Here's a more accurate map, I recommend this.
http://www.reddit.com/r/DestinyTheGame/comments/36349w/guide_ether_chests_locations_found/
After killing the target you only have 1 a minute and a half to find the chest.
If you find a chest try to tell other guardians
It's possible the locations randomize
Where I've found the chests after defeating the target
Forgetten Shore : Near the ship the Fallen occupy, middle ship, small ship near the Warmind building
Skywatch: (Building not the hive crash sight)
Near the downed helicopter next to the shack
On top of the building
Inside the building
Near the entrance to the Mothyards
Ember Caves : The cave leading to the Aksor strike, near the yellow captain
On top of one of the mountains
The Citadel : Near the exit to the endless steps right by to the side and by the entrance from Ember Caves
Tips: Use a sniper to look for green light pillars, they're narrow so look hard.
Use arc damage for shield takedowns
Super Important: Dieing before you get the key will result in you not receiving it, be cautious
Help me by posting where you've found chests and I'll help the community
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Just got a key :D