The story of a little alien stranded on an unfamiliar planet struck a chord with some big stars.

“Home,” DreamWorks Animation's latest foray into 3D CG-animated filmmaking, centers on Oh, an initially not-so-capable member of the Boov, an alien empire looking to take over Earth and use it as its new home – and a hiding place from even more insidious enemy race. Banished after accidentally tipping off the Boov's rivals to their new locale, Oh (voiced by Jim Parsons) finds himself in an unlikely alliance with a resourceful teen named Tip (pop star Rihanna), who's looking for her mother after being separated during the Boov invasion. Both are hunted by the so-clueless-he's-actually dangerous Boov leader Captain Smek (Steve Martin).

What lured such as all-star cast – which also includes Jennifer Lopez as Top's mom – to the project? Parsons, Rihanna and Martin joined director Tim Johnson (“Antz,” “Over the Hedge”) at a recent press conference to reveal what it was that made them say "Oh!"

Rihanna: Neither [Parsons nor I] had ever done an animated film, and the story just spoke to me. It was so real, and I found so many parallels in it. I felt like I identified with Tip. She’s essentially a role model, and for me it was very strange reading a character that you could look up to. I was very excited.

I’d never done an animated film before. I did “Battleship,” but this was different. You learn so much when the camera is not there — especially for me, being from Barbados, I have an accent, so learning to speak American you realize that there’s 20 different types of American. There’s all these different types of accents, which I didn’t know. I was learning all over again, not just about accents but also how to act with my voice.

Jim Parsons: Even before I knew what the story was I was very excited about the idea because I wanted a chance to do an animated film. And then once we talked about it I just like the little character that I was playing so much — even the way he looked. I held up a photo of him to some friends and asked if [they thought] I could voice him and they all said, "Oh, yes!"

It’s the most interesting playtime I’ve ever had as an actor. It’s about this feeling of going down a mysterious but joyful black hole, almost, where there’s nobody else there and there are directions being thrown at you by Tim, and once you relax after 15 or 20 minutes and say, ‘"OK, I don’t care if I look like an ass," it’s really fun to see what happens. You know that nothing is being visually judged in that way, and thank God, because I never left without being a sweaty mess, ever.”

Steve Martin: When I heard that Tim Johnson was directing I thought "Is he a foreigner? Because he has such an exotic name!" And I knew it would be interesting on that level. No, actually, I love the animated process because it’s kind of like writing a play in that you can try it out, you can change it, you can go back and experiment in 70 different ways.

When I saw the first animated sequences I was really astounded. I thought it was beautiful. So much emotion can be brought in an animated film that’s very hard to get in a live-action film — it might be because the characters can make facial expressions that if you made in a movie they would call them corny. But I find animated movies very touching. They reach an audience that is hard to get in live-action films. So I was thrilled to be in a movie that is so affecting, and with a fabulous leader and these two fantastic talents.”

Tim Johnson: I discovered the story through the book. Adam Rex wrote a book called “The True Meaning of Smek Day,” and it was something that I bought to read aloud to my boys, who were 5 and 7 at the time, after I had read great reviews. I read two chapters, tucked the boys into bed and then did something terrible: I cheated on my kids and stayed up the rest of the night and finished the book. And by the end of it I sent out an email, which I still have saved, with the 2 a.m. time stamp and the subject line saying “Dear Jeffrey [Katzenberg] — we’ve got to make this movie.” And it was the power of the characters — the comedy and beauty of the journey that they took.

Parsons: The little guy I play, the alien, he really comes in with a set of ideas about how the world is supposed to be, and he thinks that’s all good and right. He meets the character Rihanna plays, Tip, and learns what it is to accept other people who have different ways of doing things and whose beliefs may be different than yours. You can still be very, very close. That really resonates with me.

I thought a lot about being a gay person while making this movie, even though it has nothing to do specifically with that, at all. But being judged by something that people may not identify with or understand or have certain beliefs about, and then they get to know who you are — that’s just the one that I most personally identify with in that regard, obviously. It could be a million things. It’s important to take people at a different level than that, and let them be who they are, in their own hearts.

