From mid-November to early-December of this year Sri Lanka witnessed a rare conjunction of natural phenomena, all pointing to the skies. Frequent sightings of meteors (probably the Leonids) were followed by numerous reports of fireballs, some of which actually resulted in the recovery of carbonaceous meteorites. Interest in all these events was heightened due to several episodes of red rain that fell in the same general timeframe and in the same locations. The red rain phenomenon of Sri Lanka was strikingly similar to the red rain of Kerala that was featured in a cover story in New Scientist of 4 March 2006.
Preliminary examination of the Sri Lankan red rain has shown the presence of red cells almost identical to the Kerala red rain cells. However, despite several years of study by various groups, the Kerala red rain cells have not yet been convincingly identified, and an extraterrestrial origin of the cells still remains a possibility. In the case of the Sri Lankan red rain cells, the mystery deepens with chemical analysis that shows them to contain unusually high concentrations of the elements arsenic and silver. The arsenic abundance is, however, less than a per cent of what would be required if phosphate groups in DNA are to be replaced by arsenate groups, as was recently suggested in studies of the bacterium strain GFAJ-1 of the Halomonadaceae (Science 332, 1163,2011), isolated from Mono Lake, California.
Optical microscope field of red rain cells
It would be tempting to connect the meteors and fireballs with the red rain events experienced in Sri Lanka during November and December 2012. Meteor showers (e.g. the Leonids) occur at regular times in the year whenever the Earth in its orbit crosses the trails of debris from short-period comets. Whilst centimetre-sized particles entering the atmosphere at high speeds burn-up as meteors or shooting stars, larger cometary fragments, containing dust and in some cases living cells, could disperse their particulate content non-destructively into the atmosphere. Many years ago E.G. Bowen (Nature 117, 1121, 1956) discovered a connection between freezing nuclei in tropospheric rain clouds and the incidence of extraterrestrial particles from meteor streams. It was found that as dust from cometary streams (which may possibly include red rain cells) is introduced into the troposphere, heavy rain follows some 30 days later. Larger cometary bolides in a meteor stream that do not disintegrate could end up as fireballs and meteorites that fall to the ground.
Dr. Anil Samaranayake
Director, Medical Research Institute, Ministry of Health
Colombo, Sri Lanka
Prof. N. Chandra Wickramasinghe
Director Buckingham Centre for Astrobiology, Buckingham, UK
There have been interviews with Professor Wickramasinghe about the red rain in: