Question

How many planets in the universe can support life?

Answer 1

Hint: This is a question of general physics and its answer depends on our meaning of what we consider a habitable planet. We know for planets to be inhabitable, they have to be a rocky planet or one could say an exo-planet. There is no scope of life on a planet which is completely made up of gases like Jupiter or Saturn, etc.

Complete step by step answer:
Now, to find an estimate to how many planets in the universe can support life, we will first need to observe the total number of galaxies in our universe. We will then estimate the total number of stars in these galaxies. Once this is done, we calculate the total number of planets and then divide them under two categories, one that supports life and one that doesn’t.
For any planet revolving a star in the universe, it must lie in the habitable zone of that star. Habitable zone of a star is defined as the region around the star which is neither too hot nor too cool. It is that ideal condition under which liquid water can exist on the planet as it is considered to be the basic requirement for a planetary system to support life.
The exact number of these planets that support life is a matter of debate but with the help of the data collected by telescopes all over the world under the Kepler Space Mission astronomers reported there could be around 40 billion Earth-like planets orbiting the habitable zones of their respective stars or even red dwarfs in Milky Way alone. And further using the Hubble’s telescope, astronomers have predicted that there are about 100 billion galaxies in our cosmos. This makes the total number of inhabitable planets in the order of around $10^{21}$.

Note: There are billions of planets out there that once used to support life but have now perished from the face of the universe or are unable to support life today, like the planet Mars in our solar system. Also, millions of new planets are created every day, some of which will finally take place in the habitable zone of their star and may support life one day.