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{{Short description|Episodes of rain containing vast amounts of red algal spores in India}}
'''Red rain in Kerala''' was a phenomenon observed over several weeks beginning in July ] in the southern ]n state of ]. Heavy downpours occurred in which the rain was bright red, staining clothes and burning leaves on trees.
{{Other uses|Red rain (disambiguation){{!}}Red Rain}}
{{EngvarB|date=September 2013}}
{{Use dmy dates|date=November 2020}}
]


The''' Kerala red rain phenomenon''' was a ] event that occurred in ] of southern Indian state ] on Monday, 15 July 1957 and the colour subsequently turned yellow<ref>https://eparlib.nic.in/bitstream/123456789/1523/1/lsd_02_02_06-08-1957.pdf p. 25</ref> and also 25 July to 23 September 2001, when heavy downpours of red-coloured rain fell sporadically in Kerala, staining clothes pink.<ref name="gentleman">{{cite news | last1=Gentleman | first1=Amelia | last2=McKie | first2=Robin | url=http://observer.guardian.co.uk/world/story/0,,1723913,00.html | title=Red rain could prove that aliens have landed | work=] | access-date=12 March 2006 | date=5 March 2006 | url-status=live | archive-url=https://web.archive.org/web/20060320081014/http://observer.guardian.co.uk/world/story/0,,1723913,00.html | archive-date=20 March 2006}}</ref> Yellow, green and black rain was also reported.<ref name=hinduonet>{{cite web |url=http://www.hinduonnet.com/thehindu/2001/07/29/stories/0229000p.htm |title=JULY 28, 2001, The Hindu: Multicolour rain |publisher=Hinduonnet.com |date=2001-07-29 |access-date=2015-10-18 |url-status=usurped |archive-url=https://web.archive.org/web/20100906145123/http://www.hinduonnet.com/thehindu/2001/07/29/stories/0229000p.htm |archive-date=6 September 2010}}</ref><ref name="L&K 2006"/><ref name=BBC/> Coloured rain was also reported in Kerala in 1896 and several times since,<ref name=CESS/> most recently in June 2012,<ref name=Kannur>{{cite news | title = Morning shower paints rural Kannur red | date = 29 June 2012 | url = https://timesofindia.indiatimes.com/city/kozhikode/Morning-shower-paints-rural-Kannur-red/articleshow/14477858.cms | archive-url = https://web.archive.org/web/20130921113613/http://articles.timesofindia.indiatimes.com/2012-06-29/kozhikode/32472196_1_kannur-red-rain-rainwater | url-status = live | archive-date = 21 September 2013 | work = ] | access-date = 20 July 2012}}</ref> and from 15 November 2012 to 27 December 2012 in eastern and north-central provinces of ].<ref>{{cite web |url=http://www.fabpretty.com/mystery/red-rain-in-sri-lanka-in-2012/ |title=Red Rain in Sri Lanka in 2012 |publisher=Fabpretty.com |date=2012-12-31 |access-date=2015-10-18 |url-status=live |archive-url=https://web.archive.org/web/20151020052548/http://www.fabpretty.com/mystery/red-rain-in-sri-lanka-in-2012/ |archive-date=20 October 2015}}</ref><ref>{{cite web |author=Gamini Gunaratna, Sri Lanka News Paper by LankaPage.com (LLC) |url=http://www.colombopage.com/archive_12B/Nov16_1353054110CH.php |title=Sri Lanka to investigate the cause of red rain received in some parts |publisher=Colombopage.com |date=2012-11-16 |access-date=2015-10-18 |url-status=live |archive-url=https://web.archive.org/web/20150923205557/http://www.colombopage.com/archive_12B/Nov16_1353054110CH.php |archive-date=23 September 2015}}</ref><ref>{{cite web |url=http://www.dailynews.lk/2012/11/17/news14.asp |title=No meteoritic or alien connection with Red rain |publisher=Dailynews.lk |date=2012-11-17 |access-date=2015-10-18 |url-status=dead |archive-url=https://web.archive.org/web/20121119001114/http://www.dailynews.lk/2012/11/17/news14.asp |archive-date=19 November 2012}}</ref><ref>Chandra Wickramasinghe says yellow rain is young red rain before growth: </ref>
A convincing explanation for the phenomenon has yet to be found. Initially it was suspected that like many instances of coloured rain, dust transported from elsewhere was responsible, but the distribution of the red rain was patchy whereas a dust layer would be expected to be evenly distributed. Scientists at the ] in ] have proposed a far more outlandish theory - that the dust is in fact composed of ] matter of ] origin. If this were to be proven, it would be the first direct evidence in favour of the theory of ], which posits that life on Earth arrived here from ].


Following a light-microscopy examination in 2001, it was initially thought that the rains were coloured by fallout from a hypothetical ] ],<ref name=CESS/> but a study commissioned by the ] concluded that the rains had been coloured by airborne ]s from a locally prolific terrestrial green algae from the ] '']''.<ref name=CESS >{{cite journal| last=Sampath| first=S.| author2=Abraham, T. K| author3=Sasi Kuma| author4=V.| author5=Mohanan, C.N.| name-list-style=amp| title=Coloured Rain: A Report on the Phenomenon| journal= Cess-Pr-114-2001| publisher=Center for Earth Science Studies and Tropical Botanic Garden and Research Institute | date=2001| url=http://www.geocities.com/iamgoddard/Sampath2001.pdf|access-date =30 August 2009|archive-url=https://web.archive.org/web/20060613135746/http://www.geocities.com/iamgoddard/Sampath2001.pdf |archive-date=13 June 2006}}</ref>
==The rain==


