If you jizz in space, will your jizz be propelled endlessly across the universe? Unless it gets caught up in a planet's gravity or a black hole (not your mom's)? Will the cold temperatures of space preserve your jizz, enabling any aliens who find it to create a new human race? Or will they eat it as a snack?
Will they like the taste of jizz so much that they will trace its trajectory back to earth? Will they take over the planet and harvest endless amounts of jizz? How will they harvest jizz? Will they use alien-created milking machines or will they just suck everyone's dick?