Tarquin's planet was an unidentified class M planet once located in the Delphic Expanse. Cold and icy, its sole inhabitant was Tarquin, an exile condemned to live a life of isolation. Enterprise NX-01 visited Tarquin's planet in October of 2153 while searching for the Xindi weapon.
The planet was about thirty light years away from Tarquin's homeworld. It was located near Sphere 2 and a Xindi-Arboreal colony. (ENT: "Exile")
In the final draft script of "Exile", this planet was described thus; "It's covered with oceans, except for one mountainous continent."