Credit: Image taken in Stuttgart (Germany); special thanks to Stefan Seip.
A comparison of an image of Comet Tempel 1 taken on July 4, 2005, 0:00
Feb 16, 2006
More than a half-century ago, the distinguished astronomer Fred Whipple offered a scientific theory of comets that came to be known as the “dirty snowball model”. Embraced by virtually all astronomers, the theory explained the “outgassing” of comets as the effect of heating by the Sun. When a comet moves closer to the Sun, ices on the nucleus “sublimate”, or evaporate into space, simultaneously ejecting dusty material held within the ices.
By the 1980s, however, new discoveries began to force changes in the language of comets. The theorized surface water proved far more difficult to find than anyone had imagined. In 1986, visits to Halley’s comet by the European Giotto and Russian Vega probes failed to locate surface water and raised the distinct possibility that the nucleus might not be ejecting water into space. A feature story in the journal Nature following the encounter acknowledged that, “…only indirect and sometimes ambiguous evidence of water has been found; indeed, some facts seem to contradict this hypothesis”.
The flyby of Comet Borrelly by the Deep Space 1 craft in 2001 “detected no frozen water on its surface”, according to a NASA release. "The spectrum suggests that the surface is hot and dry. It is surprising that we saw no traces of water ice," said the lead investigator Dr. Laurence Soderblom.
Then, in January 2004, the Stardust spacecraft passed by Comet Wild 2, identifying a dozen jets of material exploding from the nucleus. The craft plowed through surprisingly dense pockets of dust swirling around the comet, but investigators were astonished that they could not find even a trace of water on the surface, despite the energetic activity.
By the time of “Deep Impact” on July 4, 2005, comet theory had fragmented into mutually contradictory hypotheses—a comet was a dirty snowball, an icy dirtball, a gravel pile, a rubble heap, or an easily-fragmented fluffball.
NASA’s recent report on the Deep Impact mission suggests that investigators found a smattering of water ice on the surface of comet Tempel 1. The problem is that, to account for the water supposedly being “exhaled” by Tempel 1, the investigators needed 200 times more exposed water- ice than they could find.
Advocates of the “electric comet” say that the issue here is not a question of fact so much as one of interpretation. Prior assumptions have hardened into dogma, which has prevented comet researchers from seeing possibilities that might be obvious to those who do not share the dogma. After noting that the surface of Borrelly was “hot and dry”, NASA scientists did not question their theoretical starting point. Soderblom did not doubt the presence of water somewhere. "We know the ice is there," he said. "It's just well-hidden”.
Considering the pattern of new findings, it is time to pose the question that no one has wanted to ask. Why do comet investigators never find the levels of nucleus ices they expect? The absence of detectable water on the nucleus of Wild 2 was particularly mystifying because the pictures revealed cavernous craters with steep cliffs exposing deep subsurface material. The absence of water in such circumstance is no small problem!
The case of missing water is even more severe in the instance of Deep Impact and Comet Tempel 1. If a thin crust of dust hides the water below the surface of the nucleus, one would think that a newly formed crater, estimated to be the size of a football field and perhaps 65 feet deep, would be exactly what was needed to add life to the comet’s water-producing ability. The ice certainly could not be more than a few feet beneath the insulating material—and that’s thinking generously. Any deeper than that, and the Sun’s heating could have nothing to do with the comet’s discharge.
The explosion removed many thousands of tons of material. But prior to impact, the calculated “water” output was 550 pounds per second; and not long after the impact, the calculated output was, once again, 550 pounds per second (See picture above regarding the return to previous level). So despite the impressive explosion, the envisioned sub-surface water refused to reveal itself. By NASA’s own calculations, therefore, Deep Impact has only made matters worse for standard theory.
The electrical theorists suggest that the “problem” is simply one of scientific preconceptions—namely, unfounded assumptions about the “water” content of the coma and its presumed origins.
More than two decades ago, Fred Whipple noted that the inner coma of a comet is a “chemical factory” and that the complex reactions within the coma can leave scientists “confused”. It is not clear “whether the materials we detect come unchanged directly from the nucleus or were manufactured near the surface”, he said.
To solve the dilemma, scientists turned to modeling the possible chemical reactions with the help of supercomputers and spectroscopic observations, beginning with the assumption that volatiles “boil off” the surface via solar heating. From that starting point a theory passed into rigid beliefs and unwarranted statements of “fact”. As the space age has demonstrated so poignantly, the hardened beliefs did not give way even when later visits to comets not only failed to verify the assumptions, but produced a litany of surprises.
No one should be permitted to state as fact the idea that large volumes of “water” fill the comas of comets. The scientific instruments do not see water. What they see as the most abundant companion of cometary dust is the “hydroxyl” radical, OH.
In considering the source of OH, the theorists possess a deficient toolkit. Standard theory has little to work with other than photolysis, the process by which light absorption can break a molecule down into its separate building blocks. But conventional theorists, already “knowing” that the coma is a product of water boiling off the nucleus, concluded with equal confidence that the coma’s water has been broken down by the Sun’s ultraviolet radiation, forming the hydroxyl radical (OH) along with atomic hydrogen and oxygen. By this reasoning, the abundance of OH in a comet nucleus becomes a direct pointer to the abundance of water held by the nucleus.
So the distinction between fact and theory is quickly blurred. A superabundant “leftover” of the hypothesized conversion of water into OH is hydrogen. But in truth, it is not easy to produce hydrogen though any process other than electrolysis. And there is a suspicious absence of adequate experimental work to verify that the photolysis assumed by cometologists is actually feasible on the scale their “explanation” requires.
A much different vantage point on the water question is possible. The unsolved mysteries of the comet will find direct answers in an electrical exchange—the transaction between a negatively charged comet nucleus and the Sun.
In fact there are many avenues for generating OH if you allow for electric discharge and “sputtering” by protons to remove silicates, carbonates, and other rock minerals, together with organic molecules, from the comet’s surface. Electrical sputtering technology is well established in industrial applications, but is far from the minds of astronomers as they consider the mysteries of the comet.
Meanwhile, the surprises continue, and the electric theorists remind us again that surprises are the key to discovery: the findings that have most astonished astronomers are high energy events—extreme ultraviolet light emissions, x-ray emissions, million degree temperatures, supersonic jets, explosive and unpredictable outbursts even beyond the orbits of Jupiter and Saturn, the violent break-up of comets (including the surprising speed at which the parts sometimes separate), and the complete disintegration of comet nuclei millions of miles from the Sun. The very things that comet researchers did not anticipate are the predictable effects of an electric comet.
Of course, if electric sputtering is occurring on a comet’s surface, it is not just another surprise; it is a challenge to all conventional assumptions about water in the comas of comets. Since OH abundance is virtually the only basis for common statements about cometary water, it is essential that the question remain open long enough to allow for consideration of the water issue from another vantage point.
NEXT: Deep Impact—Where’s the Water? (3)
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