With only about four weeks left before Iron Man 3 begins shooting, some casting additions are still being made.  Not only has the great Sir Ben Kingsley come on board in a villainous capacity, but the charismatic Guy Pearce is reportedly adding his talent to the Marvel movie.  Now, the latest reports have Jessica Chastain back on track to join the threequel.  Her role is purportedly that of a sexy scientist who rivals Tony Stark (Robert Downey Jr.) in intelligence.  Chastain was previously thought to be in the mix for the role before scheduling issues complicated matters.  With her film The Disappearance of Eleanor Rigby: Hers pushed back, it looks like Chastain will be joining Gwyneth Paltrow, Don Cheadle and possibly Scarlett Johansson for Iron Man 3. Hit the jump for more. Deadline is jessica-chastain-iron-man-3reporting that Chastain is once again the frontrunner for the "sexy scientist" role in Iron Man 3. The studio had previously entered into meetings with Diane Kruger, Isla Fisher and Gemma Arterton for the role, but apparently wants to advance Chastain to the top of the list.  While few other character or plot details have surfaced with this announcement, there has been some speculation as to the storyline of Iron Man 3 by writer/director, Shane Black (Kiss Kiss, Bang Bang) and co-writer, Drew Pearce (No Heroics).  If potential spoilers don't bother you, feel free to read up on the possible plot points here.  Spoiler-phobes should also stop reading this article now if they want to stay as ignorant as possible about the movie. While I won't go into detail about the speculation (as to avoid spoilers), it's possible that the "sexy scientist" in question is Maya Hansen, a relatively new character in the comics that is introduced as having a backstory with Stark and also involves him in a bit of trouble once he becomes Iron Man.  More details on her involvement with Stark can be found in the comic summary here.