# Could humans survive on other planets in the universe?

Feb 4, 2016

In my opinion : Yes .. But unfortunately we are not able to explore all the universe (limitations by actual technology).

#### Explanation:

At this moment, we didn't find another planet able to respect all the conditions for humans. This is a tricky problem.
Let's take our galaxy as example :

• First, you need to have a star similar to our sun, type G, and there are only 8% of the stars in our galaxy which this type !

N.B : if we assume that the Galaxy contains $200 \times {10}^{9}$ stars, then there would be 16 billion G type stars.

• You have to be in the habitable zone of the galaxy (region of a galaxy in which life is most likely to develop taking several factors like major risks : supernova,...).

Let us further assume that 10% of these stars are in the habitable zone of the galaxy, therefore remaining 1.6 billion stars.

• You need to have a planetary systems, but it seems the occurrence is quite common, so we can assume $\frac{1}{3}$ of these stars have planetary systems $\to$ 0.5 billion planetary systems in the habitable zone of the galaxy remain.

• The planet should be an Earth sized planet with a large satellite that stabilizes its rotational axis. If the percentage of G stars that have planetary systems and a planet of Earth size in its habitable zone is 0.1%, then there remain still $\text{500,000}$ objects.

• You also need some big planets in the planet system , like Jupiter for us, to attract most of the asteroids. Moreover, of the $\text{500,000}$ objects, we can assume only $\frac{1}{1000}$ contain a continuous habitable zone (no nearby supernova explosion, no catastrophic impacts,...) $\to$ still $500$ objects remain.

• Then there is the factor of age . It took about $3.5$ billion years for life to develop to higher forms. How many of these $500$ objects are old enough ?

If we take a crude value of $\frac{1}{10}$, then finally our very drastic approximation gives $50$ living civilizations in the galaxy !

And this is with pessimistic estimation considering only G-stars, maybe we can extend with K-stars ...

Conclusion : It's not a large number but definitely different from one and only for our galaxy .. So I am pretty sure it's possible !