Comets and life 4

Updating Comets and Magic Universe

Did comets spark life on Earth?

Part 4: Life footloose in space

In Part 1 of this series, I mentioned that in Comets, written 30 years ago, I made fun of propositions from the astrophysicists Fred Hoyle and Chandra Wickramasinghe about viable entities living in comets and being delivered ready-made to the Earth, scattered from the comets’ tails. What follows fulfils a promise to look at Chandra’s present ideas — I hope with an open mind.

To back-track a little, there’s a 100-year history of eminent scientists, driven by despair about explaining the very improbable chemistry of life by home cooking on the Earth, suggesting that life came from elsewhere. Of course, their scenarios didn’t explain the origin of life, they merely transferred it somewhere else. Out of sight, out of mind, perhaps.

  • 1907 Svante Arrhenius (yes, the CO2 warming pioneer) suggested that bacterial spores escaped from an alien planet, were driven through interstellar space by the pressure of sunlight, and revived when they reached the Earth.
  • 1971 Francis Crick (yes, of DNA fame) with Leslie Orgel proposed that intelligent beings in another part of the Galaxy spotted the Earth as a suitably wet planet and sent bacteria in a spaceship to seed it.
  • 1979 Fred Hoyle (yes, celebrated for the origin of the elements) with Chandra Wickramasinghe said that life on Earth began in comets, and diseases still come from them.

It was hard not to chuckle over their book Diseases from Space, because Hoyle and Wickramasinghe’s account filled the sky with germs, in a distant echo of the old superstition that comets portended plagues.

John Gadbury (1665) linked comets and catastrophes -- "Famine, Plague & Warrs" In actuality, bubonic plague afflicted London following the depicted 1664-5 comet. Obtained from the Royal Astronomical Society, this is an illustration in N. Calder, Comets: Speculation and Discovery.

From Comets (Nigel Calder, first published in 1980)

As the two astrophysicists portray diseases from outer space, they are a straightforward extension, and a daily confirmation, of the origin of life in comets. If comets could seed our planet with viruses and bacteria four billion years ago, why not now? If a millionth part of the meteoritic debris falling to the Earth from comets consists of viruses, a small garden could collect millions of viruses every day, ready to assail plants, pets and humans. Hoyle and Wickramasinghe imagine the various diseases that afflict mankind originating in different comets.

Wickramasinghe and Hoyle, as pictured on the jacket of A Journey with Fred Hoyle. See reference.

They are not suggesting anything as vulgar as a direct link between sightings of comets and outbreaks of disease. The danger they perceive lies in the invisible clouds of dust spewing out of comets, orbiting through the inner Solar System, and being scattered and smeared through space in very complex ways. When the Earth runs into a cloud, the germs that survive the encounter settle to the ground only slowly, while weather patterns spread them and re-clump them around the world. Once they are well established on the Earth, some diseases need no replenishment from space: tuberculosis is one. Others, polio and cholera for instance, persist of their own accord but are ‘topped up’ by fresh deliveries of germs from space. Finally, in this unwholesome catalogue, there are diseases like bubonic plague and smallpox that come and go as the orbiting clouds decree. Hoyle and Wickramasinghe affirm: ‘We did not arrive at our ideas at all lightheartedly. ‘

That I believe: I have never seen Fred Hoyle in a merry mood, and who would want to jest about diseases – even influenza, which he singles out for special attention? To illustrate the patchy, sudden and widespread outbreaks that the theory requires, he cites the fatally virulent strain of influenza that first struck at human beings in Massachusetts in September 1918 and, within a couple of days, felled others in Bombay. That was before the days of intercontinental air travel. the advent of which, according to Hoyle, has had little effect on the rate of spread of influenza. Epidemiologists would explain the near-simultaneous outbreaks in the USA and India by viruses harboured among animals and spread in advance around the world by birds and domestic animals. But Hoyle scoffs at such mundane explanations: influenza, he says, appears to exist in humans only to the extent that it is ‘driven from the outside’.