==Occurrence==
The red rain in Kerala first fell on ] ], in the districts of ] and ] in the southern part of the state. As well as red rain, some reports suggested that other colours of rain were also seen . Many more occurrences of the red rain were reported over the following 10 days, and with diminshing frequency until the end of September.
] in Kerala, which experienced the most red rainfall]]
The coloured rain of Kerala began falling on 25 July 2001, in the districts of Kottayam and ] in the southern part of the state. Yellow, green, and black rain was also reported.<ref name=hinduonet/><ref name="L&K 2006"/><ref name=BBC>{{cite news | author = Venkatraman Ramakrishnan | url = http://news.bbc.co.uk/1/hi/world/south_asia/1465036.stm | title = Colored rain falls on Kerala | publisher = BBC | access-date = 6 March 2006 | date = 30 July 2001 | url-status = live | archive-url = https://web.archive.org/web/20060515220912/http://news.bbc.co.uk/1/hi/world/south_asia/1465036.stm | archive-date = 15 May 2006| author-link = Venkatraman Ramakrishnan }}</ref> Many more occurrences of the red rain were reported over the following ten days, and then with diminishing frequency until late September.<ref name="L&K 2006"/> According to locals, the first coloured rain was preceded by a loud ]clap and flash of light, and followed by groves of trees shedding shrivelled grey "burnt" leaves. Shriveled leaves and the disappearance and sudden formation of ] were also reported around the same time in the area.<ref name="indiatoday">{{cite web | last = Radhakrishnan | first = M. G. | date = 2001 | url = http://www.indiatoday.com/webexclusive/dispatch/20010905/stephen.html | title = Scarlets of Fire | work = India Today| access-date = 6 March 2006
|archive-url = https://web.archive.org/web/20041226194558/http://www.indiatoday.com/webexclusive/dispatch/20010905/stephen.html |archive-date = 26 December 2004}}</ref><ref name="timesofindia 20010806"> – ], 6 August 2001</ref><ref name="timesofindia 20010805"> – ], 5 August 2001 (from the ])</ref> It typically fell over small areas, no more than a few square kilometres in size, and was sometimes so localised that normal rain could be falling just a few meters away from the red rain. Red rainfalls typically lasted less than 20 minutes.<ref name="L&K 2006">{{cite journal | author1 =Godfrey Louis | author2 =A. Santhosh Kumar | date =2006 | title =The red rain phenomenon of Kerala and its possible extraterrestrial origin | journal =Astrophysics and Space Science | volume =302 | issue =1–4 | pages =175–87 | arxiv =astro-ph/0601022 | doi =10.1007/s10509-005-9025-4 | bibcode =2006Ap&SS.302..175L | s2cid =119427737| author1-link =Godfrey Louis }}</ref> Each millilitre of rain water contained about 9 million red particles. ] these figures to the total amount of red rain estimated to have fallen, it was estimated that {{convert|50000|kg|lb}} of red particles had fallen on Kerala.<ref name="L&K 2006"/>


==Description of the particles==
The coloration of the rain was due to red particles in ] in the rain water. When it fell, the red rain was at times as strongly coloured as ]. It typically fell over small areas, no more than a few ]s in size, and was sometimes so localised that normal rain could be falling just a few metres away from red rain. Red rain falls typically lasted less than 20 minutes {{ref|Louis}}.
The brownish-red solid separated from the red rain consisted of about 90% round red particles and the balance consisted of debris.<ref name=CESS/> The particles in ] in the rain water were responsible for the colour of the rain, which at times was strongly coloured red. A small percentage of particles were white or had light yellow, bluish grey and green tints.<ref name="L&K 2006"/> The particles were typically 4 to 10 ] across and spherical or oval. ] images showed the particles as having a depressed centre. At still higher magnification some particles showed internal structures.<ref name="L&K 2006"/>


== Chemical composition ==
==Conventional explanations==
{| class="wikitable" style="float: right; text-align: centre; margin: 1em; margin-top: 0;"
|+ Elemental analysis
|-
|
! scope="col" style="width:100px;"| Analysis by the CESS <br />(%)
! scope="col" style="width:100px;"| Analysis by Louis & Kumar (%)
|-
! scope="row" style="width:30px;"| ]
| 1.0
| 0.41
|-
! scope="row" | ]
| 2.52
|
|-
! scope="row" | ]
| 51.00
| 49.53
|-
! scope="row" | ]
|
| 0.12
|-
! scope="row" | ]
|
| 4.43
|-
! scope="row" | ]
| 0.61
| 0.97
|-
! scope="row" | ]
| 1.48
|
|-
! scope="row" | ]
|
| 1.84
|-
! scope="row" | ]
|
| 45.42
|-
! scope="row" | ]
| 0.26
|
|-
! scope="row" | ]
| 0.08
|
|-
! scope="row" | ]
| 7.50
| 2.85
|-
! scope="row" | ]
| 0.49
| 0.69
|}
] of particles from red rain sample]]


Some water samples were taken to the ] (CESS) in India, where they separated the suspended particles by filtration. The ] of the water was found to be around 7 (neutral). The ] of the rainwater showed the absence of any dissolved ]. Sediment (red particles plus debris) was collected and analysed by the CESS using a combination of ion-coupled plasma ], atomic absorption spectrometry and wet chemical methods. The major elements found are listed below.<ref name=CESS /> The CESS analysis also showed significant amounts of ], including nickel (43 ]), ] (59 ppm), ] (321 ppm), ] (67ppm) and copper (55 ppm).
Throughout history, unusual objects have fallen with the rain - in ] a small ] sucked up a school of ] a mile out to sea, depositing them shortly afterwards on ] in the ] . Coloured rain is by no means rare, and can often be explained by the transport of ] from ] regions. One such case occurred in ] in ], when dust was carried from the ] and fell with rain in February of that year.


Physicists ] and Santhosh Kumar of the ], Kerala, used ] analysis of the red solid and showed that the particles were composed of mostly carbon and oxygen, with trace amounts of silicon and iron.<ref name="L&K 2006" /> A ] showed content of 43.03% carbon, 4.43% hydrogen, and 1.84% nitrogen.<ref name="L&K 2006" />
At first, the red rain in Kerala was attributed to the same effect, with dust from the deserts of ] initially the suspect. ] observations had detected a cloud of dust in the atmosphere near Kerala in the days preceding the outbreak of the red rain {{ref|Satyanarayana}}. However, this hypothesis could not explain certain aspects of the red rain, such as its sudden onset and gradual decline over two months, its localisation to Kerala despite atmospheric conditions that should have seen it occur in neighbouring states as well, and the unusual nature of the red particles, discussed below.


] in the Division of Nutritional Sciences at ] conducted carbon and nitrogen isotope analyses using a scanning electron microscope with X-ray micro-analysis, an elemental analyser, and an isotope ratio (IR) mass spectrometer. The red particles collapsed
==Less conventional explanation==
when dried, which suggested that they were filled with fluid. The ] in the particles were analysed and seven were identified (in order of concentration): ], ]/], ], ], ], and ]. The results were consistent with a marine origin or a terrestrial plant that uses a ] photosynthetic pathway.<ref name="isotope">{{cite journal |last=DiGregorio |first=Barry E. |date=2007 |title=What made the rain red in India? Isotopic analysis points to a terrestrial origin for the unusual organic particles that coloured the rain like blood. |journal=Analytical Chemistry |volume=79 |issue=9 |page=3238 |doi=10.1021/ac071901u |pmid=17523227 |quote=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.|doi-access= }}</ref>


