We knew an expansion was coming as it was confirmed some time ago, but now Wube Software have revealed much more about what's now called Factorio: Space Age.
This expansion will continue your building after you launch into space at the end of a game in Factorio. You'll get to discover new worlds with challenges, exploit their resources and manage your fleet of interplanetary space platforms they say.
With this expansion though, instead of sending up one rocket, you'll be sending many! As these will provide resources in orbit for you to use to build big space platforms. However, since you're doing it multiple times, rockets will be a bit cheaper to produce. There will be 4 extra planets, each with a unique theme, resources, challenges and gameplay mechanics and some have different military targets too.
There's still the free 2.0 update coming which will benefit all players, as technically the expansion will act like a mod on top of their updated base game. Some things you'll get in the update includes the ability to control train systems better, better blueprint building, better flying robot behaviour and more to be revealed.
It's not due a while though, they say at least another year until it's ready. However, they will now be talking about the expansion regularly to go over more details of it.
The blog post also touches on how it's similar to the Space Exploration mod. There's a good reason for that, as Earendel who made the mod is part of Wube Software and has also been working on the expansion. They say that Space Age though is designed for everyone, and required game engine changes for what they wanted to do with it.