Like something out of a biblical tale or Slayer song, parts of India and Sri Lanka have been experiencing occasional rainfalls colored mostly red and recurring over several years. Sometimes the coloring is so deep the drops look like blood and can stain clothing.

Since the first modern fall in 2001, several scientists have followed their curiosity to find out what exactly is causing the red rain. Many felt they have come to a conclusion but for every proposed answer more questions seem to emerge.

■ Dust
Initially people assumed the red coloring was caused by dust from a desert, volcano or meteor. When samples of the red water were collected in test tubes, whatever was causing the coloration appeared to settle to the bottom. However, further tests showed that although it contained traces of various metals, the substance was organic.

■ Lichen
The Center for Earth Science Studies (CESS) is located in Kerala, India, where the 2001 red rain incident occurred, and the Tropical Botanic Garden & Research Centre (TBGRI) examined the red substance further after ruling out an inorganic substance.

Checking with a microscope the TBGRI determined the substance was largely made up of spores from some type of algae or fungus. They took the spores and grew them to determine more clearly what organism they belong to. After cultivating them in a petri dish they were found to be of the Trentepohlia family of algae.

Image: Sampath, Abraham, Kumar, and Mohanan

Trentepohlia exists along with fungi and cyanobacteria to make up a particular lichen with a somewhat orange tinge, which is widely found in the Kerala area. The CESS and TBGRI concluded that due to the similar color and prevalence of the lichen, an especially large release of spores is what caused the red rainfall.

■ Loose ends
In the conclusion of their report, the CESS also acknowledges unexplained events surrounding the 2001 red rain. First, if the red coloration was caused by algae spores, then what caused them to rise high enough and in such a large quantity to change the color of the rain for about 10 days, and why doesn’t this happen more often?

Also, prior to the red rain several residents reported hearing a loud sound similar but not quite like thunder and unusual lights. The 2001 red rain occurred during monsoon season when thunder storms are rare. These reports are what led many researchers to assume the red coloring was caused by the explosion of a meteor. Yet with a meteor cause ruled out, there’s still the question of what caused the lights and sounds.

■ Alien Lichen?
The unanswered questions in the CESS report and studies by others provided the groundwork for some subscribers to panspermia theory. Panspermia is the idea that life on Earth (like any other life bearing planet) was brought from another celestial body via comets. Leading the way in research connecting the red rain with a panspermia event are Godfrey Louis and A. Santhosh Kumar of Mahatma Ghandi University in Kerala.

The two made a compelling case that what occurred prior to the 2001 red rain event was a sonic boom created by a meteor based on witness testimony and the pattern of rainfall. They theorize that the red rain’s cells were carried from that rock and dispersed into the atmosphere where it precipitated in the rain. They also conducted a series of physical and chemical tests to show that the cells could withstand the conditions of space travel and entrance through the Earth’s atmosphere successfully.

Image: Godfrey and Kumar

However, Louis and Kumar have met controversy with suggestions that the red rain cells have no DNA, but can reproduce even under extreme temperatures – something no life on Earth is capable of. This finding has been refuted by other researchers who claim to have found DNA. The panspermia theory also runs into trouble with the considerable volume of cells dispersed as well as the fact that red rain has fallen at other times in the same general vicinity over the past decade.

Considering the two major theories it would seem more rational to back the idea of a sudden massive release of Earth-based algae spores into the atmosphere. However, both theories aren’t without their holes leaving this phenomenon open for discussion.

The most worrisome part of this red rain is perhaps summed up best by David Darling on his website: “If we find it so hard to establish definitively the nature and origin of such a massive biological fallout in our own planetary backyard, what chance do we have of identifying life remotely in much smaller quantities on Mars or other neighboring worlds?”

Source: Karapaia (Japanese), Arxiv, CESS, David Darling’s Newsletter (English)
Video: YouTube – Science Channel

▼ A Science Channel feature on red rain that appears to support Louis and Kumar’s theory