By saving their world, they erased their future

Valérian et Laureline is a science fiction comic book series created in 1967 by Pierre Christin and Jean-Claude Mézières. The two heroes travel through time to protect their empire without altering the past, but they end up helping to prevent the nuclear explosion of 1986. By succeeding in this temporal manipulation, they cause the future of their own planet Galaxity to disappear and must set out in search of it.