== Government report ==
A more radical explanation for the rains was proposed by Godfrey Louis and A. Santhosh Kumar, two scientists at ] in ], Kerala. Samples of the rainwater were collected at many locations, allowing the red particles to be collected and analysed, and Louis and Kumar found that the red particles did not look like dust but instead had the appearance of biological cells. Chemical analyses showed instead that they seemed to be ] material, and the scientists proposed that the dust may be ]s of ] origin.
], purportedly showing a detached inner capsule.]]
Initially, the ] (CESS) stated that the likely cause of the red rain was an exploding meteor, which had dispersed about 1,000&nbsp;kg (one ton) of material. A few days later, following a basic ] evaluation, the CESS retracted this as they noticed the particles resembled spores,<ref name='Rense'>{{cite news |last=Surendran |first=P.K. |url=http://www.rense.com/general28/scart.htm |title=Sonic Booms Adds To India 'Scarlet Rains' Mystery |work=Rense |date=22 August 2002 |access-date=2015-06-11 |url-status=live |archive-url=https://web.archive.org/web/20150721001800/http://www.rense.com/general28/scart.htm |archive-date=21 July 2015}}</ref><ref name=fungus>{{cite news |title=Red rain was fungus, not meteor |url=http://indianexpress.com/?s=Red+rain+was+fungus%2C+not+meteor |work=The Indian Express |date=6 August 2001 |access-date=31 May 2008 |url-status=live |archive-url=https://web.archive.org/web/20150613061554/http://indianexpress.com/?s=Red+rain+was+fungus%2C+not+meteor |archive-date=13 June 2015}}</ref><ref>{{cite journal | doi = 10.1029/2002EO000250 | volume=83 | title=Colored rain falls in Kerala, India | year=2002 | journal=Eos, Transactions American Geophysical Union | page=335 | last1 = Kumar | first1 = V. Sasi| issue=31 | doi-access=free }}</ref> 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 ] (TBGRI) for ] 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 cultures were observed under a microscope.<ref name="report">{{cite web |url=http://www.bibliotecapleyades.net/ciencia/ciencia_kerala12.htm |title=Coloured Rain – A report on the Phenomenon |date=2001 |access-date=2015-06-11 |url-status=live |archive-url=https://web.archive.org/web/20150718080031/http://www.bibliotecapleyades.net/ciencia/ciencia_kerala12.htm |archive-date=18 July 2015}}</ref>


In November 2001, commissioned by the ]'s Department of Science & Technology, the Centre for Earth Science Studies (CESS) and the Tropical Botanical Garden and Research Institute (TBGRI) issued a joint report, which concluded:<ref name=CESS/><ref name=fungus/>
Louis and Kumar's analysis found that the red particles were typically 4-10&micro;m across, spherical or oval in shape, and similar in appearance to ]s. On average, 1 ] of rain water was found to contain 9 million red particles, and the weight of particles in 1 ] was about 100 ]s. Extrapolating these figures to the total amount of red rain estimated to have fallen, Louis and Kumar calculated that a total weight of some 50,000 ]s of red particles had fallen over Kerala.


{{quotation|The colour was found to be due to the presence of a large amount of spores of a ]-forming ] belonging to the genus '']''. Field verification showed that the region had plenty of such lichens. Samples of lichen taken from ] area, when cultured in an algal growth 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}}
Chemical analyses showed that the particles were predominantly made of ] and ], with small amounts of ], ], ], ] and ] also detected. Louis and Kumar performed tests to see if any ] or ] was present in the red particles, but found none.
]'' on '']'' bark]]
The site was again visited on 16 August 2001 and it was found that almost all the trees, rocks and even lamp posts in the region were covered with ''Trentepohlia'' estimated to be in sufficient amounts to generate the quantity of spores seen in the rainwater.<ref name=CESS/> Although red or orange, ''Trentepohlia'' is a ] green alga which can grow abundantly on tree bark or damp soil and rocks, but is also the photosynthetic ] or photobiont of many lichens, including some of those abundant on the trees in Changanassery area.<ref name=CESS/> The strong orange colour of the algae, which masks the green of the ], is caused by the presence of large quantities of orange ] pigments. A ] is not a single organism, but the result of a partnership (]) between a fungus and an alga or cyanobacterium.


The report also stated that there was no meteoric, volcanic or desert dust origin present in the rainwater and that its colour was not due to any dissolved gases or pollutants.<ref name=CESS/> 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.<ref name=CESS/> 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 colour in the rainfall has been identified, finding the answers to these questions is a challenge."<ref name=fungus/> Attempting to explain the unusual spore proliferation and dispersal, researcher Ian Goddard proposed several local atmospheric models.<ref>{{cite journal | title = The Coloured Rains of Kerala: An Exploration of Possible Causal Mechanisms | journal = Noesis – the Journal of the Mega Society | date = March 2006 | author = Ian Goddard | issue = 180 | url = http://megasociety.org/noesis/180.htm#Coloured_Rains | access-date = 2 October 2012 | url-status = live | archive-url = https://web.archive.org/web/20120731080501/http://megasociety.org/noesis/180.htm#Coloured_Rains | archive-date = 31 July 2012}}</ref>
==Possibly cometary origin==


Parts of the CESS/TBGRI report were supported by ] at the ], who, together with ], has studied ] ]s.<ref name="gentleman"/><ref name="tmcnet 2006">{{cite web|url=http://www.tmcnet.com/usubmit/2006/03/03/1427866.htm|title=It's raining aliens |access-date=3 June 2008|url-status=live|archive-url=https://web.archive.org/web/20080830000344/http://www.tmcnet.com/usubmit/2006/03/03/1427866.htm|archive-date=30 August 2008}}</ref> In March 2006 Wainwright said the particles were similar in appearance to spores of a ],<ref name="yorkshire">{{cite news |first=Chris |last=Benfield |title=Is mysterious 'red rain' first evidence of life in space? |url=http://www.yorkshiretoday.co.uk/ViewArticle2.aspx?SectionID=55&ArticleID=1375334 |publisher=Yorkshire Today |date=3 June 2008 |access-date=3 June 2008 |url-status=dead |archive-url=https://web.archive.org/web/20070112041546/http://www.yorkshiretoday.co.uk/ViewArticle2.aspx?SectionID=55&ArticleID=1375334 |archive-date=12 January 2007}}</ref> later saying that he had confirmed the presence of ],<ref name="David Darling's Newsletter #39"> {{webarchive |url=https://web.archive.org/web/20130921170203/http://www.daviddarling.info/discussion/newsletters_past_39.html |date=21 September 2013 }}</ref> and reported their similarity to algal spores, and found no evidence to suggest that the rain contained dust, sand, fat globules, or blood. In November 2012, Rajkumar Gangappa and Stuart Hogg from the ], UK, confirmed that the red rain cells from Kerala contain DNA.<ref name='Rajkumar Gangappa and Stuart Hogg'>{{cite journal | title = DNA unmasked in the red rain cells of Kerala | journal = Microbiology | date = 22 November 2012 | first1 = Rajkumar Gangappa | author2 = Stuart Hogg | doi = 10.1099/mic.0.062711-0 | url = http://mic.sgmjournals.org/content/early/2012/11/16/mic.0.062711-0.abstract | access-date = 5 December 2012 | pmid = 23175506 | volume = 159 | issue = Pt 1 | pages = 107–11 | last1 = Gangappa | doi-access = free | url-status = live | archive-url = https://web.archive.org/web/20121212071538/http://mic.sgmjournals.org/content/early/2012/11/16/mic.0.062711-0.abstract | archive-date = 12 December 2012}}</ref>
A few hours before the first occurrence of the red rain, a ] was reported by residents of ] in Kottayam district, accompanied by a flash of light. Louis and Kumar suggest that this was caused by the disintegration of a small ] entering the Earth's atmosphere, and that this comet contained large quantities of the red particles. Observations show that 85% of the red rain fell within 10 days of ], and Louis and Kumar suggest that this is consistent with the settling of red particles released into the upper atmosphere by a cometary break-up. An initial study of the red particles by scientists in ] suggested that they could be dust from a comet, but subsequent observations found that the particles did not look like dust under close scrutiny .


