boreal chasm
I got this screen shot yesterday right after getting Arcturus for the first time during this simulation run. As can be seen in the screen shot, I have Arcturus, since I can see it up close, but also note that it is not in the list of generators. Also, when I was in the tree view, Arcturus was not showing up as being available. So at the time that I took this screen shot, there was no way for me to do anything with Arcturus except view how pretty it was in the garden.
I should note that due to how I advanced through the simulation, I was able to get Arcturus before I got Polaris. I mention this because this story does have a happy ending. Once I did get Polaris, then Arcturus also showed up in the generator list and the tree view as well, and the game went on normally from there.
So this is probably more of a UI bug than anything else: some kind of condition that seems to assume/require availability for Polaris before letting the player do anything with Arcturus even though it is very possible to get Arcturus before getting Polaris.
