WHEN red rain fell over southern India in 2001 it was sensationally suggested that the red particles in the rain could be alien microbes. Now, after weeks of analysis at two labs in the UK, microbiologists are still struggling to identify them. It sounds like an episode of The X-Files, but a down-to-Earth explanation is looking the more likely outcome.
Astronomer Chandra Wickramasinghe is studying the cells with microbiologists at Cardiff University. 鈥淎s the days pass, I鈥檓 getting more and more convinced that these are exceedingly unusual biological cells,鈥� he says.
The red rain fell sporadically over Kerala during two months in 2001. Godfrey Louis, a physicist at Mahatma Gandhi University in Kottayam in Kerala, examined the red particles and, unable to find DNA, suggested that they might be alien microbes that had fallen to Earth on a comet (New Scientist, 4 March, p 34).
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If so, they would be the best evidence to date of 鈥減anspermia鈥�, the theory that primitive life forms fly around interplanetary space on chunks of rock and ice. However, other scientists who read Louis鈥檚 report thought the red particles could be terrestrial cells that had somehow blown up into the rain clouds. Suggestions included fungal spores, red algae and mammalian red blood cells.
At the end of February, Louis sent samples of the red rain to Wickramasinghe, a champion of the panspermia theory. His team has analysed the samples, as has a second team led by Milton Wainwright, a microbiologist at the University of Sheffield.
Both teams say microscopy confirms that the particles are biological cells. They are not red blood cells because they do not contain haemoglobin. It鈥檚 unlikely that they are fungal spores or red algae. They don鈥檛 contain chitin, a key component of fungal cell walls. Nor do they contain the chloroplasts, the organelles in which photosynthesis takes place, that are typical of red algae.
But they do, after all, contain DNA. A simple DNA stain test in Sheffield came back positive. However, more rigorous tests in Cardiff that try to amplify specific DNA sequences have so far failed. 鈥淭hat doesn鈥檛 mean there鈥檚 no DNA, it means that the DNA is probably unusual,鈥� Wickramasinghe suggests.
The red cells have unusually thick, sturdy walls, and some contain daughter cells that Wainwright says are puzzling. He stresses, though, that the cells could be ordinary, terrestrial organisms he is not familiar with.
鈥淭he particles could be the best evidence yet that primitive life forms fly around interplanetary space on chunks of rock and ice鈥�
Something like the Trentepohlia alga, perhaps? That鈥檚 the conclusion of microbiologists at the Tropical Botanic Garden and Research Institute in Kerala, who say they have cultured the cells and grown Trentepohlia, an alga common in Kottayam, where the first report of the red rain originated. Formal DNA identification awaits.
Both UK teams will continue DNA tests and say they will not release full details of their results until they have been peer reviewed. Sadly for X-Files fans, a terrestrial origin is looking more likely. How the cells fell as rain, that鈥檚 the mystery.
