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COMETS AND CATASTROPHES
• Kohoutek's visit
• Urey on cometary cataclysms
• Comets and oil formation
• Vsekhsvyatskii's views on the origin of comets
During the latter half of January, 1974, in the evening sky, a comet will emerge from behind the sun. Named Kohoutek after its discoverer, this comet--after first passing 14 million miles from the sun--will approach within about 75 million miles of the earth in mid-January. Earlier, in December, it may be visible in the morning sky, and during both months there is a chance it will be visible during daylight hours.
While comets tend to be unpredictable, especially so far as their brightness goes, the claims for Comet Kohoutek have been optimistic. Brian G. Marsden, astronomer and director of the Central Bureau for Astronomical Telegrams, Smithsonian Astrophysical Observatory, told us: "There's every possibility that this could be the best comet of the century. It is unprecedented that we have known about a potentially bright comet so long ahead of time" --usually they are discovered only a month or two before they become bright. Nevertheless, Marsden does not rule out the alternative that Kohoutek might "fizzle out," failing, visually, to perform as expected.
Whatever its performance, scientists are gearing up to learn what they can from this cosmic interloper. There is talk about observation from space probes and from Skylab. The comet's interaction with the solar wind will be investigated, and it is hoped that its close approach to the sun will make detailed spectral analyses possible. After all, remarked Marsden, "We really don't know what a comet is."
UREY'S CATASTROPHIC VIEWS
Only a few weeks before the Smithsonian's telegram announcing the discovery of Comet Kohoutek, there appeared in Nature, 242 (March 2, 1973, P. 32) a letter on "Cometary Collisions and Geological Periods" by Professor Harold Urey, who claims there that repeated comet-Earth collisions have been responsible, not only for the tektites scattered over Earth's surface, but also for the catastrophic breaks between major geological periods. He cites as possible effects of these collisions "great variation in climatic conditions," "great seismic effects," "extensive lava flows," and the "scattering of ocean water over land areas." Many animal and plant types must have become extinct. "It does seem possible and even probable," writes Urey, "that a comet collision with the Earth destroyed the dinosaurs and initiated the Tertiary division of geologic time."
So Urey offers a set of data which, to his mind, calls for a catastrophic interpretation. And, needless to say, he does not acknowledge either H. H. Nininger's (Out of the Sky, 1952, Dover reprint, 1959, p. 294) or Velikovsky's priority in attributing major geological upheavals and the extinction of many forms of life to the catastrophic approach of celestial bodies. Further, he illustrates that a catastrophic hypothesis may now be set forth in an established journal of science--at least by a Nobel prizewinner, providing that the proposed cataclysms occurred so far in the past (or so far in the future: "It will most probably be millions of years before the next collision occurs") as not indecently to unsettle our faith in the clockwork stability of the solar system throughout human history.
We may observe one note of irony: Urey's discussion of cometary collisions is highly speculative. Yet, no subsequent issues of Nature has carried even one violent attack on him for being so "unscientific" as to state, without positive evidence, that a cometary collision "probably" caused the extinction of the dinosaurs.
THE ORIGIN OF PETROLEUM
Urey's letter has a bearing on the question raised by Angino (Pensee, winter, 1973, 47): "Velikovsky and A. T. Wilson have both said that the petroleum came as rain from above. While this is open to discussion, the fact of the matter still is that the chemistry of petroleum found in recent sediments . . . and that found in ancient sediments are not the same. One would still have to explain the ways in which each of the differences are brought about. It is possible under Velikovsky's thesis that there have been other rains of petroleum, but I find it rather difficult to believe that such a repeat of circumstances occurs frequently in geological time."
