Zoo Station

A couple of days back, I had promised Kuldeep and others that I would post excerpts from the New Scientist cover story since it was behind a subscription wall. I haven't been able to do so, since I have been on the road. In my mind, irrespective of whether or not the Kerala red rain/bacteria story is true, the New Scientist story remains one of the most fascinating science stories I have read in recent times. Since most of you already know the details, I'll jump straight to the relevant excerpts.

Louis, a solid-state physicist at Mahatma Gandhi University in Kottayam, was intrigued and decided to study the rain with his student Santhosh Kumar. The pair compiled more than 120 reports of the rain from local newspapers and other sources, and gathered samples of the red rain from spots more than 100 kilometres apart. Under the microscope, they could see red particles 4 to 10 micrometres wide with an average density of about 9 million particles per millilitre. When they dried the samples they found that each cubic metre of rainwater contained about 100 grams of the red stuff. Louis suggests 5 millimetres of red rain would typically have fallen over a square-kilometre area during each of about 100 downpours. That would make 500,000 cubic metres of water in total, containing a staggering 50 tonnes of red particles. What could they be? One possibility was that fine red sand had blown over Kerala from some distant desert. Sand can travel amazingly far.
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But under the microscope, the red particles that rained on Kerala were clearly not sand. Electron micrographs show that they are shaped like biological cells. "They don't look anything like sand, they look biological," says Monica Grady, a meteorite expert at the UK's Open University in Milton Keynes. The cells, if that's what they are, are mostly cup-shaped and have a thick wall. One type of analysis shows their chemical make-up is about 50 per cent carbon and 45 per cent oxygen by weight, along with traces of other elements such as sodium and iron. That's consistent with the components of a biological cell, according to Jeffrey Walker, a molecular biologist from the University of Colorado in Boulder. But although many of the cells have some kind of detached inner capsule, there is no visible cell nucleus, and tests for DNA that Louis carried out came back negative.

Louis rules out a distant terrestrial source for the mysterious particles, because the red rain was concentrated over Kerala for two months despite changes in climate and wind patterns. Could the cells instead be local pollen or fungal spores washed off trees and houses by the rain? Louis says no, because red rain was collected in buckets placed in wide-open spaces. Equally, he says, the red particles can't be pollen or spores from the ground that accumulated in the atmosphere, because the rain would then have been red at the start of a shower; often the colour came later.

Instead, he links the coloured rain to a meteor airburst. During the early hours of 25 July 2001, just hours before the first red rain fell, several people in the Kottayam district heard a loud sonic boom that made their houses rattle. Louis has interviewed some of those who heard it, and concluded that it was too loud to have been an ordinary thunderclap. It's possible that an incoming meteor exploded in the atmosphere.
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What other explanations are there? Wainwright likens the red cells to spores from a rust fungus, or possibly pollen or algae. With Wickramasinghe and others, Wainwright has shown in balloon experiments that winds can carry microbes from the ground to high altitudes. Particles the size of those in the red rain could soar several kilometres above the Earth's surface. The dimpled shape could easily have arisen when the cells collapsed in the microscopy process. If that were true, he says, then the only mystery concerns the lack of DNA. "You wouldn 't expect spores, microbes or algae not to have any DNA," he says. The simplest explanation is that Louis's experiments missed it, so Wainwright wants to repeat the tests. If the cells do turn out to contain DNA, then there is no great mystery. "I'd kind of relax if there was DNA there," says Wainwright.

If there is no DNA, Wainwright argues, the cells might be something extraordinary. He speculates, like Louis, that the lack of DNA might point to some kind of exotic life form, although he admits it would be paradoxical for cells without DNA to be classed as "living". Cockell argues that there could be a simpler explCanation - the red particles are actually blood. "They look like red blood cells to me," he says. The size fits just right; red blood cells are normally about 6 to 8 micrometres wide. They are naturally dimpled just like the red rain particles. What's more, mammalian red blood cells contain no DNA because they don't have a cell nucleus.

It's tough to explain, however, how 50 tonnes of mammal blood could have ended up in rain clouds. Cockell takes a wild guess that maybe a meteor explosion massacred a flock of bats, splattering their blood in all directions. India is home to around 100 species of bats, which sometimes fly to altitudes of 3 kilometres or more. "A giant flock of bats is actually a possibility - maybe a meteor airburst occurred during a bat migration," he says. "But one would have to wonder where the bat wings are." Walker agrees that the particles in the red rain look uncannily like red blood cells. He says a simple test for haemoglobin could resolve this quickly. "If they believe they aren't red blood cells, then they need to explain how they 've managed to eliminate that possibility," says Cockell. "I would have thought some more basic biochemical analysis of these cells would be worthwhile, and that should identify it, whatever it is."

"It's a pity that they don't realise this is interesting without all the extraterrestrial hype," Cockell adds. "How might you get blood into rain? I don't think anyone has observed an event where they've seen an animal ripped apart and its blood distributed in clouds. In some ways, that whole process is far more interesting than what Louis is trying to prove." For blood cells to survive would be astonishing: normally they would be destroyed within minutes if kept in rainwater, unless the salinity was the same as inside the blood cell.

And then comes the most extraordinary claim of all.

Someone will have to verify an observation that Louis made which even he finds astonishing: that the cells replicate. In earlier unpublished papers, Louis says he cultured the red rain cells in unconventional nutrients, such as cedar wood oil, and showed that these DNA-devoid microbes divide happily at a temperature of 300 °C. Louis admits he left these claims out of his latest paper because he thought they would be considered "too extraordinary".

I'll justify the amount of space on this blog devoted to this story using a quote from the story.

Extraordinary is an understatement: if the cells really do replicate we'll have found the first evidence of extraterrestrial life. In the end, though, I didn't find any scientist willing to bet that the red rain of Kerala contained aliens. But everyone agreed it's a cracking good story that's crying out for a proper explanation. "I think you've got to be intrigued," said Wainwright. "If you're not intrigued, then what are you doing in science?"

And I am not even IN science.