Since the beginning of human thinking, we have been curious about two questions: ‘Who are we?’ and ‘Where did we come from?’. According to scientists, life on Earth started approximately 3.8 billion years ago with the emergence of unicellular beings whereas multicellular beings evolved a billion years later. The life forms that we are familiar with today, appeared only about 570 million years ago. But how did life begin on Earth? Did it originate over here or did it come from the outside? These are some of the questions that astrobiology strives to answer. Astrobiology is an emerging science but its concept has existed since the beginning. It doesn’t define “life” but studies its origin, evolution and distribution in the universe. Astrobiologists try to explain the origin of life with the help of different theories. According to biologists and researchers, an object which is capable of growth, reproduction and the utilization of energy, plus has an ordered structure, responds to environment and adapts to evolutionary changes is defined as a living thing.
There are two theories that astrobiologists emphasize on, Panspermia and Darwinism – the latter one is considered to be more reliable. Panspermia theory states that some largely organic (containing carbon) interstellar dust entered Earth’s atmosphere and brought about the changes necessary for macro-evolution. Charles Darwin, an English naturalist and biologist, stated that all species of organisms have arisen and developed through natural selection of small inherited variations that increased an individual’s ability to compete, survive and reproduce (Darwinism).
The Viking project (Viking 1 & 2) was the first American mission to land safely on Mars to search for bio-signatures in Martian soil. However, no conclusive evidence was found that life existed there. In 1996, some scientists claimed that they had found microscopic fossilized bacteria on the meteorite ALH8400, however, later, it was suggested that such structures could have been formed by the coating used for electron microscopy. Numerous other incidents have been claimed to be evidence for the presence of extra-terrestrial life including the Wow! Signal (1977), Red Rain in Kerala (2001) and cells found in the stratosphere after a meteor shower (2013). Nonetheless, not a single authentic piece of evidence exists that could confirm the presence of life beyond Earth.
Climate change and population explosion are warning humans to look for the possibility of life beyond Earth. Stephen Hawking, a British physicist and cosmologist, claimed in his recent interview that global warming is on the verge of becoming an irreversible phenomenon and that humans should find an alternative habitat in order to avoid extinction.
The search of life beyond Earth has intensified in the last two years because of the discovery of exoplanets (planets outside our solar system that orbit a star). Today’s technology has enabled us to send probes far beyond our own solar system. As of November 2017, Kepler mission has discovered 4496 exoplanet candidates and 2337 confirmed exoplanets. Giordano Bruno, an Italian mathematician and cosmological theorist said, “This space we declare to be infinite, since neither reason, convenience, possibility, sense-perception nor nature assign to it a limit. In it are an infinity of worlds of the same kind as our own’’.
The discovery of habitable exoplanets and development of biosynthetic and environmental technology has turned ‘terraforming’ into a reality. Terraforming is the hypothetical process of deliberately modifying the atmosphere, temperature, surface topography or ecology of a planet to be similar to the environment of Earth to make it habitable.
Some sort of a microbial system is necessary in order to colonize a planet. In 1956, astrobiologists discovered Deinococcus radiodurans, an extremophilic bacterium (bacteria which can survive in extreme conditions) that is radiation-resistant. It can survive cold, vacuum, dehydration and acid and is therefore known as a poly-extremophile. It has been listed as the world’s toughest bacterium in The Guinness Book of World Records Natrialba magadii is an organism (belonging to the domain of Archaea) which survives at high pH. Both of these organisms are considered to be able to survive in space.
Terraforming Mars or another planet is now a possibility in the near future and if it succeeds, it will revolutionize space exploration. On the other hand, some people question the need of terraforming other planets, and argue that the money should be spent on improving the conditions on Earth and bringing back the green pastures and clear blue skies.