POLAR satellite, which is orbiting 30,000 miles above Earth equipped with an instrument called the Visible Imaging System (VIS). VIS, which was specially designed by Louis A. Frank of the University of Iowa, uses a filter that detects visible light emitted only by fragments of water molecules.
@CAPTION: (This graphic was not available)
SOURCE: NASA Facts, December 1995
@CAPTION: The Visible Imaging System on the POLAR
satellite took this image of an atmospheric hole, a small dark
area against the Earth's dayglow, April 6, 1996.
� Copyright 1997 The Washington Post Company
-------------------------------------------------------------------------------------------------
JUNE 9, 1997 VOL. 149 NO. 23
SCIENCE
THE GENTLE COSMIC RAIN
DON'T WORRY IF YOU MISSED HALE-BOPP; AS MANY AS 43,000
SMALLER COMETS COULD REACH EARTH TODAY
BY JEFFREY KLUGER
Hardly anybody took Louis Frank seriously when he first proposed, more than 10 years ago, that the Earth was being bombarded by cosmic snowballs at the rate of as many as 30 a minute. Part of the problem was how preposterous his theory sounded: every day, he suggested, tens of thousands of icy comets, each the size of a small house and containing 40 tons of water, were vaporizing in the upper atmosphere and raining down on Earth. It didn't help that the University of Iowa physicist happened to release his findings on April 1, 1986. "Newspapers," he recalls, "phoned to ask if this was an April Fool's joke."
Frank is unlikely to hear that kind of question again. Last week, at the American Geophysical Union's annual convention in Baltimore, Md., he backed up his theory with fresh evidence: satellite images that capture his cosmic hail in midflight. Suddenly it seems entirely possible that the source of much of the water on Earth--and even of life itself--might be Frank's "gentle cosmic rain."
Frank first began formulating his theories in the 1980s when he was analyzing satellite pictures and found the atmosphere in the images flyspecked with thousands of spots. The altitude of the flecks and the wavelength of light they absorbed led him to conclude that they were clouds of extraterrestrial water that had somehow been carried to Earth.
Few others were convinced, however, because of the graininess of the images. So Frank came to the Geophysical Union meeting last week armed with better photos from a new satellite, and this time his pictures carried the day. "We have a large population of objects that have not been detected before," he now says confidently. Extrapolating from the number of those objects he saw in his pictures, he estimated that as many as 43,000 of these celestial snowballs arrive on Earth every day.
How could so many comets stay hidden so long? For one thing, they are not true comets. Big-name comets like Hale-Bopp may measure 20 miles across--giants compared with Frank's 40-ft. pellets. The large comets are studded with rock and metal, while Frank's are almost all water.
It's a good thing for us that so much of what rains down on Earth amounts to cosmic bird shot. A collision with a full-scale comet would be a global calamity; the minicomets, by contrast, are remarkably fragile. Well before they hit the planet--between 600 miles and 15,000 miles up--they begin to disintegrate. Sunlight then breaks them down further, transforming them into ordinary clouds that produce ordinary rain. Over the course of 20,000 years, this cosmic sprinkling can add an inch of water to the planet; multiplied by the Earth's 4.5 billion-year history, that could help account for the oceans themselves.
But it is not just water the comets import. In order to remain intact in space, they must be held together by a supporting shell. Frank believes that shell is made of carbon, created as cosmic rays break down traces of methane. Carbon, of course, is a basic building block of biology. It may be, Frank says, that his comets carried the very stuff of life to Earth, helping give rise to all the planet's creatures. That may still sound preposterous, but this time nobody's saying April Fool.