Alien Downpour: The Red Rain of India

by Brian Dunning
September 21, 2010

It was July of 2001 in the Indian state of Kerala, a land of great tropical loveliness. It has pristine beaches on the Arabian Sea, lush green valleys sloping into its hills, and everywhere are rivers, waterways, and jungle. Kerala is a land of perpetual green beauty, a true garden of Eden. And so how incongruous it was when the rains came, and rather than their normal deluge of clean, clear water, they came down blood red. For two full months through the end of summer, every time it rained, the land was drenched crimson. To this day, some believe it was an invasion of biological material from an alien world.

Superstition runs pretty deep in India, and it's hardly surprising that residents came up with all sorts of ideas about the cause. The rain was frequently described as blood, some taking it as a omen, others as a curse. Some feared it was a sign of Kaliyuga, an age in Hindu tradition characterized by wickedness, greed, and oppression. Many took it as portending the end of the world, and there was genuine fear. One supposedly scientific explanation suggested that a meteor must have struck a flight of bats in mid-air, atomizing them into a cloud of blood which then rained down.

But very quickly, meteorologists filled in the blanks with real science. Red rain had happened before, not just here but in other surrounding countries as well. Researchers noted similar red rainfalls in 1818, 1846, 1872, 1880, 1896, and 1950, including one described by Charles Darwin. Chemical analysis showed that the red rainwater contained carbon, silicon, calcium and magnesium. This gave scientists a clue, and they looked westward. A great cloud of dust, kicked up by high winds over the Rub' al Khali desert in Saudi Arabia, had been carried east across the Arabian Sea. The dust particles seeded great rainstorms above Kerala's steaming jungles, and thus the rain came down tinted red, and full of desert minerals. The Times of India reported that space scientists at the Vikram Sarabhai Space Centre had made this determination using satellite photography, and their findings were published two years later in 2003 in the peer-reviewed Indian Journal of Radio and Space Physics. Thus was the mystery solved to the satisfaction of most scientists.

Correction: Though it's popularly reported, Darwin never actually wrote any reports of "red rain" per se. See this corrections episode to get the full story. —BD

But not to everyone's satisfaction. A few fringe researchers took a second, closer look, and they found something very different. Chief among these was Godfrey Louis and Santhosh Kumar, two physicists who were, at the time of the 2001 rainfall, at Mahatma Gandhi University in Kerala. They noted the same chemical breakdown as the others, but also discovered something else when they examined the red particles microscopically. They weren't just pieces of dust; they appeared to be living, biological cells. How and why could red cells fall from the sky?

Perhaps the cells themselves offered a clue. Louis and Kumar's most extraordinary discovery came when they used dye to stain the cells, to make it easier to study their interiors. They found that the cells had no nuclei, and no genetic material like DNA. This was an astounding revelation. Living cells with no genetic material? The red rain of Kerala didn't look like anything that could have come from Earth's own biosphere. It was, quite simply, life, but not life as we know it.

Louis and Kumar dug, and found a number of people who had reported a loud bang, distinct from thunder, at about 5:30 in the morning on July 25, about three hours before the first red rainfall. They concluded that this was the sonic boom of a comet that entered the atmosphere above Kerala and exploded, distributing its contents throughout the sky. By examining the patterns of the rainfall reports, Louis and Kumar calculated that their hypothetical comet had left an elliptical debris field 450 km by 150 km, consisting of fine red particles that then drifted down into the rain clouds.

Panspermia is what we call organic material moving from one world to another, usually through comet or meteor action. In fact, this is one of the theories for how life may have originated on Earth. In 2010 Louis contributed to a paper claiming that the red cells could have come from the Red Rectangle nebula, or another similar nebula, due to the close match in color between the Kerala cells' fluorescence behavior and the extended red emission from the Red Rectangle.

Louis and Kumar made their first publication of their finding on a website in 2003, and have presented papers at conferences and in astrophysics magazines a number of times since. And every time, they've been the darling of the mass media, with major news agencies like CNN repeating their sensational panspermia story without critique. It's been trumpeted throughout nearly every consumer news publication, although curiously, almost nobody else in the scientific community (and certainly nobody from botanical circles) accepts Louis and Kumar's space spore explanation. This is of little consequence to the news agencies, but to anyone interested in learning about the red rain phenomenon, it should raise the question of other possible causes.

