Some planets have no docking ring. These are unexplored planets just waiting for YOU to explore them. To do this, you will need to acquire a Planetary Landing Module and some Exploration Deploy Kits. The PLM can only be gotten from as the final reward from an NPC in the Palolon System.
The EDKs come in three forms, Basic, Generic, and Advanced. They can be made by Players, or can be found inside certain locked cases. Each EDK is rated for a certain level of danger. On some planets you will only need the Basic EDKs, while others will require Advanced EDKs.
Jian and Cradle, in the Kelsey system, are not explorable. At the time of this writing, these planets are not approachable.