‘Life’ is one of the most mysterious words. The planet Earth is the only known place where life exists. Astronomers are too keen to know about the existence of life on other places than Earth. Lots of new techniques and experiments are done daily to observe the evidence of life outside the planet Earth. Let us look at some basic requirements for the existence of life on any planet or moon.
The two fundamental requirements are moderate temperature range and source of energy. Habitable temperature range is necessary for most of the biochemical reactions and also for the stability of molecules. Life cannot exist with too high or too low temperature.
The source of energy is fundamental need of life; all the activities of life are powered by energy. The source of energy may include host star, planet’s internal energy or some radioactive decay. In the case of Earth, the main source of energy is the Sun. Plants are the main absorber of energy from the Sun and then they transfer it to other organisms. In the case of moons, the planet may play the role of energy sources like the planet Jupiter and the planet Saturn.
Energy on moons may also be generated from tidal forces applies by a planet like Io which is the moon of Jupiter, it has volcanoes on its surface due to tidal forces of the planet Jupiter that provide very high temperature and energy.
Now there are other requirements also which are necessary. The Green House Effect is somehow related to the maintenance of constant temperature in day and night. Green House Effect may increase the temperature by a large amount like nearly 500 degree Celsius on the planet Venus.
Atmosphere is required to protect life from meteorite hits and some radiations like Ultra Violet Radiations in the case of the ozone layer. The size of meteors reduces up to zero and burn out completely when they travel through the atmosphere. The atmosphere of Earth also protects us from the cosmic radiations and neutron radiations.
Magnetosphere is also necessary to protect life from Solar Radiations and also planetary radiations in the case of moons. The planet Jupiter and Saturn emit radiations of heavy particles which have the ability to degrade atmosphere of moons and also destroy life. Ganymede is the only moon of Solar System which has its own magnetic field.
The life on Earth is mainly centered on water and some elements like C, N, O, and H etc. But it is not necessary that life needs water to exist. Water is good solvent and provides the medium for a large number of reactions but other chemicals may also play the same role in some other planet to support life.Carbon forms
Carbon forms large number of molecules that enables life to exist on Earth. Nitrogen helps in producing amino acids and DNA. But life may use different molecular structures which can be totally different from the case of Earth.
Although water, carbon and oxygen provide easy evidences for existence of life but universe is not very small it might be possible that somewhere in the universe life is growing in some unknown environment which cannot be imagined easily just by looking at life on Earth.