What is the difference in the Halo 3 endings?

[Batista]

I have seen the legendary ending and went back and played the heroic ending and they look exactly the same.

 

[Nino]

Alright, you just have to wait until after the credits on the legendary ending to see the bonus ending. Thats all.

Also the planet thing is not Marathon, it doesnt have an official name yet. I know pretty much everything about halo, and my best quess would be (since the code name to the game in production now is "Forerunner) that the planets name is Onyx. Which was a planet created by the forerunners, to protect themselves against the explosion of the halo rings. To survive the blast.

 

[Honchy]

The part where they're in the ship and they pass the big, robotic planet (Marathon). It leaves it open for the game Marathon, the game the guy that answered after me mentioned.

 

[II_Epsilon001_II]

One you see the planet the other is you see Master Chief seal himself in a cryotube and the end music plays out

 

[Mike S]

You have to do EVERYTHING in the game to get the secret ending. Basically, it shows Chief still lived and leaves it open for another game, which I don't recall the name of, that Bungie made YEARS before Halo.