Planets are a group of colonies, or players. Each planet needs a Planetary Commander (PC) and Minister of Development (MoD) to manage common affairs. A planetary commander may be elected from the affairs view who then appoints the MoD.
The Planetary Commander sets the planet name, appoints the MoD and can choose a picture for you planet. He may also initiate kick votes for players who are not wanted in the planet. The PC should strive to work for the planets best interest and acts as the voice for the planet in the galaxy.
Only the MoD can view donation and start projects. Planetary projects help everyone in the planet and aren't exactly cheap to complete. The benefits of a completed planetary project are immense and often require that each and every colony in the planet works together.