Cosmos - Carl Sagan [45]
Modern planetary scientists sometimes argue that the collision of a comet with a planet might make a significant contribution to the planetary atmosphere. For example, all the water in the atmosphere of Mars today could be accounted for by a recent impact of a small comet. Newton noted that the matter in the tails of comets is dissipated in interplanetary space, lost to the comet and little by little attracted gravitationally to nearby planets. He believed that the water on the Earth is gradually being lost, “spent upon vegetation and putrefaction, and converted into dry earth.… The fluids, if they are not supplied from without, must be in a continual decrease, and quite fail at last.” Newton seems to have believed that the Earth’s oceans are of cometary origin, and that life is possible only because cometary matter falls upon our planet. In a mystical reverie, he went still further: “I suspect, moreover, that it is chiefly from the comets that spirit comes, which is indeed the smallest but the most subtle and useful part of our air, and so much required to sustain the life of all things with us.”
As early as 1868 the astronomer William Huggins found an identity between some features in the spectrum of a comet and the spectrum of natural or “olefiant” gas. Huggins had found organic matter in the comets; in subsequent years cyanogen, CN, consisting of a carbon and a nitrogen atom, the molecular fragment that makes cyanides, was identified in the tails of comets. When the Earth was about to pass through the tail of Halley’s Comet in 1910, many people panicked. They overlooked the fact that the tail of a comet is extravagantly diffuse: the actual danger from the poison in a comet’s tail is far less than the danger, even in 1910, from industrial pollution in large cities.
But that reassured almost no one. For example, headlines in the San Francisco Chronicle for May 15, 1910, include “Comet Camera as Big as a House,” “Comet Comes and Husband Reforms,” “Comet Parties Now Fad in New York.” The Los Angeles Examiner adopted a light mood: “Say! Has That Comet Cyanogened You Yet?… Entire Human Race Due for Free Gaseous Bath,” “Expect ‘High Jinks,’ ” “Many Feel Cyanogen Tang,” “Victim Climbs Trees, Tries to Phone Comet.” In 1910 there were parties, making merry before the world ended of cyanogen pollution. Entrepreneurs hawked anti-comet pills and gas masks, the latter an eerie premonition of the battlefields of World War I.
Some confusion about comets continues to our own time. In 1957, I was a graduate student at the University of Chicago’s Yerkes Observatory. Alone in the observatory late one night, I heard the telephone ring persistently. When I answered, a voice, betraying a well-advanced state of inebriation, said, “Lemme talk to a shtrominer.” “Can I help you?” “Well, see, we’re havin’ this garden party out here in Wilmette, and there’s somethin’ in the sky. The funny part is, though, if you look straight at it, it goes away. But if you don’t look at it, there it is.” The most sensitive part of the retina is not at the center of the field of view. You can see faint stars and other objects by averting your vision slightly. I knew that, barely visible in the sky at this time, was a newly discovered comet called Arend-Roland. So I told him that he was probably looking at a comet. There was a long pause, followed by the query: “Wash’ a comet?