The Heart of Deimos is a quest added in the newest patch to Warframe. The new quest introduces a new open-world area on a completely new planet. Players journeying to the planet will uncover a wide array of new threats and a bunch of cool new toys. Chief among these is the new Nercemechs, giant robots with some very vicious combat abilities. Players can eventually claim one of these as their own, but first, you have to start the Heart of Deimos quest.
To start the start the Heart of Deimos quest is pretty simple. When you log in after patching the game, you should see a message in your in-game inbox. Read the message from Loid to get started.
To actually get into the quest itself, you just need to open up the Codex. The Codex is right at the front of the ship. Open it up and select the Heart of Deimos option to start the Heart of Deimos quest.
Open up the Star Chart and scroll over to the Deimos nodes on the map. Look directly beside Mars if you can’t find them. The first one that should be unlocked is called the Cambion Drift node. This is the new hub world for the planet, offering access to vendors, quest givers, and more for new players.
When you load into the mission you will be guided through a simple mission that has you destroying a Hive. The NPC will guide you through a few waypoints and eventually, you will be tasked with taking out a few more Hives. From there, you get access to the true social hub of the planet, the Necralisk. From there you can claim bounties and explore the area as you wish.