Rihanna: The microphone became the camera, in a way. I was definitely blessed to work with the opportunity to work with Tim Johnson. I know a great director only because I have no experience in this world. It’s nothing that I can really… I can think of a line one way, and he can put one word in my head, like "OK, so what if you’re eating pizza?" Like, something that silly, but right then and there he knows exactly how to get whatever emotion he needs in that moment. He’s going to be able to get it out of you.

And we had a lot of emotional moments in this film that I didn’t really expect. Because it’s an animated film you think it’s going to be all fun, but it’s so real that you really connect to the characters. There’s one specific moment in the movie that really wrecks me, and I feel like it’s going to [impact] everyone in the same way. When I was watching it for the first time it was just stick figures, it wasn’t even at the point where the animation was all finished, so I was bawling my eyes out and I was so embarrassed.

Johnson: It was really like having three partners – and I say that having made several other animated films and had a fantastic experiences, but the level at which each of these actors has had insight into their characters and taught me things about their characters [has been impressive]. There were early sessions with them where maybe I was doing a lot of the describing, but in the later sessions they know the characters better than I do, and it’s my job to basically just get out of the way. For me, it was a lesson in comedy and soulfulness, watching them each work.

Rihanna: I think that’s really what got me to even agree to do this: I felt like I identified with her. A lot of the way she thought, a lot of her flaws, her ambitions, her sass, her attitude — you can see them take my facial expressions and put them on her and it’s like, oh, God! But it’s really cool to see that happen.

Martin: I love these characters of dumb villains. I played one before in “Little Shop of Horrors,” and they always kind of resonate for me, and the audience somehow. So as we searched and found this character and kind of roamed around all over with him, the thing that kept coming up was dumb villain. I really enjoyed playing that, and it’s actually quite suited to me. I don’t know what that says.

Rihanna: The music is such an important and crucial part to the animated film. You don’t think about it, but you can watch “Tom & Jerry” for hours, and there’s no words. The music dictates the emotion, it dictates where the story is going or how you’re supposed to feel the suspense. Everything is in the music, so I worked very closely with Tim and Jeffrey Katzenberg, because I could bring them songs but if it didn’t move them or make sense in a certain part of the movie then it wouldn’t work.

Martin: Basically, I think films are about having a good time. There’s a message in the film about friendship and how valuable it is, but I wouldn’t want a kid to walk out and say, “Wow, friendship is valuable!” I just would really him rather say, “Gee, wasn’t it funny when this happened,” or “I cried when that happened.” And then they can connect with the message on an almost subliminal level, a week or even a year later. The message of a film is always what a critic writes about, and the fun or emotion of a film is what an audience feels.

Parsons: He’s right: the movie is about friendship, and you never know who it’s really going to be with. If you’re open to it, some real magic can come into your life that way. But I spent a brief period of time very early on working in day care, and we would play the same animated movies again and again, and kids always enjoyed them. I think with something like this movie the first hope would always be that it’s simply entertaining to them, and that any message of goodwill toward men or whatever it is embedded in the general tone. It’s fun enough to watch that you can absorb that message.

I’ve been so excited, too, about working on something so original. It is from source material, but not from [anything] that many people know of. There’s nothing wrong with recreating things, or with part twos and threes of things — God willing maybe we could on this movie — but for now, one of the things that’s so exciting to me is that it’s completely new characters and a really fresh story. And the animation looks brand new, too. It looks like they invented stuff for this.

Rihanna: Personally, for me, I felt like the message of the movie became clearer and clearer as it went on. You see these two individuals from completely different worlds and they have completely different ideas about who each other are, based on the worlds they come from and the different environments where they grew up, and by the end of the movie you start to see all these similarities being revealed and acknowledged between the two of them. That’s the basis of their friendship.

There’s this thing we have as humans where we judge each other, without even knowing or even having a conversation, really. By the end of the movie, they’re so similar that when you think back to the beginning of the movie when they first met, it really is like 180 degrees.

Johnson: If I had any message, it would be that a family with all ages can all see the same movie and all enjoy it together. As the father of a couple kids I find it increasingly hard to do that — to have an experience where we can sit down and laugh at different things, laugh at some of the same things, but have the experience that I feel I had frequently growing up, which is sharing something with my sister or my mom and dad. More than any of the messages in the film, I’m so proud to be a filmmaker at DreamWorks Animation, where we strive so hard to make sure we leave nobody behind — that an entire group of people can all have the shared experience of a powerful story.

”Home” opens today nationwide.