Clouds of alien life forms are sweeping through outer space and infecting planets with life it may not be as far-fetched as it sounds. The idea that life on Earth came from another planet has been around as a modern scientific theory since the 1960s when it was proposed by Fred Hoyle and Chandra Wickramasinghe. At the time they were ridiculed for their idea known as panspermia. But now, with growing evidence, it's back in vogue and even being studied by NASA. We meet the scientists on a mission to get to the bottom of the beginnings of life on Earth - from the team in Texas who are lovingly building a robotic submarine called DEPTHX to explore a moon of Jupiter, to Southern India where they are investigating a mysterious red rain which fell for two months in 2001. According to local scientist Godfrey Louis, the rain contains biological cells unlike any he had seen before � with no DNA and the ability to replicate at 300�C. Louis has come to the conclusion that the cells are extra-terrestrial in origin. Could all this really be proof that We are the aliens?

Panspermia is the hypothesis that the seeds of life are in the Universe, that they may have delivered life to Earth, and that they may deliver or have delivered life to other habitable bodies; also the process of such delivery. Exogenesis is a related, but less radical, hypothesis that simply proposes that life did not originate on Earth, but was transferred to Earth from elsewhere in the Universe, with no prediction about how widespread life is. The term "panspermia" is more well-known, however, and tends to be used in reference to what would properly be called exogenesis, too.

The first known mention of the idea was in the writings of the 5th century BCE Greek philosopher Anaxagoras, but panspermia theory was dormant until the nineteenth century when it was revived in modern form by several scientists, including Hermann von Helmholtz in 1879 and, somewhat later, by Svante Arrhenius in 1903. Panspermia can be said to be either interstellar (between star systems) or interplanetary (between planets in the same solar system). There is as yet no compelling evidence to support or contradict it, although the majority view holds that panspermia especially in its interstellar form is unlikely given the challenges of survival and transport in space.

Sir Fred Hoyle (1915 - 2001) and Chandra Wickramasinghe (born 1939) were important proponents of the hypothesis who further contended that lifeforms continue to enter the Earth's atmosphere, and may be responsible for epidemic outbreaks, new diseases, and the genetic novelty necessary for macroevolution. This extension has also been adopted by proponents of Cosmic ancestry.

Panspermia per se does not remove the need for life to originate somewhere, but does extend the time frame and environments available. Similarly, it does not necessarily suggest that life originated only once and subsequently spread through the entire Universe, but instead that once started it may be able to spread to other environments suitable for replication. (In the strongest version of panspermia, life never originated, but always existed this axiom would require amending the big bang theory.) The mechanisms proposed for interstellar panspermia are hypothetical and currently unproven. Interplanetary transfer of material is well documented, as evidenced by meteorites of Martian origin found on Earth. However, claims that these carry evidence of extraterrestrial lifeforms let alone viable dormant lifeforms have either been proven unfounded as a result of terrestrial contamination, misinterpretation, or hoaxing; or are currently hotly disputed. Interestingly, space probes may also be a viable transport mechanism for interplanetary panspermia in our solar system (or even beyond) especially given the claim (now no longer sustainable) that terrestrial bacteria were supposed to have survived in a dormant state on the Moon. Since then, however, NASA has implemented strict abiotic procedures to avoid planetary contamination.

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