The old British custom of isolating children in boarding schools provided a special opportunity for testing the hypothesis that diseases come from comets. Hoyle and Wickramasinghe were not content to comb the medical literature for mysteries that they might turn to their advantage. Like good scientists they formulated a prediction: that any new outbreak of influenza would be very patchy. An epidemic in the winter of 1977-78 gave them the opportunity they needed, and the boarding schools had precise information on where pupils slept and on who contracted the ‘flu when. The result was that the first book on medical astromicrobiology, Hoyle and Wickramasinghe’s Diseases from Space (1979), was decorated with plans of schools and dormitories, like one of the more complicated detective novels.

And from the tribulations of the adolescent upper crust that winter they proved, to their own satisfaction at least, that’ flu was not communicated from person to person and was even more patchy than they predicted. For example at Eton College one third of the boys were taken ill while St George’s College, situated just a few hundred metres away and sharing the same medical officer, had no influenza at all. The Eton boys slept in twenty-five different houses, but they mixed for teaching and to some extent for eating, yet the incidence of influenza ranged from a single case among seventy boys in one house, to levels well above the average in others.

The odds against these variations occurring by chance were rated by the astrophysicists as astronomical, and they offered a meteorological explanation for the fine-scale patchiness. The most effective viruses from outer space would be those washed down in raindrops that ‘dried out’ before they reached the ground, leaving the viruses to tumble down the rest of the way in local turbulence. The direction of the wind near the surface, interacting with topography and buildings, could greatly affect the patterns of turbulence, creating fortunate spots that escaped the virus.

It is unhealthy to go out of doors – that is an obvious deduction from evidence of this kind, and the theory in general. A tragic example is said to have been the Legionnaires’ disease of 1976. Some members of the American Legion just stepped outside their hotel lobby in Philadelphia to watch a parade go by and were zapped by a small comet-cloud carrying a previously unrecognised bacillus. Twenty-nine failed to recover.

The particular suspicion that the comet Halley is responsible for influenza deserves a little elaboration. Hoyle and Wickramasinghe do not mean all variants of that disease but the two particular forms of the virus known to pathologists as H2/N2 and H3/N2: the first of these is Asian ‘flu, which struck world-wide in 1957, while the second was responsible for the pandemic of 1968. In both cases there was evidence that many people over about seventy-five years of age had immunity to the virus subtypes, implying that they had been infected in previous outbreaks – a figure that jibes conveniently with the seventy-six-year period of Halley in its orbit around the Sun. (Also, you may think, with human longevity.) As explained earlier, the comet did not have to be anywhere near the Earth in 1959 or 1968: only its ‘flu-laden clouds.

While you have a theory bubbling briskly on the front burner of the imagination, you may as well take care of the Mary Celeste, the Fall of the Roman Empire, and the Problem of Evil. Now as far as I know Hoyle and Wickramasinghe have not yet called down bugs from space to explain the disappearance of the entire crew from a well-found brig in mid-Atlantic, but they have no difficulty with the decline of Rome. During the period from AD 400 to 140 the earthlings had a particularly nasty time with the clouds of’ diseases spun off from the comets. A ‘disease-filled millennium’, they call it, and its onset forced people to live farther apart and thus to ‘uncivilise’ themselves; it also, so they say, moved the the Europeans to adopt the ‘sombre’ religion of Christianity.

As for the theological Problem of Evil, the apparently needless suffering from disease that God permits, it can be translated into a biological question. Why have we not evolved perfect immunity to infectious diseases? The answer given by the astrophysicists is that disease is necessary for major steps in evolution to occur, because organisms can incorporate novel hereditary messages from bacteria and viruses – not just mutant genes, but whole new sets of genetic material. Organisms that did not let the viruses in would stop evolving and soon become extinct. In this way the two authors make comets out to be a driving force throughout the history of life on Earth, and also attempt to disarm their medical critics who ask tetchily how viruses newly arriving from the depths of space know how to attack highly evolved animals like ourselves.

There was great rejoicing when the World Health Organization announced the elimination of smallpox from the Earth – the deadly and disfiguring disease that had scourged mankind since ancient times. But Hoyle and Wickramasinghe shake their heads gravely: they see an historical pattern in which smallpox comes and goes at intervals of several hundred years and declare that the evidence clearly points to smallpox coming from a cometary source.

