Ridley Scott has been talking about his plans for Prometheus sequel Alien: Paradise Lost, stating that it will be followed by another sequel, which will then “back into Alien 1" and answer the biggest question of them all, reports IGN.
First up, The Martian helmer expressed his regret at not taking charge of the sequels first time around, saying “I’m trying to keep this for myself. I let the other one [Alien] get away from me – I shouldn’t have… I’m trying to re-resurrect the beast and let if off the hook for a while because I’m coming back into the back-end of Alien 1. I’m gradually getting to Alien 1."

And it sounds like the films will answer questions that the franchise original asked back in 1979…
“Prometheus 2 will start getting shot in February and I’ve already begun now so I know what the script is. Then there will be another one after that and then maybe we’ll back into Alien 1, as to why? Who would make such a dreadful thing?”
For official quotes by Ridley Scott and the cast and writers of Prometheus that help explain some of the mysteries raised in the first film, take a look at the Meaning of Prometheus and Connections With Alien sections in the IGN Prometheus Wiki.

Alien: Paradise Lost is scheduled to hit screens May 2017, while The Martian is still in cinemas.