In February 2015, a team of scientists from India and Austria, also supported the identification of the algal spores as '']'', however, they speculate that the spores from the 2011 incident were carried by winds from Europe to the Indian subcontinent.<ref name="European alga">{{cite news |last=Nandakumar |first=T. |title=2011 red rain caused by European species of alga: experts |work=The Hindu |date=28 March 2015 }}</ref>
Louis and Kumar further suggest that the particles are s and thus represent evidence of extraterrestrial life. If the particles are biological in nature and did originate in a comet, it would be the first evidence in favour of the theory of ], in which life on Earth is proposed to have been carried here from elsewhere in the ]. ] and ] have been among the proponents of the theory but it has never found much of a following, being dismissed by most mainstream scientists. Further tests on the particles are currently being carried out at ].


== Alternative hypotheses ==
==References==
History records many instances of unusual objects falling with the rain – in 2000, in an example of ], a small ] in the ] sucked up a school of fish a mile off shore, depositing them shortly afterwards on ] in the United Kingdom.<ref>{{cite news | last = Lane | first = Megan | date = 7 August 2000 | url = http://news.bbc.co.uk/1/hi/uk/869482.stm | title = It's raining fish! | publisher = BBC | access-date = 6 March 2006 | url-status = live | archive-url = https://web.archive.org/web/20070830153056/http://news.bbc.co.uk/1/hi/uk/869482.stm | archive-date = 30 August 2007}}</ref> Coloured rain is by no means rare, and can often be explained by the airborne transport of ] from ] or other dry regions which have been washed down by rain. "Red Rains" have been frequently described in southern Europe, with increasing reports in recent years.<ref name="Bücher">
Bücher, A and Lucas, C, 1984. Sédimentation éolienne intercontinentale, poussières sahariennes et géologie. Bull Centr Rech Explor Prod Elf-Aquitanie 8, pp. 151–65</ref><ref>
{{Cite journal
| last1 = Avila
| first1 = Anna
| last2 = Peñuelas
| first2 = Josep
| title = Increasing frequency of Saharan rains over northeastern Spain and its ecological consequences
| journal = The Science of the Total Environment
| volume = 228
| issue = 2–3
| pages = 153–56
| date = April 1999
| doi = 10.1016/S0048-9697(99)00041-8
| bibcode = 1999ScTEn.228..153A
}}</ref> One such case occurred in England in 1903, when dust was carried from the ] and fell with rain in February of that year.<ref name="english_rain">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.</ref>


At first, the red rain in Kerala was attributed to the same effect, with dust from the deserts of ] initially the suspect.<ref name="indiatoday"/> ] observations had detected a cloud of dust in the atmosphere near Kerala in the days preceding the outbreak of the red rain.<ref name="Satyanarayana">{{cite journal | last =Satyanarayana | first =M. | author2 =Veerabuthiran S. | author3 =Ramakrishna Rao | author4 =D. Presennakumar B. | date =2004 | title =Colored Rain on the West Coastal Region of India: Was it Due to a Dust Storm | url =https://www.researchgate.net/publication/233339558 | journal =Aerosol Science and Technology | volume =28 | issue =1 | pages =24–26 | doi =10.1080/02786820300981 | doi-broken-date =1 November 2024 | bibcode =2004AerST..38...24S | url-status =live | archive-url =https://web.archive.org/web/20160115021906/https://www.researchgate.net/publication/233339558_Colored_Rain_on_the_West_Coastal_Region_of_India_Was_it_Due_to_a_Dust_Storm | archive-date =15 January 2016}}</ref><ref>{{cite journal | last =Veerabuthiran | first =S. | author2 =Satyanarayana, M. | date =June 2003 | title =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 | journal =Indian Journal of Radio & Space Physics | volume =32 | pages =158–65 | url =http://www.niscair.res.in/sciencecommunication/ResearchJournals/rejour/ijrsp/ijrsp2k3/ijrsp_jun03.htm#p6 | access-date =30 May 2008 | url-status =live | archive-url =https://web.archive.org/web/20051028183349/http://www.niscair.res.in/ScienceCommunication/ResearchJournals/rejour/ijrsp/ijrsp2k3/ijrsp_jun03.htm#p6 | archive-date =28 October 2005}}</ref> However, laboratory tests from all involved teams ruled out the particles were desert sand.<ref name="Satyanarayana"/>
*{{note|Satyanarayana}} 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, v.38, p.24–26

*{{note|Louis}} Louis G., Kumar A.S. (2006), ''The red rain phenomenon of Kerala and its possible extraterrestrial origin'', accepted for publication in ''Astrophysics & Space Science''
K.K. Sasidharan Pillai, a senior scientific assistant in the Indian Meteorological Department, proposed dust and acidic material from an eruption of ] in the Philippines as an explanation for the coloured rain and the "burnt" leaves.<ref>{{cite news | last = Varma | first = M. Dinesh | title = Theory links 'scarlet rain' to Mayon volcano | work = The Hindu | date = 1 September 2001 | url = http://www.hinduonnet.com/2001/09/01/stories/0401211v.htm | access-date = 26 May 2008 | url-status = usurped | archive-url = https://web.archive.org/web/20080329131315/http://www.hinduonnet.com/2001/09/01/stories/0401211v.htm | archive-date = 29 March 2008 }}</ref> The volcano was erupting in June and July 2001<ref>{{cite web|url=http://www.reliefweb.int/rw/rwb.nsf/AllDocsByUNID/5ef2040d3ff5114cc1256a76005478c6|archive-url=https://archive.today/20050118112137/http://www.reliefweb.int/rw/rwb.nsf/AllDocsByUNID/5ef2040d3ff5114cc1256a76005478c6|url-status=dead|archive-date=18 January 2005|title=Mayon eruption status update June 2001|access-date=26 May 2008}}</ref> and Pillai calculated that the Eastern or Equatorial ] could have transported volcanic material to Kerala in 25–36 hours. The Equatorial jet stream is unusual in that it sometimes flows from east to west at about 10° N,<ref>{{cite web| url=http://www.skybrary.aero/index.php/Jet_Stream| title=Jet Stream| publisher=SKYbrary| access-date=30 October 2015| url-status=live| archive-url=https://web.archive.org/web/20150925231142/http://www.skybrary.aero/index.php/Jet_Stream| archive-date=25 September 2015}}</ref> 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.<ref name=CESS/>

