Researchers now believe that aliens are probably extinct which is why we have not spotted one yet. This group of astrobiologists says that if life exists on other planets, it would have been brief due to extreme heating or cooling that made living on their planets impossible.

Lead author Aditya Chopra said that the universe is filled with habitable planets so the possibility of aliens inhabiting these places is very likely. In the study, published in the journal Astrobiology, she adds that early life rarely evolves immediately because it is fragile and most early planetary environments are unstable.

The scientists claim that Venus and Mars could have hosted life billions of years ago. However, because the planets failed to stabilise the rapidly changing environment, Venus became too hot and Mars became too cold according to associate professor from the ANU Planetary Science Institute and co-author, Charley Lineweaver.

These planets needed to evolve fast enough to regulate greenhouse gases and maintain stable surface temperatures. Lineweaver noted that life on Earth played a major role in stabilising the climate, allowing life to thrive.

In recent years, scientists claim that Earth-like planets are common than previously thought. Still, Lineweaver adds that that Earth may be one of those rare places where life was able to ensure its own survival and where one-celled bacteria evolved into complex species.

They also believe that gases such as hydrogen, oxygen, phosphorus and sulphur, which are all considered as basic ingredients for life, are abundant. Nevertheless, no concrete evidence have been discovered to prove that life really exists in these so-called habitable zones.

Many experts have also believed that aliens are perhaps too far away or too advanced for Earth’s technology to find them. But, if scientists can finally find evidence of bacteria that have once lived on other planets, it will help support this new theory.