The only remaining Orokin Towers are hidden here. The Grineer patrol this area to prevent Tenno incursion.
Mercury is a planet where the Grineer are the controlling faction.
The vital target of the planet is Captain Vor, who is located in the mission Tolstoj and has a chance to drop blueprints for the Cronus longsword and his personal sidearm, the Seer. He also has a higher than average chance to drop Morphics.