As we have seen, Urey now supports Velikovsky's contention that extraterrestrially caused upheavals have rocked the Earth throughout geological time. In discussing the speculation that microtektites found on the Earth may have resulted from cometary impacts, Kellner and Yabushita (Nature, 235, 1972, 383) questioned the probability of such encounters. Durrani answered (Nature, 235, 1972, 383) them by citing Urey, Russel, and Kopal to the effect that one Earth-comet encounter every 35 million years is a low estimate. He then noted that, based on such an estimate, it is not extremely improbable that there may actually have been as many as four encounters during the last 35 million years.
Petroleum may have been formed during many of these events by a process such as that proposed by Oro and Han (Science, 153, 1966, 1393): "aromatic hydrocarbons and other organic compounds may have been formed as a result of collisions of comets with planets or satellites such as the moon and collisions of large meteorites with planets containing reducing atmospheres."
Some of the petroleum from the Venus encounter may have originated on Jupiter. W. F. Libby has suggested (seminar at University of Houston, July 12, 1966) that "oil" is raining on Jupiter, and Oro and Han cite the possibility that petroleum is now being formed in localized areas of Jupiter. D. M. Hunten, in his recent paper, "The Atmosphere of Titan" (Comments on Modern Physics, Part C, Vol. 4, No. 5, 149-55), remarked on the "likely presence of gasoline, kerosene, and tar" on the Saturnian satellite. "One can readily imagine a deep layer of tar covering the surface."
We might also take note of the fact that L. P. Gaucher, writing in Chemical Technology , argues that the Earth must have received continual rains of oil early in its history, owing to chemical reactions in the primitive atmosphere. When asked how he would account for variations in the composition of crude oil, Gaucher replied: "The oil could have been changed by local bacterial action and slow chemical reaction with surroundings, as well as by physical processes" (Intellectual Digest, March, 1973, 38).
VSEKHSVYATSKII ON COMETS
Astronomer S. K. Vsekhsvyatskii (director, Kiev Observatory) has explored the possibility that comets are created by ejection from the larger planets. This view, first broached in modern times by Lagrange and then developed by Proctor and Crommelin, has been given viable scientific status through Vsekhsvyatskii's 40 years of research. In the early 1930's he explained the orbital characteristics of short period comets on the basis of this ejection theory (Astron. J. USSR, 10, 1933, 37; 11, 1934, 450). Later Woerkom, having examined kinematic consequences of the ejection theory, expressed his "agreement with Vsekhsvyatskii that in this way almost all properties of short-period comets can be explained" (Bull. Astron. Inst. Netherlands, 1948, 399).
In 1967 Vsekhsvyatskii published an article describing portions of his previous work and presenting additional evidence for the theory (Soviet Astronomy, 11, no. 3, 1967, 473). In this article, "New Evidence for the Eruptive Origin of Comets and Meteoritic Matter," Vsekhsvyatskii notes that the arguments for the eruption of comets from Jupiter have not been debated despite their persuasiveness. Most current hypotheses depend on an assumption about condensation of the planets, satellites and comets from some type of primordial material. This assumption, accepted by tradition, "is in striking conflict with processes observed to take place on a grand scale in the world of galaxies and the world of stars," where decay and disintegration are observed.
(Comets themselves offer a fascinating example of such disintegration. According to Harvard astronomer Fred Whipple in the October, 1972, Astronautics and Aeronautics: "The Orbiting Astronomical Observatory and other space probes have demonstrated an enormous ejection of hydrogen and OH from three comets. The brightest, Comet Bennett (1970 II), comparable to Halley's famous comet, ejected hydrogen at a rate corresponding to 40 tons of water per second, according to A. D. Code and B. D. Savage. This adds up to a good fraction of a cubic kilometer of H20 during the passage of the comet about the sun." Writes E. Roemer (The Moon, Meteorites and Comets, ed. by Middlehurst and Kuiper, 1963, P. 540): "Most astronomers believe that the average lifetimes of comets are to be measured in thousands of revolutions, but some consider that comets disintegrate much more rapidly.")
