Gharusa Prime was a planet.
Once, Addison Delamar send a transmission from there, disguised as Jack Harkness to lure the Doctor to Gharusa Prime, so she could buy Jack's body scan info from the Slitheen foundry on Gharusa Prime in the first place. (COMIC: The Bidding War) This was part of her plan to capture the Doctor to sell his memories to the highest bidder after he put his brain up for auction. (COMIC: Weapons of Past Destruction)
The Doctor recognised Gharusa Prime because of a skyscraper in the background of the video, the Delamar Solar-Needle. Therefore, they went to Gharusa Prime to investigate the origins of the message and discover why Jack couldn't remember sending it. (COMIC: Doctormania)