Two planetary scientists from the UK – Prof Chandra Wickramasinghe of the Buckingham Center for Astrobiology and Dr Max Wallis of the University of Cardiff – have a possible explanation for the odd properties of Rosetta’s target comet: micro-organisms that shape cometary activity.
This false-color four-image mosaic comprises images taken from a distance of 28.7 km from the center of Comet 67P/Churyumov-Gerasimenko on 3 February 2015. The mosaic measures 4.2 x 4.6 km. Image credit: ESA / Rosetta / NAVCAM / CC BY-SA IGO 3.0.
Comet 67P/Churyumov-Gerasimenko is a relatively small Jupiter family comet, about 2.5 miles (4 km) in diameter, moving at a speed as great as 84,000 mph (135,000 km per hour).
It loops around the Sun between the orbits of Jupiter and Earth, that is, between about 500 million and 115.5 million miles (800 million and 186 million km) from the Sun.
“Despite the comet’s very black crust, Rosetta’s remarkable images show several indicators of an underlying icy morphology. The comet displays smooth, planar ‘seas’ and flat-bottomed craters, both features seen also on comet Tempel-1,” the scientists said.
“Comet 67P’s surface is peppered with mega-boulders like comet Hartley-2, while parallel furrowed terrain appears as a new ice feature. The largest ‘sea’ curves around one lobe of the comet, and the crater lakes extending to 490 feet (150 m) across are re-frozen bodies of water overlain with organic-rich debris of order 3.9 inches (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.”
“These features are all consistent with a mixture of ice and organic material that consolidate under the Sun’s warming during the comet’s orbiting in space, when active micro-organisms can be supported,” Dr Wallis and Prof Wickramasinghe said.
In their model, alien microorganisms probably require liquid water bodies to colonize the comet and could inhabit cracks in its ice and ‘snow.’
Organisms containing anti-freeze salts are particularly good at adapting to these conditions and some could be active at temperatures as low as minus 40 degrees Fahrenheit (minus 40 degrees Celsius).
Sunlit areas of Rosetta’s comet have approached this temperature in September 2014, when at 310 million miles (500 million km) from the Sun and weak gas emissions were evident. As it travels to its closest point to the Sun – perihelion at 121 million miles (195 million km) – the temperature is rising, gassing increasing and the micro-organisms should become increasingly active.
“Outgassing was already evident in September at 3.3 AU, with surface temperature peaks of 220-230 K, which implies loosely bound H2O and/or unconsolidated organic mixtures. Increasing rates of gassing as Rosetta follows comet 67P around its 1.3 AU perihelion will hopefully reveal the activation of possible microorganisms as well as the nature and prevalence of near-surface ices,” the scientists said.
“Rosetta 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,” Dr Wallis said.
“If the Rosetta orbiter has found evidence of life on the comet, it would be a fitting tribute to mark the centenary of the birth of Sir Fred Hoyle, one of the undisputable pioneers of astrobiology,” Prof Wickramasinghe added.
The scientists presented their idea today at the National Astronomy Meeting in Llandudno, Wales, UK.
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Max K. Wallis & Chandra Wickramasinghe. Icy structures and terrain in comet 67P. NAM 2015: National Astronomy Meeting, Llandudno, Wales
