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It's raining aliens(New Scientist Via Thomson Dialog NewsEdge)I'VE heard plenty of tales about freak weather that are strange, but nonetheless true. In August 2000, a shower of sprats, dead but conveniently still fresh, fell from the skies onto the English port of Great Yarmouth just after a thunderstorm. A torrent of live toads pelted a Mexican town in June 1997. And in 2001, 50 tonnes of alien life forms rained down from the clouds over India. Actually, I'm not sure that the alien story is true. But it is surprisingly persistent. I first saw it in 2003 in a scientific paper written by Godfrey Louis, a physicist working in the Indian state of Kerala, on the country's southern tip. He described how, during two months in 2001, red rain fell sporadically right across the state. No one could explain it, but after lengthy studies of red particles in the rainwater, Louis came to the extraordinary conclusion that they were alien microbes that hitched a ride to Earth on a comet. To most people, that would sound eccentric at the very least. It looked as if the idea would quietly wither on the vine. Then in January this year, it turned out that Louis's theory is still alive and kicking, and soon to roll off the press in a reputable peer-reviewed journal. I sent a preprint to several researchers, who despite voicing mixed opinions almost all agreed about one thing: the red particles Louis describes look biological. "If they're not living cells, I don't know what they are," said Milton Wainwright, a microbiologist at the University of Sheffield, UK. "Maybe this is the beginning of something amazing." Another scientist simply commented: "Sounds like bullshit to me." That was it I could resist this weird and controversial story no longer. The saga dates back to 25 July 2001, when red rain fell in a district of Kerala called Kottayam. Over the following two months, red rain fell sporadically there and in other Kerala districts, gradually tailing off over time. The local newspapers buzzed with eyewitness reports. People found their clothes stained by red raindrops. Although these usually had a mild red tint, sometimes the colour was so strong that witnesses compared it to blood. Usually, the red rain would fall for less than 20 minutes. 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. In July 1968, for instance, fine grit in raindrops left parts of southern England coloured rusty red. The sand had blown from the Sahara inside a massive high-pressure system before falling in a rain shower. 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. Louis then takes a large leap and suggests the meteor was a fragment of a comet harbouring microbes from space. He thinks that is the only explanation for the red rain pattern. The meteor flew over Kerala from north to south, he suggests, shedding fragments and alien microbes in the upper atmosphere, before finally exploding over Kottayam district. There, some of the red microbes mixed with rain clouds and fell fairly quickly, while the rest gradually settled into the clouds and fell in rain over the following weeks. "Yes, it is an extraordinary claim, but I have to report what I observe," says Louis. "We are not able to explain it by assuming a terrestrial object." The red particles look like biological cells, he stresses, but contain no DNA. They could therefore be exotic, alien life forms unknown to science. Far-fetched? Certainly sounds it. But the idea would undoubtedly have appealed to the late University of Cambridge astronomer Fred Hoyle, champion of the "panspermia" theory. With Chandra Wickramasinghe of Cardiff University, UK, Hoyle developed the idea that life on Earth evolved from microbes that fell to its surface on a comet. In this picture, primitive life forms could be ubiquitous throughout the universe, peppered among the planets and the stars. Philosophically, panspermia has a certain appeal. It could resolve the genuine puzzle about why life arose on Earth so fast. The solar system began its life some 4.5 billion years ago as a hostile interplanetary war zone, with rocky missiles pelting everything in sight. Around 3.9 billion years ago, the Earth suffered a particularly violent bombardment that pulverised its crust. Yet carbon isotopes in ancient rocks hint that primitive microbes were thriving just 50,000 years later a blink of an eye in evolutionary terms. Panspermia allows off-the-shelf microbes to arrive on the newly hospitable Earth. This waves away the apparent paradox that the Earth is the only place in the entire cosmos where we've found signs of life. From experience, astronomers assume that if something has occurred once in the universe, it's probably occurred many more times we just haven't seen it yet. Panspermia developed a touch of giggle-factor when Hoyle and Wickramasinghe blamed extraterrestrial viruses for flu epidemics. But it has come back into fashion of late, and proponents argue there's plenty of evidence for it. Experiments have shown that some tough bacteria can survive for years in space, despite the extreme cold and high levels of radiation. Others have proved that some of these bugs could survive the high-speed collisions that they would experience if they slammed into the Earth on a comet. The idea of primitive microbes flying around the solar system in its early days is not as wild as it seems. "Most of the rocks near the surface of the Earth are shot through with microbial life. It would be a fairly simple thing for a little piece of the crust to be ejected and life survive and land somewhere else," says Walker. On balance, he says, he'd bet that life began here on Earth. But he wouldn't be that surprised if evidence emerged that life started somewhere else and was delivered to Earth by a hunk of space rock. Extraordinary claimsIn 1996, Martian meteorite ALH 84001 caused a furore when some scientists claimed that it harboured fossil bugs. The case was never proved. "But the most interesting information that we gathered from that meteorite was that when the rock was ejected from Mars and travelled to the Earth, the temperature of the interior never exceeded something like 50 C," says Walker. "Plenty of microbes can survive that, especially spores." All in all, it seems that panspermia could work. Now Louis thinks the red rain of Kerala provides evidence that it actually does. His new report on the subject, which will appear in Astrophysics and Space Science in the next few months, is impressive in its detail, according to Wainwright. "Everything in the paper is done correctly, there's nothing wacky about it," he says. Grady says it is "very, very thorough indeed". However, if scientists have a favourite quote, it's this one, popularised by Carl Sagan: "extraordinary claims require extraordinary evidence". I'm hearing it a lot in discussions about the red rain of Kerala. Grady thinks Louis and Kumar have jumped to the extraterrestrial conclusion far too quickly. "They seem to prefer the most bizarre explanation they could find," agrees Charles Cockell at the Open University, who studies the microbiology of extreme rocky environments. 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 explanation 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. In the next few weeks, the mystery of Kerala's red rain may finally be solved. Louis sent samples to Wickramasinghe's lab in Cardiff last month. As New Scientist went to press, he and Wainwright were still analysing them. If they can't explain the origin of the samples, then the suggestion that they are alien life will gain credence. In that case, 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". 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?" A preprint of Godfrey Louis's paper can be found at www.arxiv.org/abs/astro-ph/0601022 The results of the latest tests will be published on www.newscientist.com |