Most of them are fiction.

There is no evidence to prove the existence of alien life.

There is no evidence that aliens exist.

Other planets don't have water, air, sunshine and suitable temperature to support intelligent life.

On another planet, there is no water, air, sunlight and suitable temperature to support the existence of intelligent life on other planets.

Before launching a satellite to explore Mars, people did not guess the existence of Martians, but after satellite exploration, they realized that there was no alien life on Mars.

Before we sent satellites to Mars, people speculated that there were Martians there. After all, there were no aliens on Mars.

There is no scientific basis for the existence of aliens to be established only in sparsely populated places.

If aliens exist, they should not live in places where few people live. This statement has no scientific basis.