When heavy rains hit Kerala, a coastal state in southern India, in 2001, people were concerned about a strange phenomenon. The "rain" was red, and it stained their clothes. The colored droplets fell on and off over a two-month period, in very localized spots, diminishing over time. While sometimes the rain took on yellow and green hues, the main color was blood-red [source: Darling].
Initially, some suspected this unusual activity was caused by an exploded meteor, as some early eyewitnesses reported hearing a boom and seeing a flash of light shortly before the red rain first fell. The next thought was that the cause was scarlet sand blown in from Arabia, which mixed with the rains. But studies showed that the red particles extracted from the water were not grains of sand. No, the ruby flecks appeared to contain cells of a biologic origin. In fact, they looked quite like those of bugs [sources: The Living Moon, MIT Technology Review].
One duo studying the particles — Godfrey Louis and his research assistant, A. Santhosh Kumara, of Kerala's Mahatma Gandhi University — came up with a unique theory. The red rain, they said, got its color from extraterrestrial organisms. Taking the booming noise into consideration, Louis posited a comet disintegrated, its pieces seeding clouds, which then encapsulated them into raindrops that fell to earth. His results were published in 2006 in the peer-reviewed journal Astrophysics and Space [source: MIT Technology Review]. The Indian government's conclusion? Airborne algal spores from local trees [source: Darling].
Louis continued studying the red cells with an international team of researchers. The group reported that while the cells are inert at room temperature, they reproduce when heated to 250 degrees Fahrenheit (121 degrees Celsius), something highly unusual. DNA also has been found in the cells, but it can't be extracted [sources: The Living Moon, Darling].
No one can explain the phenomenon with any certainty. (And no meteoric dust was found in the samples.) However, those who believe in the extraterrestrial theory say it's evidence of panspermia, a theory that life can be seeded on various worlds from space. In 2012, red rain once again fell from the skies of Kerala [source: Ians].