At http://blogs.esa.int/rosetta/2014/11/07/virtis-detects-water-and-carbon-… … as the data is being processed and we may have to wait a while for sound evidence it is worth going back on what was being said as Rosetta approached the comet in November (prior to the Philae lander getting everyone excited). The comment thread appears to have been usurped by EU enthusiasts – and you can keep up to date with the subject of what the comet is composed of at Thunderbolts forum. It seems that prior to the lander bumping up and down on the surface of the comet water and carbon dioxide were detected in the coma. The average temperature was also being monitored and it seems to be around -70 degrees Celsius at the surface and from 100 degrees C to 183 degrees C above the surface. This is due to gases accelerating away from the surface and expanding in the coma leading to a form of cooling known as 'adiabatic expansion'.
This low temperature in the proximity of the comet (and the coma) is interesting when we look at folk lore. In the Irish tale of Cuchulainn, the contorted hero (a comet like object), brought forth megaloads of snow and ice upon Ireland, as the object approached and passed by the Earth.
Other gases detected include carbon monoxide, methanol. methane, formaldehyde, as well as hydrocarbons such as acetylene and ethane.
Elsewhere on the Rosetta blog we learn that there is plenty of water vapour being emitted from the comet coma. The amount varies as the comet rotates but at maximum is some 5 litres a second – but the average is 1 litre a second (or less). However, at http://phys.org/print337503703.html … we are told the water vapour from the comet is significantly different to that found on the Earth. This means the origin of the Earth's oceans may not lie in comets (or dirty snowballs). Is this a prelude to a change in theory, dumping the dirty snowball in favour of a more rocky kind of comet? In any case they may have to review the idea that Earth lost all its water when the planet accreted at the beginning of the solar system formation and in that case they would have to think in terms of water (or its molecules) preserved in the innards of the Earth or on its surface.