On 29 December 2012, a fireball lit up the early evening skies over the Sri Lankan province of Polonnaruwa. Hot, sparkling fragments of the fireball rained down across the countryside and witnesses reported the strong odour of tar or asphalt.
The general properties of these three stones immediately mark them out as unusual. One stone, for example, had a density of less than 1 gram per cubic centimetre, less than all known carbonaceous meteorites. It had a partially fused crust, good evidence of atmospheric heating, a carbon content of up to 4 per cent and contained an abundance of organic compounds with a high molecular weight, which is not unknown in meteorites. On this evidence, Wallis and co think the fireball was probably a small comet.
The most startling claims, however, are based on electron microscope images of structures within the stones (see above). Wallis and co. say that one image shows a complex, thick-walled, carbon-rich microfossil about 100 micrometres across that bares similarities with a group of largely extinct marine dinoflagellate algae.
They say another image shows well-preserved flagella that are 2 micrometres in diameter and 100 micrometres long. By terrestrial standards, that’s extremely long and thin, which Wallis and co. interpret as evidence of formation in a low-gravity, low-pressure environment.
If the paper is taken at face value, one obvious question that arises is where these samples came from. Wallis and c.o have their own ideas: “The presence of fossilized biological structures provides compelling evidence in support of the theory of cometary panspermia first proposed over thirty years ago,” they say.
This is an idea put forward by Fred Hoyle and Chandra Wickramasinghe, the latter being a member of the team who has carried out this analysis.
Astrobiologists Find Ancient Fossils in Fireball Fragments | MIT Technology Review