And it turns out that the red rain did have another possible cause, one that was determined quickly and quietly, without fanfare, within a week or two of the first rainfall. It was apparently so mundane that almost nobody paid attention, and even today, you have to dig past reams of panspermia reports to find it.

Very soon after the 2001 rainfall, Kerala's Centre for Earth Science Studies (CESS), which normally studies natural sciences of local importance such as water resource management, had taken a sample of the red rainwater and examined it microscopically. They immediately noticed that the particles appeared to be spores, and so they sent the sample to the government's Tropical Botanical Garden and Research Institute for identification. The spores were incubated and grown, then re-examined, and found to be those of an unremarkable, and extremely common, local algae called Trentepohlia. Trentepohlia is heavy with red-orange carotenoid pigments, so this identification came as no surprise.

Kerala's climate makes it perfect for lichen. Upon just about every tree and long-exposed surface in the region can be found at least some trace of lichen. Lichen is not a species of plant, it is in fact a symbiosis of algae and fungus. Much of Kerala's lichen is red-orange, getting its color from the Trentepohlia algae.

There was only one question not clearly answered, and that was what had caused such a huge population explosion of spores, enough to visibly color the rainwater. It is typical and expected for spores to be found in the atmosphere — we call them stratospheric spores — it was just an unusually large bloom of them. But it's important to remember that every bloom of algae is a different size, and the largest are going to be, by definition, unusually large. There had been plenty of rain that year and conditions were good. That some blooms are larger than others is the way nature works, it's not evidence that something unseen or unknown must have been afoot. The red rain has even happened several times since the famous 2001 fall, and the botanists have found the same Trentepohlia spores every time.

As there was nothing inconclusive or ambiguous about the Institute's identification of the spores, it's not clear why Louis and Kumar later embarked on their own project to come up with their own identification of them, particularly since they were physicists and were completely outside of their specialty. Perhaps they simply hadn't heard the results, though it seems hard to believe that someone wouldn't have brought them to their attention. What is clear is that there was a significant difference between what Louis and Kumar saw when they looked at the spores, and what the botanists saw; and that's the presence of DNA. The botanists found it, Louis and Kumar did not; and as a result, they decided the spores must have been alien.

Searching for genetic material in algae spores is hard. It's much more difficult than with some other types of cells, in part because spores are impermeable to the dyes used to make the material stand out. Spores have extremely durable membranes, designed to protect them from harsh conditions. This makes them incredibly hardy, surviving extreme temperatures, physical abuse, dessication, chemical disinfectants, and even radiation. This is why the botanists at the Tropical Botanical Garden and Research Institute grew the spores in a culture before trying to examine them. If you can get them to germinate, you break that sturdy cell wall from within. It's then much easier to dye them, and the genetic material is then relatively simple to detect. Not being botanists, Louis and Kumar tried dying the spores without growing them; and as might be expected, the cell membranes remained intact and they saw no genetic material.

And so, to summarize the background of the finding that Kerala's red rain consisted of alien cells, we have a completely hypothetical supposition put forth to explain bad data resulting from a methodological error by scientists working outside their discipline. There never was any uncertainty about the algae among Indian botanists, there was only a week or two after the rainfall until what they suspected was confirmed; and yet, it's nearly impossible to find this true cause of the red rain in pop culture. Even today, the overwhelming majority of articles written about Kerala's red rain promote the extraterrestrial alien spore theory. Documentary films are still being made today that make no mention of the algae, but publicize only the sensational alien theory. News articles continue to parrot the misconception that the cells contain no DNA, continuing to quote only Godfrey Louis and the two or three other non-botanists whom he has managed to convince of his alien theory.

All too often, we give undue credence to incredible stories simply because they've been written up in a magazine or broadcast on the news. The red rain of India is one powerful example of the need to provide extraordinary evidence to support an extraordinary claim, and it fails that test. The story of the Trentepohlia spores may not be sexy, and it may not blow anyone's mind, but it's what happened. Stick with the explanations that fit into our understanding of the world, and with the consensus of the majority of specialists, and you'll be right far more often than you'll be wrong.

By Brian Dunning
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