A study has been published showing a correlation between historic reports of coloured rains and of meteors;<ref name=mmcaf>{{cite journal | last =McCafferty | first =Partick | date =2008 | title =Bloody rain again! Red rain and meteors in history and myth | journal =International Journal of Astrobiology | volume =7 | issue =1 | doi =10.1017/S1473550407003904 | bibcode =2008IJAsB...7....9M | page =9| s2cid =123656159 }}</ref> the author of the paper, Patrick McCafferty, stated that sixty of these colored rain events, or 36%, were linked to meteoritic or cometary activity, though not always strongly. Sometimes the fall of red rain seems to have occurred after an air-burst, 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.<ref> {{webarchive |url=https://web.archive.org/web/20160305022142/http://www.world-science.net/exclusives/080122_red-rain.htm |date=5 March 2016 }}. ''World Science''. 22 January 2008</ref>

===Panspermia hypothesis===

In 2003 ] and Santhosh Kumar, physicists at the ] in ], Kerala, posted an article entitled "Cometary ] explains the red rain of Kerala"<ref name=L&K2003a>{{cite arXiv |eprint=astro-ph/0310120 |title= Cometary panspermia explains the red rain of Kerala |last= Louis |first=Godfrey |author2= Kumar, A. Santhosh |date=5 October 2003}}</ref> in the non-]ed ] web site. While the CESS report said there was no apparent relationship between the loud sound (possibly a ]) 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 by winds.

Their work indicated that the particles were of biological origin (consistent with the CESS report), however, they invoked the ] ] to explain the presence of ] in a supposed fall of meteoric material.<ref name=chandra>{{cite news |title='Extraterrestrial Life' in Red Rain of Kerala |url=http://www.bibliotecapleyades.net/ciencia/ciencia_kerala11.htm |publisher=Earthfiles |date=6 August 2006 |access-date=11 October 2009 |url-status=live |archive-url=https://web.archive.org/web/20090908131321/http://www.bibliotecapleyades.net/ciencia/ciencia_kerala11.htm |archive-date=8 September 2009}}</ref><ref>{{cite web |url=http://meetingorganizer.copernicus.org/EPSC2009/EPSC2009-707-1.pdf |title="Red rain cell research: A new perspective for interplanetary transfer of life." EPSC Abstracts, Vol. 4, EPSC2009-707-1, 2009. European Planetary Science Congress. |access-date=2015-10-18 |url-status=live |archive-url=https://web.archive.org/web/20150402113206/http://meetingorganizer.copernicus.org/EPSC2009/EPSC2009-707-1.pdf |archive-date=2 April 2015}}</ref><ref>{{cite journal | doi = 10.1117/12.826780 | title=An optical spectroscopic study correlating the yellow rain and cultured red rain microbes | year=2009 | journal=Instruments and Methods for Astrobiology and Planetary Missions XII | last1 = Kumar | first1 = A. Santhosh| volume=7441 | pages=74410N | bibcode=2009SPIE.7441E..0NK | s2cid=123070754 | editor4-first=Kurt D | editor4-last=Retherford | editor3-first=Alexei Y | editor3-last=Rozanov | editor2-first=Gilbert V | editor2-last=Levin | editor1-first=Richard B | editor1-last=Hoover }}</ref> Additionally, using ] they were unable to detect ] or ] 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"<ref name=L&K2003b>{{cite arXiv |eprint=astro-ph/0312639|title= New biology of red rain extremophiles prove cometary panspermia |last= Louis |first=Godfrey |author2= Kumar, A. Santhosh |date=29 December 2003 }}</ref> in which they reported that
<blockquote>The microorganism isolated from the red rain of Kerala shows very extraordinary characteristics, like the ability to grow optimally at {{cvt|300|°C}} and the capacity to metabolise a wide range of organic and inorganic materials.
</blockquote>
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 '']'' entitled "The red rain phenomenon of Kerala and its possible extraterrestrial origin"<ref name="L&K 2006"/> which reiterated their arguments 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. The team also observed the cells using ] fluorescence microscopy, and they concluded that: "The fluorescence behaviour of the red cells is shown to be in remarkable correspondence with the extended red emission observed in the ] and other galactic and extragalactic ], suggesting, though not proving an extraterrestrial origin."<ref name=121oC>{{cite book | title = Instruments, Methods, and Missions for Astrobiology XIII | journal = Proceedings of the SPIE | date = 29 August 2010 | first = Rajkumar |last= Gangappa |author2=Chandra Wickramasinghe |author3=Milton Wainwright |author4=A. Santhosh Kumar |author5=Godfrey Louis | chapter = Growth and replication of red rain cells at 121°C and their red fluorescence | bibcode = 2010SPIE.7819E..0NG | volume = 7819 | page = 18 | doi = 10.1117/12.876393 | editor1-last = Hoover | editor1-first = Richard B | editor2-last = Levin | editor2-first = Gilbert V | editor3-last = Rozanov | editor3-first = Alexei Y | editor4-last = Davies | editor4-first = Paul C. W.|arxiv = 1008.4960 | s2cid = 118437731 }}</ref> One of their conclusions was that if the red rain particles are biological cells and are of cometary origin, then this phenomenon can be a case of cometary ].<ref name="L&K 2006"/>

