Partholon

Mass Effect 2
A large planet composed of ice surrounding a rocky core, Partholon retains trace gases of nitrogen and carbon monoxide. Its crushing gravity makes for an inhospitable stay and makes most mining infeasible. However, its orbit's proximity to the mass relay in the system means space travelers will, for the next few years, use it for a gravitational slingshot to add speed on their way to and from Caleston.

Mass Effect 3
A large planet composed of ice surrounding a rocky core, Partholon retains trace gases of nitrogen and carbon monoxide. Its crushing gravity makes for an inhospitable stay and makes mining largely infeasible. However, its orbit's proximity to the mass relay in the system means space travelers will, for the next few years, use it for a gravitational slingshot to add speed on their way to and from Caleston.