John Landgraft, the FX boss, told Variety:

Noah is deep in work on Season 1 of "Alien: Earth" right now. We're in post-production, and we are talking to him and watching cuts every week. We're pretty bullish on "Alien: Earth" and we've told him that assuming, as we hope, "Alien: Earth" is a returning television series, we want him to focus on on at least writing two seasons of it before returning to a possible sixth season of "Fargo."