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Rain water sample (left) and after the particles settled (right). Dried sediment (center).
Red rain collected in buckets

From July 25 to September 23, 2001, red rain sporadically fell on the southern Indian state of Kerala. Heavy downpours occurred in which the rain was colored red, staining clothes pink.[1] Yellow, green, and black rain was also reported.[2][3][4] Colored rain had been reported in Kerala in as early as 1896 and several times since then.[5]

It was initially thought that the rains were colored by fallout from a hypothetical meteor burst, but a study commissioned by the Government of India found that the rains had been colored by airborne spores from locally prolific terrestrial algae.[5]

It was not until early 2006 that the colored rains of Kerala gained widespread attention when the popular media reported that Godfrey Louis and Santhosh Kumar of the Mahatma Gandhi University in Kottayam proposed a controversial hypothesis that the colored particles were extraterrestrial cells.[3]



Kottayam district in Kerala, which experienced the most intense red rainfall

The colored rain of Kerala began falling on July 25, 2001, in the districts of Kottayam and Idukki in the southern part of the state. Yellow, green, and black rain was also reported.[2][3][4] Many more occurrences of the red rain were reported over the following ten days, and then with diminishing frequency until late September.[3] According to locals, the first colored rain was preceded by a loud thunderclap and flash of light, and followed by groves of trees shedding shriveled grey "burnt" leaves. Shriveled leaves and the disappearance and sudden formation of wells were also reported around the same time in the area.[6][7][8] It typically fell over small areas, no more than a few square kilometers in size, and was sometimes so localized that normal rain could be falling just a few meters away from the red rain. Red rainfalls typically lasted less than 20 minutes.[3] Each milliliter of rain water contained about 9 million red particles, and each liter of rainwater contained approximately 100 milligrams of solids. Extrapolating these figures to the total amount of red rain estimated to have fallen, it was estimated 50,000 kilograms of red particles had fallen on Kerala.[3]

Description of the particles

Photomicrograph of particles from red rain sample
Particles under a scanning electron microscope
A single spore viewed with a transmission electron microscope, purportedly showing a detached inner capsule.

The brownish-red solid separated from the red rain consisted of about 90% round red particles and the balance consisted of debris.[5] The particles in suspension in the rain water were responsible for the color of the rain, which at times was as strongly colored red. A small percentage of particles were white or had light yellow, bluish gray and green tints.[3] The particles were typically 4 to 10 µm across and spherical or oval. Electron microscope images showed the particles as having a depressed center, suggestive of biological cells. At still higher magnification some particles showed internal structures.[3]

Chemical composition

Several groups of researchers analyzed the chemical elements in the solid particles and different techniques gave similar results. The particles were composed mostly of carbon and oxygen with lesser amounts of hydrogen, nitrogen, silicon, chlorine and metals.

The samples of water were brought to the Centre for Earth Science Studies (CESS) in India, where they separated the suspended particles by filtration. The pH (acidity) of the water was found to be around 7 (neutral), which is the pH for normal rain water. The electrical conductivity of the rainwater showed the absence of any dissolved salts. Sediment (red particles plus debris) was collected and analyzed by the CESS using a combination of ion-coupled plasma mass spectrometry, atomic absorption spectrometry and wet chemical methods. The major elements found are listed below.[5] The CESS analysis also showed significant amounts of heavy metals in the raindust, including nickel (43 ppm), manganese (59 ppm), titanium (321 ppm), chromium (67ppm) and copper (55 ppm).

CESS analysis: Major elements present in the dried sediment
Element Al K Mg Ca Na Fe Si C P
Weight % 1.00 0.26 1.48 2.52 0.49 0.61 7.50 51.00 0.08

Louis and Kumar used energy dispersive X-ray spectroscopy analysis of the red solid and showed that the particles were composed of mostly carbon and oxygen, with trace amounts of silicon and iron[3] (see table below).