In August 2008 Louis and Kumar again presented their case in an astrobiology conference.<ref>{{cite web |author=Godfrey Louis |author2=A. Santhosh Kumar |name-list-style=amp |title=Unusual autofluorescence of cultured red-rain cells |date=28 August 2008 |volume=7097 |pages=307–315 |url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7097/1/Unusual-autofluorescence-characteristic-of-cultured-red-rain-cells/10.1117/12.794041.short |access-date=1 September 2009 |publisher=SPIE Symposium, San Diego, California 2008|doi=10.1117/12.794041 }}</ref> The abstract for their paper states that <blockquote>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 {{cvt|300|°C}}. They can also be cultured in diverse unconventional chemical substrates. The molecular composition of these cells is yet to be identified.</blockquote>
In September 2010 a similar paper was presented at a conference in California, US.<ref>{{Cite book | last1 = Louis | first1 = Godfrey | author2 = A. Santhosh Kumar | title = Instruments, Methods, and Missions for Astrobiology XIII | journal = Proceedings of the SPIE | publisher = Proc. SPIE Vol. 7819, 78190R | place = San Diego, California | date = 7 September 2010 | page = 78190R | doi = 10.1117/12.860807 | others = Richard B. Hoover, Gilbert V. Levin, Alexei Y. Rozanov, Paul C.W. Davies (editors) | chapter = Growth characteristics of red rain microbes at temperatures below 100 °C | editor4-first = Paul C. W | editor4-last = Davies | editor3-first = Alexei Y | editor3-last = Rozanov | editor2-first = Gilbert V | editor2-last = Levin | editor1-first = Richard B | editor1-last = Hoover | volume = 7819 | bibcode = 2010SPIE.7819E..0RL | s2cid = 120685022 }}</ref>

====Cosmic ancestry====
Researcher ] used Louis and Kumar's "extraterrestrial origin" claim to further support his ] hypothesis called cosmic ancestry.<ref> {{webarchive |url=https://web.archive.org/web/20161109222710/http://www.panspermia.org/thirdalt.htm |date=9 November 2016 }}. Published in Darwinism, Design, and Public Education (2003)</ref> This hypothesis postulates that life is neither the product of ], nor is it spontaneously generated through ], but that it has always existed in the ]. Cosmic ancestry speculates that higher life forms, including intelligent life, descend ultimately from pre-existing life which was at least as advanced as the descendants.<ref>{{cite book|author1=Fred Hoyle|author2=Chandra Wickramasinghe|title=Evolution from Space|url=https://books.google.com/books?id=ccjjGAAACAAJ|year=1984|publisher=Touchstone|isbn=978-0-671-49263-2}}</ref><ref>
''Our Place in the Cosmos: The Unfinished Revolution'' by Wickramasinghe and Hoyle. (1993)</ref><ref>''Evolution From Space (The Omni Lecture) and Other Papers on the Origin of Life''. By Fred Hoyle (Enslow; Hillside, NJ; 1982)</ref><ref> {{webarchive |url=https://web.archive.org/web/20160304092535/http://www.skeptictank.org/figlie.htm |date=4 March 2016 }}. By Alec Grynspan ( 9 November 1997)</ref><ref>''Emergence of Life on Earth: A Historical and Scientific Overview''. By Iris Fry. Rutgers University Press, 2000. {{ISBN?}}</ref>

==== Criticism ====
Louis and Kumar made their first publication of their finding on a web site in 2003, and have presented papers at conferences and in astrophysics magazines a number of times since. The controversial conclusion of Louis et al. is the only hypothesis suggesting that these organisms are of extraterrestrial origin.<ref name=Homepage/> Such reports have been popular in the media, with major news agencies like CNN repeating the panspermia theory without critique.<ref name='Dunning'>{{Skeptoid|id=4224|number=224 | title = Alien Downpour: The Red Rain of India|date=21 September 2010 | access-date = 5 October 2012}}</ref>

The hypothesis' authors – G. Louis and Kumar – did not explain how debris from a meteor could have continued to fall on the same area over a period of two months, despite the changes in climatic conditions and wind pattern spanning over two months.<ref name=L&K2003a /><ref>{{cite web |author=moishecallow |url=http://www.environmentalgraffiti.com/meteorology/news-unexplained-red-rain-kerala |archive-url=https://web.archive.org/web/20100711014751/http://www.environmentalgraffiti.com/meteorology/news-unexplained-red-rain-kerala |url-status=dead |archive-date=2010-07-11 |title=The Unexplained Red Rain of Kerala |publisher=Environmentalgraffiti.com |access-date=2015-10-18 }}</ref> Samples of the red particles were also sent for analysis to his collaborators ] at the ] and ] at ]. Louis then incorrectly reported on 29 August 2010 in the non-peer reviewed online physics archive "arxiv.org" that they were able to have these cells "reproduce" when incubated at high pressure saturated steam at 121&nbsp;°C (]d) for up to two hours.<ref name=121oC/> Their conclusion is that these cells reproduced, without DNA, at temperatures higher than any known life form on earth is able to.<ref name=121oC/> They claimed that the cells, however, were unable to reproduce at temperatures similar to known organisms.

Regarding the "absence" of DNA, Louis admits he has no training in biology,<ref name='Dunning'/><ref> {{webarchive|url=https://web.archive.org/web/20180224113806/http://www.jewworldorder.org/fluorescence-mystery-in-red-rain-cells-of-kerala-india/ |date=24 February 2018 }} (2009) From Earthfiles Archive 2009 by Linda Moulton Howe.</ref> and has not reported the use of any standard microbiology ] to culture and induce ] and growth of the spores, basing his claim of "biological growth" on light absorption measurements following aggregation by ],<ref name=L&K2003b/> an inert physical observation. Both his collaborators, Wickramasinghe<ref name=astro>{{cite web | url=http://cardiffcentreforastrobiology.com/redrain.htm | archive-url=https://web.archive.org/web/20130729154051/http://cardiffcentreforastrobiology.com/redrain.htm | url-status=dead | archive-date=29 July 2013 | title=Cardiff Centre of Astrobiology: Analysis of Red Rain of Kerala | publisher=University of Cardiff | access-date=24 June 2008 }}</ref> and ]<ref name="David Darling's Newsletter #39"/> independently extracted and confirmed the presence of DNA from the spores. The absence of DNA was key to Louis and Kumar's hypothesis that the cells were of extraterrestrial origins.<ref name=L&K2003a/>

Louis' only reported attempt to stain the spores' DNA was by the use of ], which is generally used to stain bacterial endospores, not algal spores,<ref>{{cite web|url=http://www.microbelibrary.org/ASMOnly/details.asp?id=1610&Lang |title=Spore Stain Tutorial |access-date=31 August 2009 |last=Mayberry |first=William |date=7 April 2004|publisher=American Society for Microbiology |archive-url = https://web.archive.org/web/20070823083501/http://www.microbelibrary.org/ASMOnly/details.asp?id=1610&Lang |archive-date = 23 August 2007}}</ref> whose primary function of their cell wall and their impermeability is to ensure its own survival through periods of environmental stress. They are therefore resistant to ] and ], ], ], temperature, ] and chemical ]. Visualizing 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. The spores' DNA is tightly packed, encapsulated and desiccated, therefore, the spores must first be cultured in suitable ] and temperature to first induce ], then ] followed by ] before staining the DNA.<ref name='Dunning'/>

