Microbes on a comet?! Why scientists are skeptical
Sen鈥擳wo astronomers made the controversial claim today to have detected potential evidence for life on the comet being studied by Europe鈥檚 Rosetta space probe. But their report was immediately met with general skepticism.
Dr Max Wallis, of Cardiff University, says Comet 67P/Churyumov-Gerasimenko could be a more friendly environment for simple organisms than the Arctic and Antarctic on Earth where hardy microbes have been found.
Dr Wallis, and colleague Professor Chandra Wickramasinghe, Director of the Buckingham Centre for Astrobiology, say that features on the comet鈥檚 surface appear to have been shaped by micro-organisms. Dr Wallis explained their study at the National Astronomy Meeting (NAM) at Llandudno, Wales.
They say their radical explanation is supported by images from orbiter Rosetta and data collected by its little lander Philae. However, the extraordinary claims have been met with ridicule by mainstream scientists, many of whom are surprised it made it onto the science programme of this major conference, organised by the Royal Astronomical Society.
Images of Comet 67P鈥檚 twin-lobed structure shows a black crust covering ice, and large smooth plains, flat-bottomed craters and with huge boulders littering the surface. The crater floors are said to be areas of water that has refrozen and is covered with organic debris. Grooves have been produced where the nucleus has cracked under the strains of constant flexing.
Dr Wallis and Professor Wickramasinghe believe these features can be explained by the regular warming of the comet, and its effect on a mix of ice and organic material, during its elliptical orbit of the Sun. They say this warming can support the existence of active micro-organisms which could inhabit cracks in the comet鈥檚 ice and snow. Organisms containing anti-freeze salts would remain active in temperatures as low as -40掳, they say.
Further evidence for comet life, according to the pair, is Philae鈥檚 detection of an abundant amount of complex organic molecules on 67P鈥檚 surface and in infrared images taken by Rosetta鈥檚 cameras. Dr Wallis said in a statement: 鈥淩osetta has already shown that the comet is not to be seen as a deep-frozen inactive body, but supports geological processes and could be more hospitable to micro-life than our Arctic and Antarctic regions.鈥�
The start of the abstract, or summary, of the presentation reads: 鈥淒espite the comet鈥檚 very black crust, Rosetta鈥檚 remarkable images show several indicators of an underlying icy morphology. Comet 67P displays smooth, planar 鈥榮eas鈥� (the largest 600mx 800m) and flat-bottomed craters, both features seen also on comet Tempel-1. Comet 67P鈥檚 surface is peppered with mega-boulders (10-70km) like comet Hartley-2, while parallel furrowed terrain appears as a new ice feature.
鈥淭he largest sea (Cheops Sea, 600 x 800m) curves around one lobe of the 4km diameter comet, and the crater lakes extending to ~150m across are re-frozen bodies of water overlain with organic-rich debris (sublimation lag) of order 10 cm. The parallel furrows relate to flexing of the asymmetric and spinning two-lobe body, which generates fractures in an underlying body of ice. The mega-boulders are hypothesised to arise from bolide impacts into ice.鈥�
It adds: 鈥淚ncreasing rates of gassing as Rosetta follows comet 67P around its 1.3 AU perihelion will hopefully reveal the activation of possible micro-organisms as well as the nature and prevalence of near-surface ices.鈥�
The comet session at NAM was run by Dr Colin Snodgrass, of the UK鈥檚 Open University at Milton Keynes. He defended the contribution on Twitter, saying: 鈥淎s the session chair, it is there as the abstract is perfectly reasonable. We don鈥檛 control PR though.鈥�
Rosetta chief scientist Matt Taylor tweeted the reply: 鈥淚ndeed, we should allow things to be put up there for discussion.鈥�
Another leading comet scientist, Professor Alan Fitzsimmons, of Queens University, Belfast, tweeted that organisers should not stifle ideas. But he believes the research is flawed. He told Sen: 鈥淪cientists are rightly fascinated by the search for life elsewhere, and the possibility of the delivery of life to Earth from elsewhere remains an intriguing line of enquiry. However all measurements from Rosetta or by Earth-based telescopes on comets can be explained by much simpler chemical and physical processes than involving extra-trerrestrial life.
鈥淭hese scientists seem to have forgotten Carl Sagan鈥檚 maxim that 鈥榚xtraordinary claims require extraordinary evidence鈥�. They don鈥檛 have it.鈥�
Sen was at Dr Wallis鈥檚 presentation. He got a polite reception from his fellow scientists as he talked of 鈥減otential biofossils鈥� and 鈥減otential biomarkers鈥�, concluding 鈥渋f there is any active biology in the comet, we鈥檇 hope to detect it.鈥� But one comet expert pointedly commented that there would be other theories.
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