The Sol system, otherwise referred to by UNSC personnel and Humans alike as the Solar System, is the home star system for Humans. The system's G-class star is named Sol, hence the system's name.
Mercury - Mercury is home to Antimatter production as well as solar research.
Earth - The Human/UNSC Headquarters (HQ)/Homeworld.
Mars - A major site of the Interplanetary War and later during the Human-Covenant war it was the site of the Battle of Mare Erythraeum. Has been terraformed to have an Earth-like climate.
Jupiter - A gas giant, Jupiter is the largest planet in the Sol System.
Saturn - A gas giant known for its clearly visible surrounding rings, unlike the other gas giants whose rings are rather dim. Saturn is the second largest planet in the Sol System. Its practical uses to the UNSC are limited, and therefore it is mostly just a tourist destination. It is alsothe site of Helium-3 mining and research habitats. 
 Uranus - An icy gas giant about twice as far away as Saturn from Sol. Its distance from Sol makes it of little use to the UNSC. However, the 2011 QF99 exclusion zone is around the planet.
 Neptune - Furthest away from Sol, it is another icy gas giant similar to Uranus.
Pluto - The Pluto Slipstream Monitoring Station is stationed in orbit around it. On November 3, Democritus 2552, the Monitoring Station detected Cortana's signal in Slipspace with Dr. Halsey's message to Lord Hood.
Shaw Institute Facility - Deep space observatory.
Sol is the original Latin and the actual scientific name for Earth's Sun. This designation and name has actually been used instead of "Solar System" in many Sci-fi novels.
The Covenant around Jupiter.