SPARTAN-IIIs Kat-B320 and Jun-A266 were from New Harmony. Sometime prior to 2537, a battle took place on this planet between Covenant and UNSC forces. The UNSC successfully defended the planet and won a rare naval victory. During the battle, a prowler, the UNSC Razor's Edge, managed to attach a telemetry probe to a retreating Covenant frigate, allowing it to track the ship and locate K7-49.
In the Epilogue of Halo 4, Thomas Lasky mentions that he grew up "on" New Harmony. While the preposition suggests he is referring to the colony world, it is more likely that he is meant to be referencing the city of the same name on Mars, which is established to be his homeworld in Halo 4: Forward Unto Dawn; furthermore, it is mentioned in the fourth issue of Halo: Escalation that Lasky grew up with Petra Janecek on Mars, suggesting the use of the preposition "on" was a mistake or that the details of Lasky's background were changed later on in production.