A maybe SPOILER WARNING is needed for this, but that's up to you, I don't think revealing who an actor is playing can be considered a spoiler – if the studio wanted the character a secret, better not reveal the actor at all. But I understand everyone's spoiler-tolerance levels are different.
So if you want to know who Jessica Chastain is playing in Interstellar, keep scrolling down for the tweet from The Wrap reporter Jeff Sneider. If you don't want to know, stop right here…. but risk losing out on all the great discussion that will happen between people who do choose to know. I know. It's a conundrum.
But seriously, stop reading now if you don't want to know.