Not even physiognomy escapes the astrophysicists’ attention. The human nose, they say, has evolved its shape, with nostrils opening downwards, because of the protection it gives against viruses falling out of the sky. This sets me thinking: it used to be supposed that comet watchers and other stargazers were especially at risk from wells, road works and open manholes. Now it seems that those who turn their faces to the sky are also undoing the careful work of natural selection and courting all kinds of horrible infections. Brain fever, too?

I kid you not, gentle reader. But that was 30 years ago and there was a lot of  unkind gossip at the time. Some suggested that, having been cheated of a Nobel Prize in physics that he richly deserved, for figuring out the origin of the elements, Fred Hoyle was hoping for the Nobel Prize in physiology or medicine.

Wickramasinghe’s latest opinions

Wickramasinghe's Fig. 1: Amplification cycle of cosmic biology. See ref. 2010 below.

Fred died in 2001 but Chandra, 24 years younger, remains active in Cardiff and just a couple of months ago he published a helpful update of his views on “The astrobiological case for our cosmic ancestry”. Whilst noting that the link to disease epidemics is “contentious”, Wickramasinghe is sturdily unrepentant about the notion that space is replete with bacteria.

As the full text is readily available (see References) I’ll just give some extracts and diagrams that seem to me to convey the essence of what he has to say.

… the ‘ life-cycle ’ of organic matter in the galaxy is shown schematically in Fig. 1. Life has started sometime, somewhere, somehow, possibly before the galaxy itself was formed. Biological cells (a minute fraction remaining viable would suffice) are included in the dust clouds that form protoplanetary nebulae (PPNe) and planetary systems, such as our own Solar System. Comets, when they condense from interstellar material in the outer regions of a planetary system, incorporate a fraction of viable bacteria. These then multiply exponentially in radioactively heated liquid cometary interiors on timescales of less than a million years. As the comets subsequently re-freeze, the vastly amplified population of bacterial cells remain in a deep frozen state until they are shed in cometary dust tails back into interstellar space – the long-term reservoir of cosmic biology. The cycle of Fig. 1 implies a strong positive feedback with a continuous replacement and amplification of viable bacterial cells in the interstellar medium.

It should be noted that the lower half of the circuit of Fig. 1 could include other delivery modes besides comets contributing to a positive feedback. Life-carrying planetary debris that is expelled from one planetary system can become incorporated in new planetary systems elsewhere, thus providing a process of lateral gene transfers and Darwinian evolution on a cosmic scale …

[later] When a bacterial cell emerges from a sublimating or outgassing comet into the vacuum of interstellar space, free water in its interior (which makes up 60% by weight) is expelled. Cavities develop, leading to a hollow organic grain possessing an average optical refractive index n=1.167. … This property turns out to be of crucial importance in providing an exceedingly close match to the observed scattering behaviour of interstellar dust.

[later] Over a 2–4 mm waveband a prediction of desiccated bacterial dust was verified by subsequent telescope observations in 1981 for the galactic centre infrared source GC-IRS7 (Allen & Wickramasinghe 1981). The remarkable fit displayed in Fig. 3 [see below] implies that some 30% of all the carbon in interstellar space is tied up in the form of carbonaceous dust whose spectra cannot be distinguished from desiccated bacteria.

Infrared signature of bacteria in the Galaxy? Wickramasinghe's Fig. 3. “The first detailed observations of the Galactic centre infrared source GC-IRS7 (Allen & Wickramasinghe 1981) compared with earlier laboratory spectral data for dehydrated bacteria.” See ref. 2010.

[later] If Occam’s razor is to be used to sift competing hypotheses it should be used to discard the increasingly convoluted set of arguments being used to prop up a geocentric model of life. It was once thought that we would never know what stars are made of, but the advent of spectroscopy changed this idea overnight. A mystical ‘ celestial essence of stars ’ was then replaced with common (and not-so-common) chemical elements that were known to be present on Earth. A similar transition from ‘mysterious PAHs’ [see Parts 2 and 3 – NC] and products of a hypothetical interstellar prebiology to biology and biological degradation products on a galaxy-wide scale would seem well overdue. The overwhelming bulk of organic material, including a vast kerogen reservoir and PAHs on our planet, has a biological origin. There is no compelling logic to confine the terrestrial biosphere to Earth. In the absence of evidence that a transformation of inorganic material to life is taking place everywhere, panspermia and a galaxy-wide biosphere would be the simplest hypothesis consistent with all the facts.