Elemental composition of red cells by EDXRF analysis
Element Weight % Atomic % Standards
C 49.53 57.83 CaCO3
O 45.42 39.82 Quartz
Na 0.69 0.42 Albite
Al 0.41 0.21 Al2O3
Si 2.85 1.42 Quartz
Cl 0.12 0.05 KCl
Fe 0.97 0.24 Fe

A CHN analyzer showed content of 43.03% carbon, 4.43% hydrogen, and 1.84% nitrogen.[3]

J. Thomas Brenna in the Division of Nutritional Sciences at Cornell University conducted carbon and nitrogen isotope analyses using a scanning electron microscope with X-ray microanalysis, an elemental analyzer, and an isotope ratio (IR) mass spectrometer. The red particles collapsed when dried, which suggested that they were filled with fluid. The amino acids in the particles were analyzed and seven were identified (in order of concentration): phenylalanine, glutamic acid/glutamine, serine, aspartic acid, threonine, and arginine. He concluded that the results were consistent with a marine origin or a terrestrial plant that uses a C4 photosynthetic pathway.[9]

Official report

Initially, the Centre for Earth Science Studies (CESS) stated that the likely cause of the red rain was an exploding meteor, which had dispersed about 1,000 kg (around one ton) of material. A few days later, following a basic light microscopy evaluation, the CESS retracted this as they noticed the particles resembled spores,[10] and because debris from a meteor would not have continued to fall from the stratosphere onto the same area while unaffected by wind. A sample was, therefore, handed over to the Tropical Botanic Garden and Research Institute (TBGRI) for microbiological studies, where the spores were allowed to grow in a medium suitable for growth of algae and fungi. The inoculated petri dishes and conical flasks were incubated for three to seven days and the culture was observed under a microscope.

In November 2001, commissioned by the Government of India's Department of Science & Technology, the Center for Earth Science Studies (CESS) and the Tropical Botanical Garden and Research Institute (TBGRI) issued a joint report which concluded that:[5][10]

The color was found to be due to the presence of a large amount of spores of a lichen-forming alga belonging to the genus Trentepohlia. Field verification showed that the region had plenty of such lichens. Samples of lichen taken from Changanacherry, when cultured in an algal medium, also showed the presence of the same species of algae. Both samples (from rainwater and from trees) produced the same kind of algae, indicating that the spores seen in the rainwater most probably came from local sources.

The site was again visited on August 16, 2001 and it was found that almost all the trees, rocks and even lamp posts in the region were full of Trentepohlia lichen, and estimated that the extent of lichen in the region is sufficient to generate the quantity of spores seen in the rainwater.[5] Although red or orange, Trentepohlia is a Chlorophyte green alga which can grow abundantly on tree bark or damp soil and rocks, but is also the photosynthetic symbiont or photobiont of many lichens, including some of those abundant on the trees in Changanacherry area.[5] The strong orange colour of the algae, which masks the green of the chlorophyll, is caused by the presence of large quantities of orange carotenoid pigments. A lichen is not a single organism, but the result of a partnership (symbiosis) between a fungus and an alga or cyanobacteria.

The report also stated that there was no meteoric, volcanic or desert dust origin present in the rainwater and that its color was not due to any dissolved gases or pollutants.[5] The report concluded that heavy rains in Kerala -in the weeks preceding the red rains- could have caused the widespread growth of lichens, which had given rise to a large quantity of spores into the atmosphere. However, for these lichen to release their spores simultaneously, it is necessary for them to enter their reproductive phase at about the same time. The CESS report noted that while this may be a possibility, it is quite improbable.[5] Also, they could find no satisfactory explanation for the apparently extraordinary dispersal, nor for the apparent uptake of the spores into clouds. CESS scientists noted that "While the cause of the color in the rainfall has been identified, finding the answers to these questions is a challenge."[10]

Parts of the CESS/TBGRI report were supported by Milton Wainwright at Sheffield University, who, together with Chandra Wickramasinghe, has studied stratospheric spores.[1][11] In March 2006 he said the particles were similar in appearance to spores of a rust fungus,[12] later saying that he had confirmed their similarity to spores or algae, and found no evidence to suggest that the rain contained dust, sand, fat globules, or blood.[13]

Alternative hypotheses

History records many instances of unusual objects falling with the rain — in 2000, in an example of raining animals, a small waterspout in the North Sea sucked up a school of fish a mile off shore, depositing them shortly afterwards on Great Yarmouth in the United Kingdom.[14] Colored rain is by no means rare, and can often be explained by the airborne transport of dust from desert or other dry regions which is washed down by rain. "Red Rains" have been frequently described in southern Europe, with increasing reports in recent years.[15][16] One such case occurred in England in 1903, when dust was carried from the Sahara and fell with rain in February of that year.[17]

At first, the red rain in Kerala was attributed to the same effect, with dust from the deserts of Arabia initially the suspect.[6] LIDAR observations had detected a cloud of dust in the atmosphere near Kerala in the days preceding the outbreak of the red rain.[18][19] However, laboratory tests from all involved teams ruled out the particles were desert sand.

