Gyre was colonized in the 22nd century by the newly established ISA, and was found to have a surprisingly oxygen rich, breathable atmosphere, eliminating most of the terraforming process. Gyre is smaller and colder than Vekta, largely ocean, and with millions of tiny islands dotting the surface. It is likely that it may be a holiday destination for the Earth's and Vekta's civilians. By the 2300s, Gyre's native population may be in either hundreds of millions or billions.
The colony could be under threat from the Helghast, and if it was invaded by them, it would take weeks for the ISA or UCN to assist and Gyre would fall to the Helghast in a matter of hours like Vekta did, likely having a weaker ISA presence than their neighbor. However, Scolar Visari is more interested in the planet Vekta as it was the home that the UCN and ISA forced the Helghast people from.
There is another planet that may be even further away from Earth than Gyre is all together called Zeronus, but its location is unknown.
As of the end of Killzone: Shadow Fall, Gyre is engaged in negotiations with Helghast Labor Unions, and has a majority of Helghast in its Senate.