Many hypotheses concerning comet origin also explicitly or implicitly assume that comets differ radically from bodies such as meteorites and asteroids. (This was a common argument raised by reviewers who derided Worlds in Collision in 1950.) Vsekhsvyatskii mentions two of the more recent discoveries which cast doubt on this assumption: Comet Ikeya-Seki (1965), passing through the sun's inner corona, exhibited a spectrum analogous to that of meteoritic material. At other times, when the vaporization processes were subdued, the comet emitted the common cyanogen-carbon spectrum. Second, Comet Ikeya of 1964 exhibited a carbon-13 to carbon-12 ratio consistent with values known or expected for planets.
Vsekhsvyatskii then points out the contradiction in current cosmogonies which propose that comets are supposed to have condensed as a result of collisions, whereas meteoritic matter and meteorites resulted from the destruction of surfaces because of the same collisions. Also he mentions that there is no explanation in condensation theories for the presence of complex hydrocarbon compounds in comet nuclei.
Vsekhsvyatskii plots the distribution of all known comets against the logarithm of their periods. A comparison with the distribution near the parabolic limit derived from Oort's data demonstrates the absence of a steady state in the system of comets, thereby excluding uniformitarian capture models.
(Incidentally, capture models often assume that comets originate somewhere outside the solar system and are attracted by the sun's gravitational field. Perturbations of the comets by Jupiter are thought to create orbital characteristics for the comets such that they are captured in orbits around the sun. But Chao-Ho-Sung (Ph. D. thesis, Yale University, 1969) contends that comets cannot be permanently captured by this process unless non-gravitational forces are in effect.)
A display of the distribution of inclinations of cometary orbits grouped according to periods reveals a regular change from a purely planetary type of motion--that is, motion in the plane of the planetary orbits--for Jupiter's group to a nearly symmetrical distribution with respect to inclinations for the long-period comets. Vsekhsvyatskii demonstrated as early as 1952 that this is a necessary consequence of the eruption theory. The absence of short period comets with retrograde motion and the evidence for substantial disintegration rates of these comets also suggest a recent eruptive origin. Further, Vsekhsvyatskii notes the remarkable fact that the closest approaches between comets and Jupiter usually occur either 0.5 or 1.5 revolution prior to discovery of the comets. This suggests the possibility that these comets originate from Jupiter.
In a previous paper Vsekhsvyatskii had shown that periods of sharp decline in Jupiter's brightness are associated with the appearance of clouds of what could be volcanic ash above the planet's cloud cover. In the 1967 paper he draws attention to the correlation between these periods of brightness-reduction and the appearance of new comets. Particularly noteworthy cases include the bursts of Jovian activity during 1872-1888, 1910-1920, and 1961-1965. The first period is associated with the appearance of the bright Comets Wolf 1 and Brooks 2 and the discovery of four other comets, and the second period is associated with the development of a whole series of comets. Most notable is the third period of activity, during which the new Comets 1963 VII (Kearns-Kwee), 1965b (Tsuchinshan 1), and 1965c (Tsuchinshan 2) emerged nearly simultaneously from Jupiter's sphere of influence.
Vsekhsvyatskii does some encounter-probability analysis to answer specific questions about the capture theory, concluding that observed cometary orbital properties show no similarity to what is predicted by the capture theory. And on the basis of calculations concerning the total mass loss of the planets during the lifetime of the solar system, Vsekhsvyatskii suggests that the low mean density of Saturn might be associated with an especially high level of eruptive activity, and that vast cataclysms of this type could have led to the formation of the rings.
Finally, we are justified in remarking that Velikovsky's research into the observations of the ancients adds further support to Vsekhsvyatskii's eruptive theory, while the latter gives greater theoretical strength to Velikovsky's conclusions. Indeed, it is not inconceivable that this fact largely accounts for the continuing reluctance of western astronomers to dignify Vsekhsvyatskii's conclusions with debate and analysis.
PENSEE Journal V