Are we alone in the universe? If your answer is no, then how do you detect the existence of life in space? Astrobiology/exobiology is the science which looks for the presence of extra terrestrial life in the universe.
Astrobiology deals with the origin, evolution and distribution of life in the universe and to investigate the possibility of life in other world.
The major concept in astrobiology is the habitable zone. The theory explains that any planets can support the existence of life, if it fulfills two important criteria.
i. It must have a right mass to retain an atmosphere.
ii. It must have an orbit at just the right distance from its star (Sun) that it allows liquid water to exist. Thus, the distance need to be neither too hot or not too cold and is often referred as Goldilock Zone for life.
In our solar system ‘Earth’ is the only planet in the goldilock zone. Since, this zone varies at times as the star evolves, we know that Mars have also been habitable. The life on Mars are likely to be the creatures, we find in extreme environments on earth.
The organisms which live in extreme environmental conditions on earth are called extremophiles. Thus, within our own Solar System, there are many areas that are different from the Earth where it is probable to find the presence of life similar to extremophile bacteria.