Alpha Geminorum

Alpha Geminorum was a star. To fool Luke Rattigan into having himself and the teenagers at the Rattigan Academy into helping the Sontarans (and later, being used as target practice), General Staal told Rattigan that he would take the group to "Castor 36", an Earth-like planet in the system, after "Planetfall". Only Rattigan fell for the trick, though. (DW: The Poison Sky)