K.K. Sasidharan Pillai, a senior scientific assistant in the Indian Meteorological Department, proposed dust and acidic material from an eruption of Mayon Volcano in the Philippines as an explanation for the colored rain and the "burnt" leaves.[20] The volcano was erupting in June and July 2001[21] and Pillai calculated that the Eastern or Equatorial jet stream could have transported volcanic material to Kerala in 25–36 hours. The Equatorial jet stream is unusual in that it flows from east to west at about 10° N,[22] approximately the same latitude as Kerala (8° N) and Mayon Volcano (13° N). This hypothesis was also ruled out as the particles were neither acidic nor of volcanic origin, but were spores.[5]

A study has been published showing a correlation between historic reports of colored rains and of meteors;[23] the author of the paper, Patrick McCafferty, stated that sixty of these events (colored rain), or 36 %, were linked to meteoritic or cometary activity. But not always strongly. Sometimes the fall of red rain seems to have occurred after an airburst, as from a meteor exploding in air; other times the odd rainfall is merely recorded in the same year as the appearance of a comet.


Extraterrestrial hypothesis

In 2003 Godfrey Louis and Santhosh Kumar, physicists at the Mahatma Gandhi University in Kottayam, Kerala, posted an article entitled “Cometary panspermia explains the red rain of Kerala”[24] in the on-line, non-peer reviewed arXiv web site. While the CESS report said there was no apparent relationship between the loud sound (possibly a sonic boom) and flash of light which preceded the red rain, to Louis and Kumar it was a key piece of evidence. They proposed that a meteor (from a comet containing the red particles) caused the sound and flash and when it disintegrated over Kerala it released the red particles which slowly fell to the ground. However, they omitted an explanation on how debris from a meteor continued to fall in the same area over a period of two months while unaffected from winds.

Their work indicated that the particles were of biological origin (consistent with the CESS report), however, they invoked the panspermia hypothesis to explain the presence of cells in a supposed fall of meteoric material.[25][26][27] Additionally, using ethidium bromide they were unable to detect DNA or RNA in the particles. Two months later they posted another paper on the same web site entitled "New biology of red rain extremophiles prove cometary panspermia"[28] in which they reported that

"The microorganism isolated from the red rain of Kerala shows very extraordinary characteristics, like the ability to grow optimally at 300°C (572°F) and the capacity to metabolize a wide range of organic and inorganic materials."

These claims and data have yet to be verified and reported in any peer reviewed publication. In 2006 Louis and Kumar published a paper in Astrophysics and Space Science entitled "The red rain phenomenon of Kerala and its possible extraterrestrial origin"[3] which reiterated their hypothesis that the red rain was biological matter from an extraterrestrial source but made no mention of their previous claims to having induced the cells to grow. One of their conclusions was that if the red rain particles are biological cells and are of cometary origin, then this phenomena can be a case of cometary panspermia.[3] On August 2008 Louis and Kumar again presented their case in an astrobiology conference.[29] The abstract for paper states that

"The red cells found in the red rain in Kerala, India are now considered as a possible case of extraterrestrial life form. These cells can undergo rapid replication even at an extreme high temperature of 300 deg C. They can also be cultured in diverse unconventional chemical substrates. The molecular composition of these cells is yet to be identified".


Debris from a meteor would not have continued to fall in the same area over a period of two months, as it would have been dispersed by winds.

Samples of the red particles were also sent for analysis to Milton Wainwright at Sheffield University and Chandra Wickramasinghe at Cardiff University. Wickramasinghe reported in December 2006 that "work in progress has yielded positive for DNA, however, this identification is not yet fully confirmed, and might be considered equivocal".[30] The absence of DNA is key to Louis and Kumar's hypothesis that the cells were of extraterrestrial origins.[24] Wainwright is quoted as saying:[13]

“There appears to be an increasing tendency among scientists to come up with wild explanations when asked by the press to comment on unusual, novel phenomena. A good example is provided by comments about the recent Indian red rain phenomenon."