Other researchers have noted recurring instances of red rainfalls in 1818, 1846, 1872, 1880, 1896, and 1950<ref name='Dunning'/> and several times since then. Most recently, coloured rainfall occurred over Kerala during the summers of 2001, 2006, 2007, 2008,<ref name=Homepage>{{cite web |first=Godfrey |last=Louis |url=https://sites.google.com/site/godfreylouis/ |title=Home Page of Dr. Godfrey Louis |via=Google Sites |date=2008-10-06 |access-date=2015-10-18 |url-status=live |archive-url=https://web.archive.org/web/20160219195812/https://sites.google.com/site/godfreylouis/ |archive-date=19 February 2016}}</ref> and 2012; since 2001, the botanists have found the same ''Trentepohlia'' spores every time.<ref name='Dunning'/> This supports the notion that the red rain is a seasonal local environmental feature caused by ] spores.<ref name='Dunning'/><ref>{{cite web |url=http://theextinctionprotocol.wordpress.com/2012/07/14/myserious-blood-rain-again1-falls-from-skies-over-kerala-india/ |title=Mysterious blood rain falls again from skies over Kerala, India |publisher=Theextinctionprotocol.wordpress.com |date=2012-07-14 |access-date=2015-10-18 |url-status=live |archive-url=https://web.archive.org/web/20160115021906/https://theextinctionprotocol.wordpress.com/2012/07/14/myserious-blood-rain-again1-falls-from-skies-over-kerala-india/ |archive-date=15 January 2016}}</ref><ref>{{Cite web |date=2007-08-21 |title=Red rain again in Kerala? |url=https://www.hindustantimes.com/india/red-rain-again-in-kerala/story-Mtpg5x02ahowjBHbGXb01O.html |website=Hindustan Times}}</ref><ref>{{cite web |url=http://www.earthfiles.com/news.php?ID=1992&category=Environment |title=Fluorescence Mystery in Red Rain Cells of Kerala, India |date=6 July 2012 |publisher=Earthfiles.com |access-date=2015-10-18}}</ref><ref>{{cite web |url=http://globalrumblings.blogspot.com/2012/07/mysterious-bloody-rain.html |title=Panics Residents in Kerala, India Again |publisher=Globalrumblings.blogspot.com |date=2012-07-15 |access-date=2015-10-18 |url-status=live |archive-url=https://web.archive.org/web/20160115021906/http://globalrumblings.blogspot.com/2012/07/mysterious-bloody-rain.html |archive-date=15 January 2016}}</ref>

==In popular culture==
* The ] film '']'' was loosely based on the red rain in Kerala story. It was directed by Rahul Sadasivan and released in India on 6 December 2013.<ref name='film'>{{cite news | title = Red Rain film | date = October 2013 | url = http://entertainment.oneindia.in/malayalam/movies/red-rain.html | work = One India Entertainment | access-date = 2014-01-02 | url-status = live | archive-url = https://web.archive.org/web/20130909140314/http://entertainment.oneindia.in/malayalam/movies/red-rain.html | archive-date = 9 September 2013}}</ref>

==See also==
* {{annotated link|2015 Kerala meteorite}}
* {{annotated link|Panspermia}}
* {{annotated link|Yellow rain}}

==References==
{{Reflist}}


==External links== ==External links==
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*http://www.world-science.net/exclusives/060104_specksfrm1.htm World Science article
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*http://observer.guardian.co.uk/world/story/0,,1723913,00.html Article in ]
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*http://www.newscientist.com/channel/life/evolution/mg18925411.100 Article in ]
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Latest revision as of 13:51, 2 November 2024

Episodes of rain containing vast amounts of red algal spores in India For other uses, see Red Rain.

Rain water sample (left) and after the particles settled (right). Dried sediment (centre)

The Kerala red rain phenomenon was a blood rain event that occurred in Wayanad district of southern Indian state Kerala on Monday, 15 July 1957 and the colour subsequently turned yellow and also 25 July to 23 September 2001, when heavy downpours of red-coloured rain fell sporadically in Kerala, staining clothes pink. Yellow, green and black rain was also reported. Coloured rain was also reported in Kerala in 1896 and several times since, most recently in June 2012, and from 15 November 2012 to 27 December 2012 in eastern and north-central provinces of Sri Lanka.

Following a light-microscopy examination in 2001, it was initially thought that the rains were coloured by fallout from a hypothetical meteor burst, but a study commissioned by the Government of India concluded that the rains had been coloured by airborne spores from a locally prolific terrestrial green algae from the genus Trentepohlia.

Occurrence

Kottayam district in Kerala, which experienced the most red rainfall

The coloured rain of Kerala began falling on 25 July 2001, in the districts of Kottayam and Idukki in the southern part of the state. Yellow, green, and black rain was also reported. Many more occurrences of the red rain were reported over the following ten days, and then with diminishing frequency until late September. According to locals, the first coloured rain was preceded by a loud thunderclap and flash of light, and followed by groves of trees shedding shrivelled grey "burnt" leaves. Shriveled leaves and the disappearance and sudden formation of wells were also reported around the same time in the area. It typically fell over small areas, no more than a few square kilometres in size, and was sometimes so localised that normal rain could be falling just a few meters away from the red rain. Red rainfalls typically lasted less than 20 minutes. Each millilitre of rain water contained about 9 million red particles. Extrapolating these figures to the total amount of red rain estimated to have fallen, it was estimated that 50,000 kilograms (110,000 lb) of red particles had fallen on Kerala.

Description of the particles

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

Chemical composition

Elemental analysis
Analysis by the CESS
(%)
Analysis by Louis & Kumar (%)
Al 1.0 0.41
Ca 2.52
C 51.00 49.53
Cl 0.12
H 4.43
Fe 0.61 0.97
Mg 1.48
N 1.84
O 45.42
K 0.26
P 0.08
Si 7.50 2.85
Na 0.49 0.69
Photomicrograph of particles from red rain sample

Some water samples were taken to the Centre for Earth Science Studies (CESS) in India, where they separated the suspended particles by filtration. The pH of the water was found to be around 7 (neutral). The electrical conductivity of the rainwater showed the absence of any dissolved salts. Sediment (red particles plus debris) was collected and analysed 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. The CESS analysis also showed significant amounts of heavy metals, including nickel (43 ppm), manganese (59 ppm), titanium (321 ppm), chromium (67ppm) and copper (55 ppm).

Physicists Godfrey Louis and Santhosh Kumar of the Mahatma Gandhi University, Kerala, 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. A CHN analyser showed content of 43.03% carbon, 4.43% hydrogen, and 1.84% nitrogen.

