Did aliens rain over Kerala in July 2002?

Still, Louis’s theory that ‘‘life forms hitched a ride on a comet’’ is now the subject of a surprising scientific debate. Speaking to The Indian Express from Kottayam, Louis said: ‘‘The rain was biological cells released by a comet shower over Kottayam.’’

The international scientific community agrees that what fell was biological—the cell structure is unmistakable but there is no consensus on where it came from.

On July 25, 2001, the first spell of red rain fell in Kottayam district of Kerala. Over the following two months, it fell sporadically over neighbouring districts. Its average span was 20 minutes and the red was like the colour of blood.

Louis, a solid-state physicist at Mahatma Gandhi University in Kottayam, and his student Santhosh Kumar gathered red rain samples from spots more than 100 km apart. They studied dried particles under the microscope and estimated that the total volume of the red particles was 50 tonnes.

Louis suggests that the meteor was a fragment of a comet carrying microbes from space. The meteor burst shedding these alien microbes in the upper atmosphere. Some of the red microbes mixed with rain clouds and fell immediately, while the rest settled into clouds and fell in rain over the following weeks.

Initial theories had suggested that the red carried dust blown in from the Arabian desert to Kerala. ‘‘The red rain was concentrated over Kerala for two months despite changes in climate and wind patterns,’’ said Louis.

His meteor theory is supported by another event: hours before the first red rain fell, several people in Changanasseri heard a loud boom. This is when, Louis says, the meteor exploded in the atmosphere.

After his pre-press paper was made available to scientists, there have been a range of reactions. ‘‘If they’re not living cells, I don’t know what they are,’’ said Milton Wainwright, a microbiologist at the University of Sheffield, UK quoted in New Scientist. ‘‘Maybe this is the beginning of something amazing.’’

A point that goes in favour of sceptics is the fact that these ‘‘biological forms’’ do not have DNA and there cannot be a living cell without a DNA. Some scientists have proposed a theory that it’s blood from bats or pollen from trees.

However, there is no mistaking that these 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.

Louis sees a link to the ‘‘panspermia’’ theory—that life on Earth evolved from microbes that fell to its surface on a comet. The jury is still out on this one. That’s why Louis sent samples to a lab in Cardiff last month to scientists who came up with the panspermia theory. They are examining the samples. Until the test results come, the aliens haven’t quite landed.