IESB.net has received confirmation from actress Jennifer Morrison's management company that she has been cast in J.J. Abrams Star Trek, however, they would not reveal which character she will be playing.
The site speculates (although cannot prove) that she most likely would play a young civilian biologist by the name of Carol Marcus, the mother of Kirk's son, David Marcus.
Carol devoted her life to her research. In the early 2260's Carol became involved with a young Starfleet officer named James T. Kirk, and in 2261 she gave birth to their son, David Marcus. However, she felt that they had no basis for a lasting relationship, with Kirk traveling around the universe while she worked in a lab, so she asked that Kirk leave her alone to raise the boy.
In addition, the site has confirmed that Chris Hemsworth has been cast in the film as Kirk's father, George Samuel Kirk Sr.