When communications with the Venkatsen Research Group were lost, the U.S.S. Enterprise was sent to investigate. In a system with 47 planets, the transporter is not usable, so Kirk and crew take a shuttle to Hohweyn VII.
The situation where communication with the Venkatsen Research Group was lost led to the U.S.S. Enterprise being dispatched to investigate.  Because of the lack of transporter functionality in the system's 47 planets, Kirk and his crew traveled to Hohweyn VII using a shuttle.