A correction was printed in The Observer[31] regarding Dr. Wainwright's comment that the red rain lacked DNA. Dr. Wainwright asked in the correction to make clear that he currently had no view on whether the samples contained genetic material or not, and that it was physicist Godfrey Louis who held that view.

The primary function of most spores's wall and impermeability is to ensure its own survival through periods of environmental stress. They are therefore resistant to ultraviolet and gamma radiation, desiccation, lysozyme, temperature, starvation and chemical disinfectants. Visualising spores under a light microscope can be difficult due to the impermeability of the ungerminated spore wall to dyes and stains used in cell biology methods.

The controversial conclusion of Louis et al. is the only hypothesis suggesting that these organisms are of extraterrestrial origin.[32] Louis has not reported the use of any standard microbiology growth medium to culture and induce germination and growth of the spores, basing his claim of "biological" growth on absorbance measurements following precipitation by supercritical fluids.[28]

Regarding the "absence" of DNA, Louis' only attempt to stain the spore's DNA was by the use of malachite green, which is generally used to stain bacterial endospores, not algal spores.[33] Visualising algal spore DNA under a light microscope can be difficult due to the impermeability of the highly resistant spore wall to dyes and stains used in normal staining procedures. In order to stain the spores' DNA, which is tightly packed, encapsulated and desiccated, spores must first be cutured in suitable growth medium and temperature in order to induce germination.

Further occurrences

Reports indicated that on August 21, 2007 red colored rainfall occurred in a few places in the northern part of Kozhikode district. Places around Vadakara, a municipality in Kozhikode district, which is 50 kilometers (31 miles) northward of Kozhikode town witnessed this phenomenon. The Center for Water Resources Development and Management (CWRDM) an Indian government agency, was reported to be awaiting samples for examination.[34]

A possibly related incident occurred in February 2008 when small fish started raining down during heavy rain in a village in Kerala.[35]


