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The theory of cometary panspermia is reviewed in relation to evidence from astronomy, biology and recent studies of meteorites. The spectroscopic signatures in interstellar material within our galaxy and in external galaxies that have been known for many years most plausibly represent evidence for the detritus of life existing on a cosmic scale. Such spectral features discovered in galaxies of high redshift points to life arising at a very early stage in the history of the Universe. Evidence of fossils of microscopic life forms in meteorites that have been discussed over several decades, and augmented recently with new data, reaffirms the case for cometary panspermia.

Within the solar system, approximate realizations of the three-body problem occur when a comet approaches a planet while being affected mainly by such a planet and the Sun, and this configuration was investigated by Tisserand within the framework of Newtonian gravity. The exact relativistic treatment of the problem is not an easy task, but this paper develops an approximate calculational scheme which computes for the first time the tiny effective-gravity correction to the equation of the surface for all points of which it is equally advantageous to regard the heliocentric motion as being perturbed by the attraction of Jupiter, or the jovicentric motion as being perturbed by the attraction of the Sun. This analysis completes the previous theoretical investigations of effective-gravity corrections to the Newtonian analysis of three-body systems, and represents an intermediate step towards relativistic effects on cometary motions.

The importance of distinguishing between hypotheses that are verified by a vast number of predictions and have not been falsified, and conjectures without any compelling evidence is of paramount importance for science educators to keep in mind. This article describes the trajectory of one such hypothesis. The concept of cometary panspermia has been developed over a period of four decades and evidence for it has straddled many scientific disciplines from astronomy, to geology, biology and epidemiology. With an ever-increasing number of predictions of this theory being verified, the question as to why it has not entered mainstream thinking is an intriguing one. I suggest that this resistance is connected with sociological considerations, including a deep cultural hostility to theories that appear to have a foreign or “alien” provenance.

The theory of cometary panspermia is reviewed in relation to evidence from astronomy, biology, and recent studies of meteorites. The spectroscopic signatures in interstellar material within our galaxy and in external galaxies that have been known for many years most plausibly represent evidence for the detritus of life existing on a cosmic scale. Such spectral features discovered in galaxies of high redshift points to life arising at a very early stage in the history of the Universe. Evidence of fossils of microscopic life forms in meteorites that have been discussed over several decades, and augmented recently with new data, reaffirms the case for cometary panspermia.

With the many major advances in medical and biological sciences that have taken place in recent years it would seem remarkable that we are still unable to come to grips with the problem of influenza. In spite of our ability to produce detail sequences of bacterial and viral genomes, the emergence of new epidemic or pandemic strains of the influenza virus is still shrouded in mystery. To resolve this mystery we may need to turn to space.

Panspermia theories require the transport of micro-organisms in a viable form from one astronomical location to another. The evidence of material ejection from planetary surfaces, of dynamical orbit evolution and of potential survival on landing is setting a firm basis for interplanetary panspermia. Pathways for interstellar panspermia are less clear. We compare the direct route, whereby life-bearing planetary ejecta exit the solar system and risk radiation hazards en route to nearby stellar systems, and an indirect route whereby ejecta hitch a ride within the shielded environment of comets of the Edgeworth- Kuiper Belt that are subsequently expelled from the solar system. We identify solutions to the delivery problem. Delivery to fully-fledged planetary systems of either the direct ejecta or the ejecta borne by comets depends on dynamical capture and is of very low efficiency. However, delivery into a proto-planetary disc of an early solar-type nebula and into pre-stellar molecular clouds is effective, because the solid grains efficiently sputter the incoming material in hypervelocity collisions. The total mass of terrestrial fertile material delivered to nearby pre-stellar systems as the solar system moves through the galaxy is from kilogrammes up to a tonne. Subject to further study of bio-viability under irradiation and fragmenting collisions, a few kg of original grains and sputtered fragments could be sufficient to seed the planetary system with a wide range of solar system micro-organisms.

