I'm not a pkg expert but it looks like the explorer pkg that you want to install is a later version (...220.127.116.11.24.0) then the required pkg dependency, which is is at ...127.0.0.0.2.1.
I would guess that the solution is to create a new BE (for safety) and pkg update the existing BE. Then, try installing the explorer pkg again.
I think there is a pkg update mode that will show the changes that will be made without actually applying the changes. That's another option.
Check if you are really Solaris 11 installed and not an older version.
In the case that you have an older version, please update your system if you can and try again to install Explorer.