Born in the Universe: The Panspermia Theory
Since 2004, NASA’s Cassini spacecraft has been orbiting Saturn to study the giant planet’s moons and rings using an array of complex instruments, one of them being a vacuum cleaner, designed to analyze dust particles. This instrument has now detected the faint but distinct signature of dust coming from beyond our solar system: 36 grains of interstellar dust rich in minerals such as magnesium silicates and oxides, as well as iron, that were left over from the death of a distant star.
It is a widely accepted hypothesis that current life on Earth descended from an RNA world, an episode of life on Earth during which RNA (ribonucleic acid) was the only genetic material. The 'panspermia' theory states that this wasn't a spontaneous process that just happened by luck, but that the building blocks and molecules necessary for life to develop are abundant all over the Universe and that 'seeds of life' can be propagated through space from one location to another by comets, asteroids, meteorites etc.
Recently, an experiment conducted by Cornelia Meinert, an associate scientist at the Université Nice Sophia Antipolis in France, demonstrated that the building blocks of RNA are indeed present in interstellar environments. By treating a mixture of water, methanol and ammonia very similar to a comet and hitting it with the same radiation that would have been given off by the Sun from millions of years ago, a huge diversity of molecules was created. The most sensational however was the discovery of ribose, which is the sugar that forms the backbone of RNA.
In another study last year, Karen Smith and her team at NASA's Goddard Astrobiology Laboratory analyzed eight different meteorites and found that they contained up to 600 parts-per-billion of vitamin B3. They also simulated interstellar conditions in the lab and suggested that the radiation powering various chemical reactions in cloud nebulae could have produced vitamin B3 on ice grains.
"Vitamin B3, also called nicotinic acid or niacin, is a precursor to NAD (nicotinamide adenine dinucleotide), which is essential to metabolism and likely very ancient in origin", according to Smith. "It is always difficult to put a value on the connection between meteorites and the origin of life; for example, earlier work has shown that vitamin B3 could have been produced non-biologically on ancient Earth, but it’s possible that an added source of vitamin B3 could have been helpful."
Although hard evidence remains to be found, the number of discoveries that support the panspermia theory is growing steadily. Last year, observations made by ESO with the ALMA radiotelescope in the Atacama desert in Chile revealed the presence of vast quantities of complex organic molecules around a very young star (MWC480), situated 455 light years away.
A type of single-celled algae called Nannochloropsis Oculatatiny appears to be able to survive a space trip without any trouble, as well as an eight-legged critter called “water bear,” that can suspend all biological activity in extreme environments and survive the vacuum of open space and solar radiation combined for at least 10 days. Scientists have also found that a certain strain of bacteria named Bacillus Safensis grows about 60% better on the ISS than on Earth, and recent research has yielded a number of microrganisms that could potentially withstand many of the same extreme conditions found on Mars and other distant planets.
According to Professor Avi Loeb, chair of the Department of Astronomy at the Harvard University, it is possible for life to be carried by rocks and other matter that is ejected from one planet, maybe after the impact of an asteroid, and land on another planet. This can happen if the two planets are in the same planetary system but also, with smaller likelihood, if they are in different systems.
He suggests that if life spreads via panspermia, it does it in a characteristic pattern that we could identify. His research shows that this pattern would be similar to the outbreak of an epidemic. He states that there is a biological similarity between panspermia and disease spread: Any species that evolves panspermia abilities would have enormous fitness advantages.
Many scientists believe that we will soon find traces of alien micro-organisms. This first fingerprints of life could be identified in the atmospheres of extra-solar planets through spectrographs on the next generation of telescopes, but they may also be found on planets and moons within our solar system. Such a find would of course immediately raise the question of how we can be shure that no contamination by terrestrial organisms has taken place. Just the same, the panspermia theory is a keystone in the search for extraterrestrial life for future generations.