Tom Brenna in the Division of Nutritional Sciences at Cornell University conducted carbon and nitrogen isotope analyses using a scanning electron microscope with X-ray micro-analysis, an elemental analyser, 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 analysed and seven were identified (in order of concentration): phenylalanine, glutamic acid/glutamine, serine, aspartic acid, threonine, and arginine. The results were consistent with a marine origin or a terrestrial plant that uses a C4 photosynthetic pathway.

Government report

A single spore viewed with a transmission electron microscope, purportedly showing a detached inner capsule.

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 (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, 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 Botanical 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 cultures were observed under a microscope.

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

The colour 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 area, when cultured in an algal growth 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

Trentepohlia on Cryptomeria japonica bark

The site was again visited on 16 August 2001 and it was found that almost all the trees, rocks and even lamp posts in the region were covered with Trentepohlia estimated to be in sufficient amounts to generate the quantity of spores seen in the rainwater. 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 Changanassery area. 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 cyanobacterium.

The report also stated that there was no meteoric, volcanic or desert dust origin present in the rainwater and that its colour was not due to any dissolved gases or pollutants. 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. 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 colour in the rainfall has been identified, finding the answers to these questions is a challenge." Attempting to explain the unusual spore proliferation and dispersal, researcher Ian Goddard proposed several local atmospheric models.

Parts of the CESS/TBGRI report were supported by Milton Wainwright at the University of Sheffield, who, together with Chandra Wickramasinghe, has studied stratospheric spores. In March 2006 Wainwright said the particles were similar in appearance to spores of a rust fungus, later saying that he had confirmed the presence of DNA, and reported their similarity to algal spores, and found no evidence to suggest that the rain contained dust, sand, fat globules, or blood. In November 2012, Rajkumar Gangappa and Stuart Hogg from the University of Glamorgan, UK, confirmed that the red rain cells from Kerala contain DNA.

In February 2015, a team of scientists from India and Austria, also supported the identification of the algal spores as Trentepohlia annulata, however, they speculate that the spores from the 2011 incident were carried by winds from Europe to the Indian subcontinent.

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. Coloured rain is by no means rare, and can often be explained by the airborne transport of rain dust from deserts or other dry regions which have been washed down by rain. "Red Rains" have been frequently described in southern Europe, with increasing reports in recent years. One such case occurred in England in 1903, when dust was carried from the Sahara and fell with rain in February of that year.

At first, the red rain in Kerala was attributed to the same effect, with dust from the deserts of Arabia initially the suspect. LIDAR observations had detected a cloud of dust in the atmosphere near Kerala in the days preceding the outbreak of the red rain. 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 coloured rain and the "burnt" leaves. The volcano was erupting in June and July 2001 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 sometimes flows from east to west at about 10° N, 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.

A study has been published showing a correlation between historic reports of coloured rains and of meteors; the author of the paper, Patrick McCafferty, stated that sixty of these colored rain events, or 36%, were linked to meteoritic or cometary activity, though not always strongly. Sometimes the fall of red rain seems to have occurred after an air-burst, 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.

Panspermia 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" in the 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 by 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. 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" 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 metabolise 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" which reiterated their arguments 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. The team also observed the cells using phase contrast fluorescence microscopy, and they concluded that: "The fluorescence behaviour of the red cells is shown to be in remarkable correspondence with the extended red emission observed in the Red Rectangle Nebula and other galactic and extragalactic dust clouds, suggesting, though not proving an extraterrestrial origin." One of their conclusions was that if the red rain particles are biological cells and are of cometary origin, then this phenomenon can be a case of cometary panspermia.

In August 2008 Louis and Kumar again presented their case in an astrobiology conference. The abstract for their 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 °C (572 °F). They can also be cultured in diverse unconventional chemical substrates. The molecular composition of these cells is yet to be identified.

In September 2010 a similar paper was presented at a conference in California, US.

Cosmic ancestry

Researcher Chandra Wickramasinghe used Louis and Kumar's "extraterrestrial origin" claim to further support his panspermia hypothesis called cosmic ancestry. This hypothesis postulates that life is neither the product of supernatural creation, nor is it spontaneously generated through abiogenesis, but that it has always existed in the universe. Cosmic ancestry speculates that higher life forms, including intelligent life, descend ultimately from pre-existing life which was at least as advanced as the descendants.

Criticism

Louis and Kumar made their first publication of their finding on a web site in 2003, and have presented papers at conferences and in astrophysics magazines a number of times since. The controversial conclusion of Louis et al. is the only hypothesis suggesting that these organisms are of extraterrestrial origin. Such reports have been popular in the media, with major news agencies like CNN repeating the panspermia theory without critique.

The hypothesis' authors – G. Louis and Kumar – did not explain how debris from a meteor could have continued to fall on the same area over a period of two months, despite the changes in climatic conditions and wind pattern spanning over two months. Samples of the red particles were also sent for analysis to his collaborators Milton Wainwright at the University of Sheffield and Chandra Wickramasinghe at Cardiff University. Louis then incorrectly reported on 29 August 2010 in the non-peer reviewed online physics archive "arxiv.org" that they were able to have these cells "reproduce" when incubated at high pressure saturated steam at 121 °C (autoclaved) for up to two hours. Their conclusion is that these cells reproduced, without DNA, at temperatures higher than any known life form on earth is able to. They claimed that the cells, however, were unable to reproduce at temperatures similar to known organisms.

Regarding the "absence" of DNA, Louis admits he has no training in biology, and 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 light absorption measurements following aggregation by supercritical fluids, an inert physical observation. Both his collaborators, Wickramasinghe and Milton Wainwright independently extracted and confirmed the presence of DNA from the spores. The absence of DNA was key to Louis and Kumar's hypothesis that the cells were of extraterrestrial origins.

Louis' only reported attempt to stain the spores' DNA was by the use of malachite green, which is generally used to stain bacterial endospores, not algal spores, whose primary function of their cell wall and their 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. Visualizing 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. The spores' DNA is tightly packed, encapsulated and desiccated, therefore, the spores must first be cultured in suitable growth medium and temperature to first induce germination, then cell growth followed by reproduction before staining the DNA.

Other researchers have noted recurring instances of red rainfalls in 1818, 1846, 1872, 1880, 1896, and 1950 and several times since then. Most recently, coloured rainfall occurred over Kerala during the summers of 2001, 2006, 2007, 2008, and 2012; since 2001, the botanists have found the same Trentepohlia spores every time. This supports the notion that the red rain is a seasonal local environmental feature caused by algal spores.

In popular culture

  • The science fiction film Red Rain was loosely based on the red rain in Kerala story. It was directed by Rahul Sadasivan and released in India on 6 December 2013.

See also

  • 2015 Kerala meteorite – Meteor air burst over Kerala, IndiaPages displaying short descriptions of redirect targets
  • Panspermia – Hypothesis on the interstellar spreading of primordial life
  • Yellow rain – Purported chemical weapon

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