[Wickramasinghe’s concluding remarks] It is in the author’s view a mistaken remit of modern astrobiology to seek an origin of life everywhere where conditions appear to be congenial. The genetic components of life, no matter where it first arose, are mixed on a Galaxywide scale. Life was most likely to have been first introduced to Earth during the Hadean epoch by impacting comets billions of years ago, thereby establishing our cosmic ancestry. However, the precise manner by which non-living matter in the cosmos turned into life in the first instance may be a problem that eludes us for generations to come.

Finally, from  that paper, I quote Wickramasinghe’s abstract in full, for the philosophy it expresses.

Abstract: With steadily mounting evidence that points to a cosmic origin of terrestrial life, a cultural barrier prevails against admitting that such a connection exists. Astronomy continues to reveal the presence of organic molecules and organic dust on a huge cosmic scale, amounting to a third of interstellar carbon tied up in this form. Just as the overwhelming bulk of organics on Earth stored over geological timescales are derived from the degradation of living cells, so it seems likely that interstellar organics in large measure also derive from biology. As we enter a new decade – the year 2010 – a clear pronouncement of our likely alien ancestry and of the existence of extraterrestrial life on a cosmic scale would seem to be overdue.

My personal conclusions, to update Comets and Magic Universe, are:

  • The early attempt to link disease epidemics to comets was probably a blunder. It put off or distracted many of Hoyle & Wickramasinghe’s fellow scientists from what was otherwise a remarkable anticipation of the growing evidence for complex carbonaceous materials pervading cosmic space.
  • Wickramasinghe, like Kissel & Krueger [see Part 3], says that life on Earth was started by comets, but his mechanism is the rehydration of pre-existing bacteria instead of creative chemistry in the Earth’s water.
  • The present state of knowledge leaves the hypothesis difficult to confirm or falsify. So it remains on the table, and personally I judge it, with no disparagement intended, to be the second best working hypothesis for the origin of life on Earth, after Kissel & Krueger’s.

And I share Wickramasinghe’s concern about the “cultural barrier”. Science became over-specialized in the creation of university departments in the 19th Century. Since then, in several major advances, earth scientists and biologists put up strong and prolonged resistance when astronomers or astronomically-minded folk suggested:

  • extinctions due to impacting comets and asteroids have redirected the course of evolution (Halley, about a comet)
  • the Earth’s wobbly orbit around the Sun explains the timing of coolings and warmings in the ice ages (Milankovitch)
  • to explain the origin of life on Earth we have to consider possible cosmic sources (Arrhenius)
  • to understand climate change we have to look to the role of cosmic rays in cloud formation (Svensmark)

Plus ça change, plus c’est la même chose.


N. Calder, Comets: Speculation and Discovery (re-issue of The Comet is Coming! BBC Publications 1980) Dover Classics, Dover Publications, New York. 1994

F. Hoyle and C. Wickramasinghe, Diseases from Space, Dent, London, 1979

J. Gadbury, De Cometis, 1665, in the Royal Astronomical Society library.

C. Wickramasinghe, A Journey with Fred Hoyle, World Scientific and Imperial College London Press, 2004

C. Wickramasinghe, “The astrobiological case for our cosmic ancestry”, International Journal of Astrobiology, Vol.9, pp. 119-129, April 2010. The full text is available as a pdf from

This paper (above) refers to a 1982 review by Hoyle and Wickramasinghe. It too is downloadable, but beware – it’s a large document running to 162 pages.…pdf

See also Chandra’s website


3 Responses to Comets and life 4

  1. […] Comets and life 4 […]

  2. […]   两位作者以这种方式作出彗星是动力在地球上生命的历史,并试图解除他们的医疗评论家问tetchily如何从地底的病毒新来的空间知道如何攻击……彗星,当他们浓缩从星际物质在外侧区域的一个行星系统,将一小部分可行的细菌。         原来贴在这里。   彗星和生命的《Calder& 4 # 8226;更新View original post here:Comets and life 4 « Calder's Updates […]

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