This essay traces the progress towards establishing panspermia as a new paradigm from the time of its last revival in the late 1970's to the year 2002. Many lines of evidence are seen to converge on the hypothesis that life is a cosmic phenomenon.

It is nearly 30 years since the first decisive evidence of microbial morphologies in carbonaceous chondrites was discovered and reported by Hans Dieter Pflug. In addition to morphology other data, notably laser mass spectroscopy, served to confirm the identification of such structures as putative bacterial fossils. Recent examinations of cometary dust collected in the stratosphere and further studies of carbonaceous meteorites reaffirm the presence of putative microbial fossils. Since carbonaceous chondrites (particularly Type 1 chondrites) are thought to be extinct comets the data reviewed in this article provide strong support for theories of cometary panspermia.

Cycles of glaciation with an average period of ~100 kyr are mediated by impacts of cometary bolides. Ice-age conditions are dry and dusty with low rates of precipitation. Comets in the mass range 10¹⁵–10¹⁶ g impacting the oceans could release enough water vapour into the atmosphere to enhance a depleted greenhouse effect. The energy deposited in the oceans would also warm the surface layers, thus starting up an evaporation-precipitation cycle which ushers in warmer interglacial interludes. The latter have neutral stability and are necessarily short-lived, eventually drifting back to glacial conditions on timescales of ~10 kyr.

Liquid water in comets, once considered impossible, now appears to be almost certain. New evidence has come from the discovery of clay minerals in comet Tempel 1, which complements the indirect evidence in aqueous alteration of carbonaceous chondrites. Infrared spectral indication of clay is confirmed by modelling data in the 8–40 μm and 8–12 μm wavebands on the basis of mixtures of clays and organics. Radiogenic heating producing liquid water cores in freshly formed comets appears more likely on current evidence for solar system formation. A second possibility investigated here is transient melting in comets in the inner solar system, where thin crusts of asphalt-like material, formed due to solar processing and becoming hot in the daytime, can cause melting of sub-surface icy material a few centimetres deep. Supposing comets were seeded with microbes at the time of their formation from pre-solar material, there would be plenty of time for exponential amplification and evolution within the liquid interior and in the transient ponds or lakes formed as the outer layers are stripped away via sublimation.

Panspermia, an ancient idea, posits that microbial life is ubiquitous in the Universe. After several decades of almost irrational rejection, panspermia is at last coming to be regarded as a serious contender for the beginnings of life on our planet. Astronomical data is shown to be consistent with the widespread distribution of complex organic molecules and dust particles that may have a biological provenance. A minuscule (10⁻²¹) survival rate of freeze-dried bacteria in space is all that is needed to ensure the continual recycling of cosmic microbial life in the galaxy. Evidence that terrestrial life may have come from elsewhere in the solar system has accumulated over the past decade. Mars is seen by some as a possible source of terrestrial life, but some hundreds of billions of comets that enveloped the entire solar system, are a far more likely primordial reservoir of life. Comets would then have seeded Earth, Mars, and indeed all other habitable planetary bodies in the inner regions of the solar system. The implications of this point of view, which was developed in conjunction with the late Sir Fred Hoyle since the 1970's, are now becoming amenable to direct empirical test by studies of pristine organic material in the stratosphere. The ancient theory of panspermia may be on the verge of vindication, in which case the entire universe would be a grand crucible of cryomicrobiology.

Mechanisms of interstellar panspermia have recently been identified whereby life, wherever it has originated, will disperse throughout the habitable zone of the Galaxy within a few billion years. This re-opens the question of where life originated. The interiors of comets, during their aqueous phase, seem to provide environments no less favourable for the origin of life than that of the early Earth. Their combined mass throughout the Galaxy overwhelms that of suitable terrestrial environments by about 20 powers of ten, while the lifetimes of friendly prebiotic environments within them exceeds that of localised terrestrial regions by another four or five powers of ten. We propose that the totality of comets around G-dwarf Sun-like stars offers an incomparably more probable setting for the origin of life than any that was available on the early Earth.