  1. ^ a b Gentleman, Amelia; Robin McKie (2006). "Red rain could prove that aliens have landed". Guardian Unlimited.,,1723913,00.html. Retrieved March 12, 2006.  
  2. ^ a b JULY 28, 2001, The Hindu: Multicolour rain
  3. ^ a b c d e f g h i j k l Louis, G.; Kumar A.S. (2006). "The red rain phenomenon of Kerala and its possible extraterrestrial origin". Astrophysics and Space Science 302: 175. doi:10.1007/s10509-005-9025-4. Retrieved 2008-06-06. "Full paper for a fee is available at ([1])".  
  4. ^ a b Ramakrishnan, Venkitesh (2001-07-30). "Colored rain falls on Kerala". BBC. Retrieved March 6, 2006.  
  5. ^ a b c d e f g h i j Sampath, S.; Abraham, T. K., Sasi Kumar, V., & Mohanan, C.N. (2001). "Colored Rain: A Report on the Phenomenon." (PDF). Cess-Pr-114-2001 (Center for Earth Science Studies and Tropical Botanic Garden and Research Institute). Retrieved August 30, 2009.  
  6. ^ a b Radhakrishnan, M. G. (2001). "Scarlets Of Fire". India Today. Retrieved March 6, 2006.  
  7. ^ Mystery of the scarlet rains and other talesTimes of India, 6 August 2001
  8. ^ Now wells form spontaneously in KeralaTimes of India, 5 August 2001 (from the Internet Archive)
  9. ^ DiGregorio, Barry E. (2007). "What made the rain red in India? Isotopic analysis points to a terrestrial origin for the unusual organic particles that colored the rain like blood." ( – Scholar search). Analytical Chemistry (Washington, DC, United States) 79 (9): 3238. Retrieved 2007-09-10. "My chemical tests are consistent with a terrestrial origin for this material. This doesn't mean it is not extraterrestrial, but it certainly does not support it".  
  10. ^ a b c "Red rain was fungus, not meteor". Indian Express. August 6, 2001. Retrieved 2008-05-31.  
  11. ^ "It's raining aliens"]. Retrieved 2008-06-03. "transcript of a New Scientist podcast"  
  12. ^ Benfield, Chris (3 June 2008). "Is mysterious ‘red rain’ first evidence of life in space?". Yorkshire Today. Retrieved 2008-06-03.  
  13. ^ a b 1 April 2006, New Scientist: Red rain fantasies
  14. ^ Lane, Megan (2000-08-07). "It's raining fish!". BBC. Retrieved 2006-03-06.  
  15. ^ Bücher, A and Lucas, C, 1984. Sédimentation éolienne intercontinentale, poussières sahariennes et géologie. Bull Centr Rech Explor Prod Elf-Aquitanie 8, pp. 151–165
  16. ^ Avila, Anna; Peñuelas, Josep (April), "Increasing frequency of Saharan rains over northeastern Spain and its ecological consequences", The Science of the Total Environment 228 (2-3): 153–156, doi:10.1016/S0048-9697(99)00041-8  
  17. ^ Mill H. R., R. K. G. Lempfert, 1904, The great dust fall of February 1903 and its origin. Quart. J. Roy. Meteorol. Soc. 30:57.
  18. ^ Satyanarayana, M.; Veerabuthiran S., Ramakrishna Rao D. Presennakumar B. (2004). "Colored Rain on the West Coastal Region of India: Was it Due to a Dust Storm". Aerosol Science and Technology 28: 24–26.  
  19. ^ Veerabuthiran, S.; Satyanarayana, M. (June 2003). "Lidar observations on atmospheric dust transported from south-west Asia to Indian west coast region: A case study of colour rain event occurred during July 2001". Indian Journal of Radio & Space Physics 32: 158–165. Retrieved 2008-05-30.  
  20. ^ Varma, M. Dinesh (September 1, 2001). "Theory links 'scarlet rain' to Mayon volcano". The Hindu. Retrieved 2008-05-26.  
  21. ^ "Mayon eruption status update June 2001". Retrieved 2008-05-26.  
  22. ^ "Jet Streams around the World". BBC Weather Centre. Retrieved 2008-05-26.  
  23. ^ McCafferty, Partick (2008). "Bloody rain again! Red rain and meteors in history and myth". International Journal of Astrobiology 7. doi:10.1017/S1473550407003904. Retrieved 2008-05-31.  
  24. ^ a b Louis, Godfrey; Kumar, A. Santhosh (5 October 2003). "Cometary panspermia explains the red rain of Kerala". arXiv. Retrieved 2008-06-01.  
  25. ^ "'Extraterrestrial Life' in Red Rain of Kerala". Earthfiles. August 6, 2006. Retrieved 2009-10-11.  
  26. ^ "Red rain cell research: A new perspective for interplanetary transfer of life." EPSC Abstracts, Vol. 4, EPSC2009-707-1, 2009. European Planetary Science Congress.
  27. ^ "An optical spectroscopic study correlating the yellow rain and cultured red rain microbes." Proc. SPIE, Vol. 7441, 74410N (11 September 2009); doi:10.1117/12.826780
  28. ^ a b Louis, Godfrey; Kumar, A. Santhosh (29 December 2003). "New biology of red rain extremophiles prove cometary panspermia". arXiv. Retrieved 2008-06-01.  
  29. ^ Godfrey Louis and A. Santhosh Kumar. "Unusual autofluorescence of cultured red-rain cells". SPIE Symposium, San Diego, California 2008. Retrieved 2009-09-01.  
  30. ^ "Cardiff Centre of Astrobiology: Analysis of Red Rain of Kerala". University of Cardiff. Retrieved 2008-06-24.  
  31. ^ For the record, The Observer, March 12, 2006
  32. ^ Louis, Godfrey. "Home Page of Dr. Godfrey Louis". Retrieved 2009-08-30.  
  33. ^ Mayberry, William (4/7/2004). "Spore Stain Tutorial". American Society for Microbiology. Retrieved 2009-08-31.  
  34. ^ Latest India News @ NewKerala.Com, India
  35. ^ "‘Fish rain’ takes Kerala villagers by surprise". The Financial Express. , February 12, 2008. Retrieved 2008-05-27.  

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