Comet formation in molecular clouds

The observed properties of the long-period comet system, and its periodic disturbance by galactic forces manifesting as terrestrial impact episodes, may be indicative of a comet capture/escape cycle as the Solar System orbits the Galaxy. A mean number density of comets in molecular clouds of ～10^?1±1 AU^?3 is implied. This is sufficient to deplete metals from the gaseous component of the interstellar medium, as observed, but leads to the problem of how stars are formed nevertheless with solar metal abundances. Formation of comets prior to stars in dense systems of near-zero energy may be indicated, and isotope signatures in cometary particles may be diagnostic of conditions in young spiral arm material.     

Evolution, punctuational crises and the threat to civilization

The relationship between “punctuated equilibrium” and “impact crises” is critically examined in the light of our present knowledge of asteroids and comets. It turns out that the emphasis on relatively narrow epochs associated with occasional “NEO” impacts is probably misplaced. Rather priority should be given to the wider and more frequent epochs associated with multiple “NEO” debris impacts which result in so-called “punctuational crises” afflicting the planets. These comprise the global coolings, super-Tunguska events and generally enhanced fireball flux produced by the larger orbital debris whenever an active, dormant or dead comet fragments and produces a trail. Taken as a whole and in conjunction with the target, the response function is inevitably complex. Nevertheless we broadly expect that the strength of a punctuational crisis will vary as the progenitor comet mass, the inverse dispersion of its debris and the inverse delay since fragmentation. The encounter of P/SL-9 with Jupiter may be taken as representing an extreme punctuational crisis where the dispersion and delay were exceptionally small. The more familiar crises affecting the Earth with less extreme values of dispersion and delay, which have resulted in civilization being disturbed a good many times during recent millennia, are no less important however. Indeed, the next such threat to civilization ostensibly has a roughly 1 in 4 lifetime chance. Any support for the Spaceguard programme which detracts from consideration of these punctuational crises, whatever their strength, would seem now to be peculiarly wide of the mark.     

The expansion of our galaxy

The reasons for regarding our galaxy as a rapidly expanding spiral system are presented. The observed structure suggests ejection from a rotating nucleus.     

The origin of gravity

It has been shown by Atkinson (1965) that there is a rigorously exact euclidean interpretation of the general relativity field equations if certain arbitrary definitions of mass (m0 and the velocity of light (c) are invoked. With a preferred (euclidean) frame postulatedab initio, a particularly simple explanation in terms of classical physics may be found for very similar definitions ofm andc. It is not unexpected that with this scheme, all the usual tests of general relativity (light deflexion, perihelion motion, gravitational redshift, and radar delay time) are immediately satisfield. The preferred frame is however identified with a real aether and this requires a return to the Lorentzian interpretation of the special relativistic transformations of space and time variables. It is shown that gravity may be attributed to the action of a temperature gradient in the aether and an explanation of its origin in terms of an ideal relativistic gas is proposed. The temperature gradients are thermodynamically stable and do not diffuse if the relativistic aether ( _A ) is effectively adiabatic and matter is fundamentally a species of aether with instantaneous motion at high (> _A ) relative to the aethereal reast frame. To be consistent with such a picture, it is necessary to assume aether particles are capable of forming temporary associations (not recognized as matter) which take on some of the properties of crystalline solids and thereby become the means of transmitting electromagnetic radiation through space. The aether is essentially treated as a virtually incompressible fluid in which the pressure at any point arises from both random (temperature) and bulk (high ) motions. A number of specific predictions arising from this theory of gravity are indicated and these may serve to discriminate it from general relativity.     

Evolution, punctuational crises and the threat to civilization

The relationship between punctuated equilibrium and impact crises is critically examined in the light of our present knowledge of asteroids and comets. It turns out that the emphasis on relatively narrow epochs associated with occasional NEO impacts is probably misplaced. Rather priority should be given to the wider and more frequent epochs associated with multiple NEO debris impacts which result in so-called punctuational crises afflicting the planets. These comprise the global coolings, super-Tunguska events and generally enhanced fireball flux produced by the larger orbital debris whenever an active, dormant or dead comet fragments and produces a trail. Taken as a whole and in conjunction with the target, the response function is inevitably complex. Nevertheless we broadly expect that the strength of a punctuational crisis will vary as the progenitor comet mass, the inverse dispersion of its debris and the inverse delay since fragmentation. The encounter of P/SL-9 with Jupiter may be taken as representing an extreme punctuational crisis where the dispersion and delay were exceptionally small. The more familiar crises affecting the Earth with less extreme values of dispersion and delay, which have resulted in civilization being disturbed a good many times during recent millennia, are no less important however. Indeed, the next such threat to civilization ostensibly has a roughly 1 in 4 lifetime chance. Any support for the Spaceguard programme which detracts from consideration of these punctuational crises, whatever their strength, would seem now to be peculiarly wide of the mark.     

