So I have stumbled upon a secret location on Mars when a Cabal Phlanax had smacked me into oblivion, but I did some searching around and I found this Gem check it out:
Edit: Apparently some one has already found this and I wasn't aware at the time of posting this.
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Don't worry man, this game is so huge, so many people have played it, so little information on all the secrets is known, and Luke Smith is very secretive of hidden content, he even said it himself, there are secrets in the game and we won't tell you where they are. I wouldn't be surprised if some of those exotics in the grimoire just haven't been found yet because they are secretly hidden in the game (personally if I found one, I wouldn't tell anyone, greedy or not, it'd be like The Fate of All Fools, why ruin a surprise?). Also... I think they've been dropping hints with Bones of Eao, that extra jump goes a long way and you could get to places no other guardian can reach.