As noted by @schaiba and @Romeo Ninov, for the initial install for Solaris 11, root is created as a role. But the install process also asks you for an initial user which it will create with "admin" privs. Using this initial account you can use su or sudo to assume the root role.
Let's confirm the RBAC settings for root.
As you can see, the type is a role.
And it's set to use the users authentication (pw) to assume the role. Which allows us to not have to manage a root passwd.
getent user_attr root