Towards a Dynamical History of ‘Proto-Encke‘

There are too few active comets to account for the observed zodiacal dust. Rather we look to the collisional fragmentation and erosion of sub-kilometre meteoroids in orbit close to the ecliptic. Since 1975 we have also been aware of an apparently massive meteoroidal swarm in probable 7:2 mean motion resonance with Jupiter, seemingly at the heart of the Taurid Complex and connecting therefore with the near-ecliptic system through the so-called Štohl Stream. The notable absence of pre-1786 apparitions of 2P/Encke took on a new significance with the 1983 detection by IRAS of its asymmetric trail inside this resonance. Thus it was possible all these meteoroidal components were ultimately derived from a continuously eroded, substantially dormant, librating progenitor within the trail whose more volatile inclusions are exposed from time to time and expelled either singly or severally as independent comets. A Taurid progenitor of this kind (proto-Encke) dominating the inner Solar System environment probably then accounts for most of the recorded enhancements of the larger meteoroid flux to Earth, including ‘Tunguska’ bodies as well. Terrestrial dust insertions which control mean temperature and hence climate are also inferred based upon the libration and nodal precession half-periods of proto-Encke (∼0.2 kyr, ∼2.5 kyr respectively) albeit the longer of these cycles was not at first evident in the terrestrial record (Asher & Clube 1993). Recently however this cycle appears to have been confirmed as a significant (long term) global warming/meridional atmospheric circulation / iceberg calving cycle with the correct phase producing the so-called mini-Heinrich and Heinrich events of the Holocene and late Upper Pleistocene respectively, i.e., during the past ∼60 kyr BP. The comparative stability of this terrestrial cycle, in contrast with the weakness of the observed resonance, suggests a fairly recent diversion therefore from a much stronger sungrazing 7:2 Jovian resonance in which proto-Encke's and Jupiter's longitudes of perihelion are related by ϖ pE ≈ ϖ J or ϖ J + π. Thus both the Hephaistos Stream and the Taurid Complex could have formed together during a recent close planetary encounter, say with Mercury ∼5 kyr BP. It follows that we envisage a single large progenitor in 7:2 Jovian sungrazing resonance for 50 kyr or so which undergoes repeated tidal stress: a continuous dust-induced major glaciation is thus sustained on Earth for most of this dynamical timescale before a disruptive planetgrazing event finally brings its sungrazing status to an end and produces the present meteoroidal complex. This evolutionary sequence almost certainly requires that the original sungrazing stream still exists (without its source): a potentially significant fact because it may have a direct bearing on both the observed zodiacal bands and the original progenitor orbit as well as the known periodic variation of solar radiance and convected magnetic field, of possible relevance to the solar cycle. While these aspects have to be further explored, the purpose of the present investigation is to describe some preliminary modelling with a view to inferring the likely dynamical history of proto-Encke. This revised version was published online in July 2006 with corrections to the Cover Date.     

The fundamental role of giant comets in earth history

We discuss some fundamental aspects of Earth history as predicted by what has come to be called coherent rather than stochastic catastrophism. The latter essentially seeks to provide an understanding of terrestrial evolution in terms of occasional kilometre-plus impactors from the asteroid belt whereas the former recognises a far more complex extraterrestrial regime arising from the streams of sub-kilometre and kilometre-plus debris due to the disintegration of successive giant comets in sub-Jovian orbits. Periodicities of 15 Myr during the later Phanerozoic (i.e. 250 to 0 Myr BP) and 200 yr during the Holocene (i.e. 10,000 to 0 yr 1313) are likely fundamental signatures in the terrestrial record relating to the action of past and present giant cornets respectively.     

An exceptional cosmic influence and its bearing on the evolution of human culture as evident in the apparent early development of mathematics and astronomy

The proposal that cometary dust particles play a significant role in the emergence and evolution of both life and disease on suitable planets was first made some 25 years ago by Hoyle and Wickramasinghe. Fundamental to this proposal was a process of punctuated seeding by particular (bio)chemical species believed to originate naturally and predominantly in larger comets, say those with diameters greater than about 100 kilometres. Rather less well known is a parallel proposal likewise favoured by Hoyle that a particular giant comet, the most recent to settle in cis-Jovian space, accounting for the latest significant phase of evolution on Earth, also had a significant part to play in the cultivation by homo sapiens of its civilization and culture. Such proposals may be seen by many as examples of excessively lateral thinking but they by no means lack independent support and have important implications for the otherwise uncertain origin of the latest ice-age (basic to climatology) and for the otherwise uncertain generation of early calendars (basic to the management of society). Aspects of these proposals are considered here in relation to a much respected supposedly Chaldean calendar probably passed down by the dynastic Isins (also the Essenes?) which evidently bears witness to known early mathematical and astronomical skills but which largely ceased to be available to subsequent scholarship beyond the Early Christians (ca. 100 CE) pending its (recent) recovery through the medium of Dead Sea Scrolls.