Just found this out and wanted to share.
Loaded up a random Bugs of the System normal. Sent me to the future one. Cleared it easy enough, but then I saw the door wasn't completely barred shut like I thought it was. Sure enough, if you jump up to the hole? You can see inside the tomb.
Good show Bungie.
Now let us enjoy our missions whenever we want so more titans can kneel at the original badass who punched things.
-
You’ve probably seen this below, but keep chipping away at the prophecy weapons on Mercury, and it will open up a series or missions that will eventually lead you inside there. It’s actually pretty sweet. I won’t spoil what he’s surrounded by in there, but it’s pretty awesome.