I was having a hard time getting this to unlock because I know I had been to all Lantern Planets (I had completed most tasks) but yet this achievement had not unlocked. Then I decided to do all planets back to back in one go. I went to the moon hub and traveled to each planet, once I traveled to the planet, I traveled back to the moon and then went straight to the next planet. Once I reached the seventh planet the achievement unlocked. It seems you might have to visit each planet in succession or all in one go.
I have also heard rumors that you might have had to unlock the Green Loontern, but I can neither confirm or deny this. Six planet hubs are located in the Moon Base building (Nok, Zamaron, Odym, Okaara, Qward, and Ysmault) the seventh hub (Oa) is located on the moon on the opposite side of the planet as the Moon Base building.
Apostle92627 confirms that you do not need Green Loontern to get this.