When the alien creature first enters Porky's campsite the camp fire has no smoke coming from it. Later when the alien is cutting around the camp, the camp fire has smoke coming from it. Later when the alien places its hand on Sylvester in outer space the camp fire has no smoke. Later when the items from Porky's camp float down onto the alien planet, the camp fire has smoke again.
When Porky and Sylvester (and the campsite) floated away from the saucer, they floated softly down on some other planet in the Solar System. Whatever planet it is, the gravitational pull would have been enough to cause a hard landing - probably fatal.
Since Porky, Sylvester, and the rest of the campsite landed on another planet in the Solar System, no planet (other than Earth) has enough oxygen to support combustion, thus the car would never have started.
Stars are shown inside the crescent of the moon.
Since the saucer did not have any way of containing any atmosphere, as soon as the saucer left the Earth's atmosphere, Porky and Sylvester would have died.