We report on the physical, chemical and mineral properties of a series of stone fragments recovered from the North Central Province of Sri Lanka following a witnessed fireball event on 29 December 2012. The stones exhibit highly porous poikilitic textures comprising of isotropic silica-rich/plagioclase-like hosts. Inclusions range in size and shape from mm-sized to smaller subangular grains frequently more fractured than the surrounding host and include ilmenite, olivine (fayalitic), quartz and accessory zircon. Bulk mineral compositions include accessory cristobalite, hercynite, anorthite, wuestite, albite, anorthoclase and the high pressure olivine polymorph wadsleyite, suggesting previous endurance of a shock pressure of ~20GPa. Further evidence of shock is confirmed by theconversion of all plagioclase to maskelynite. Here the infrared absorption spectra in the region 580 cm⁻¹ to 380 cm⁻¹ due to the Si-O-Si or Si-O-Al absorption band shows a partial shift in the peak at 380 cm⁻¹ towards 480 cm⁻¹ indicating an intermediate position between crystalline and amorphous phase. Host matrix chemical compositions vary between samples, but all are rich in SiO₂. Silica-rich melts display a heterogeneous K-enrichment comparable to that reported in a range of nonterrestrial material from rare iron meteorites to LL chondritic breccias and Lunar granites. Bulk chemical compositions of plagioclase-like samples are comparable to reported data e.g. Miller Ranger 05035 (Lunar), while Si-rich samples accord well with mafic and felsic glasses reported in NWA 1664 (Howardite)as well asdata for fusion crust present in a variety of meteoritic samples.Triple oxygen isotope results show Δ¹⁷O = .0.335 with δ¹⁸O (‰ rel. SMOW) values of 17.816 ± 0.100 and compare well with those of known CI chondrites and are within the range of CI-like (Meta-C) chondrites. Rare earth elemental abundances show a profound Europium anomaly of between 0.7 and 0.9 ppm while CI normalized REE patterns accord well with those of high potassium and high aluminium glasses found in lunar and 4 Vesta samples. Two-element discrimination maps of FeO vs SiO₂, FeO vs TiO₂, FeO vs Al₂O₃ and FeO vs Na₂O similarly match those of impact glasses present in lunar samples and remain within relatively close proximity of the KREEP component. Iridium levels of between 1–7ppm, approximately 10⁴ times that of terrestrial crustal rocks, were detected in all samples.

Recent observations of Halley's Comet show a broad absorption band centred at 3.4 μm and which can be explained on the basis of a bacterial grain model.

The recently reported extreme redness of a class of Kuiper-belt objects could be yet another indirect indication of extraterrestrial microbiology in the outer solar system.

X-ray fluxes observed from comet C/1996 B2 (Hyakutake) are readily explained in terms of scattering by carbonaceous particles with radii of several tens of Angstroms. A few tenths of a megatonne of such particles appear to have been present in the cometary coma on March 26–28, 1996.

We discuss evidence to support a component of vertical (rather than horizontal) transmission in the propagation of pandemic influenza.

The arguments in support of life as a cosmic phenomenon are not readily accepted by a culture in which a geocentric theory of biology is seen as the norm.

Chemoautotrophic microorganisms were able to replicate and evolve in the interiors of some 10¹¹ cometary bodies that occupied the outer regions of the solar system some 4 billion years ago. The requirement of a liquid condition within comets was maintained for an initial epoch through the energy released in radioactive decays. When such energy sources eventually became exhausted inward freezing led to the production of multi-cracked, fragile cometary structures.

There exists a close correspondence between the measured infrared properties of diatoms and the infrared spectrum of interstellar dust as observed in the Trapezium nebula and toward the galactic center source GC-IRS 7. Diatoms and bacteria also exhibit an absorbance peak near 2200 Å, which is found to agree with the observed ultraviolet absorbance properties of interstellar grains. We review the observational data and consider the known properties of diatoms and bacteria. It is suggested that these characteristics are consistent with the concept of a cosmic microbiological system in which these or similar microorganisms might exist on comets, Europa and in interstellar space.