Thursday, 9 July 2015

Do micro-organisms explain features on comets?

So was the RAS’s provocative headline on the Press Release for our presentation on 6th July Icy structures and terrain in comet 67P.
    The thrust of the talk was that the comet appears more habitable for microorganisms than the Arctic and Antarctic regions, with its organic-rich surface warming in sunlight, shielding an icy environment below a protective crust which traps gases.  A second point linked the surface crust with particles from comets collected in the stratosphere.  These comprise consolidated aggregates as well as ‘fluffy’ smoke-like particles, both high in carbon.  The former could be identified with fragments of the surface crust - some of these studied in Cardiff University labs show embedded Si-rich fibres, unlike crystalline astrophysical silicates.  The fibres were suggested to be spines from terrestrial  ice diatoms (Miyake, EPSC 2013).

What of the refutation no-alien-life-on-philae-comet ? Stuart Clark ignored the substance, approving instead of Uwe Meierhenrich (co-investigator on Philae’s COSAC chemical analyser) telling him a comet’s black surface crust was a prediction made in 1986 by J. Mayo Greenberg (Nature 321, 385), who had modelled what would happen to naturally occurring organic molecules on the comet when they were struck by cosmic rays and light. “These explanations seem to be valid, also with regard to new data of the cometary Rosetta mission,” wrote Meierhenrich, though the chemistry is indecisive.

Hoyle & Wickramasinghe did publish the prediction of a black surface (Earth Moon Planets 36, 289) before Greenberg in 1986.  Significantly, the Vega/Giotto missions to comet Halley proved Greenberg’s "bird’s nest" structure of rod-particles and UV-processed condensates on mineral cores to be wrong. The PIA and PUMA dust analysers found carbonaceous (CHON) particles, mineral particles and mixed ones.  The carbonaceous CHON component is highly complex, more than the UV-induced compounds of Greenberg’s experiments.  
   Cometary science needs to include past discoveries over comet Halley as well as newer ones on interplanetary dust particles.

Relevant papers in the RAS session Comets: Rosetta results and related science
Cometary dust properties measured by Rosetta GIADA:   Simon F. Green (OU) + GIADA Science Team.  GIADA has detected two distinct particle populations emitted from the nucleus: compact, 0.03-1 mm grains analogous to the processed mineral grains detected by Stardust, and ultra-low density fluffy aggregates of sub-micron grains with diameters 0.2-2.5 mm.

Comet nucleus surface properties in-situ, in the lab and on the computer: Axel Hagermann, DPS, The Open University

The picture of the physical nature of cometary nuclei has been changing dramatically since Giotto's encounter with 1P/Halley. The talk used information from laboratory experiments, computer models and in-situ measurements. The comet is rugged with firm surface and dark surface crust.  How is this compatible with low density?  Philae’s drill failed to penetrate when on low power (before shut down).  The OU group have repeated laboratory simulation of building up a dust-crust from a snow-dirt mix, as in the COSI experiments in the ’90s (Gruen et al).  Heat transport via vapour convection dominates over thermal convection when T>205K.  Fluffy snow converts to hard but porous ice under vapour transport, as modelled by Kossacki (Icarus 2015, applied to comet Tempel-1).  Thus, sintering of the snow-dirt mix increases the contact between ice grains with no change in porosity, so creating the firm and coherent surface crust. But the model contains mineral particles only, not the carbonaceous component which chemically degrades near the surface.

Wednesday, 8 July 2015

Storm over Life-on-Comets concept

TV - ITN report, Monday 6th July:  There could be life beneath the surface of the comet 67P/Churyumov-Gerasimenko according to two UK astronomers. Apparently the comet displays characteristics typical of an environment that could support alien life, including a black crust and icy lakes. Rosetta, the European Space Agency [ESA], spacecraft is also said to have picked up clusters of organic material that resemble viral particles.
  
## And two articles in The Guardian
  Neither Rosetta nor Philae are equipped to search for direct evidence of life after a proposal to include this in the mission was allegedly laughed out of court.

## Then the bloggers got busy:
"This morning, several news outlets gave voice to an extraordinary claim... But extraordinary claims, we all know, require extraordinary evidence. So guess what these morning’s claims were lacking!"

## Storm over the Concept, not the Content
What the paper at the RAS meeting concluded from considering various indications of ice below the dark crust is that the comet would be more hospitable to microorganisms (terrestrial, not 'alien' ones) than the Arctic and Antarctic; I added to this previously-published stratospheric microdust particles which can now be identified with fragments of such a comet’s crust. Surely rather mild claims! 
   The critics attack Press Reports of the RAS press release in their popular, exaggerated language, rather than consider the RAS Abstract and published work linked to it (previous post).  Why such a reaction from people who call themselves scientists, who should be concerned with the concept and evidence, even if poorly presented?  Why do critics use debating strategies and extravagant language, quite non-scientifically ?
  •    The hoary old saying about extraordinary claims requiring extraordinary evidence is repeated, yet the evidence comprises some ignored as not fitting mainstream theories and some from samples studied in Cardiff University labs.  The evidence is extraordinary only in the way it’s put together.  No-one was concerned about stratospheric dust containing siliceous fibres until identified as extraterrestrial with silicious spines of diatoms embedded in the matrix.  No-one was really concerned until the tentative identification of microdust particles as bits of cometary crust such as found on comet CG.
  •    No surprise that galaxy-astrophysicist Jillian Scudder failed to recognise potentially “extraordinary evidence”.
  •    The ESA project’s Matt Taylor declares “pure speculation”, yet he’s well aware of the published work and well aware that Rosetta studies have confirmed our concept of a cometary crust of carbonaceous-mineral aggregate. He saw our evidence of comet-like particles containing bio-fibres.  Is he bound by ESA’s decision against seeking evidence of extraterrestrial life (first Guardian article) ?
  •    Sarah Hörst says her research horizon is the ‘origin of life on Earth’.  Have discoveries of the hardiness of microorganisms carried on meteorites from Mars and space passed her by?  Perhaps she's unaware of panspermia studies, showing that viable spores (and DNA) can spread between planets and, on some arguments, spread to the interstellar dust that contributes to new planetary systems?
  •    Monika Grady is well aware of this as a meteoriticist, so she comments more moderately: “highly unlikely”. We await her argument  for saying our stratospheric dust particles are unlikely to come from a comet and/or unlikely to be representative of comet CG’s crust.

Why such unscientific reactions?  Life on other planets and planetary systems is largely accepted amongst the public.  Spores travelling within meteorites to nearby comets and planets are known to potentially survive.  Only the scientific establishment declares panspermia is “extraordinary”, sticking to the old life-began-on-Earth paradigm for the various sociological reasons given by Thomas Kuhn (Structure of Scientific Revolutions).    
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