Essenus is a hydrogen-helium gas giant that was home to a substantial turian garrison defending the planet's fuel infrastructure. It once held a distribution center for antiproton-based fuel as well as the more common helium-3 collectors. The garrison is now gone. The Reapers drove the turians off and destroyed all available machinery.
The Reapers appear to have moved on. A few volus ships are now visible, likely present to scavenge the wreckage.