There are 3 main levels of devatas (deities) for each planet.

1. Graha Devata
2. Adhi Devata
3. Pratyadi Devata

In the Navagraha Suktam there are verses for each of the 3 type of Devatas.
The Graha Devata relates to the physical, Adhi Devata to mental and Pratyadi Devata relates to the soul level.
The Graha Devata works on the material level to help you through the nature of the planet. The Adhi Devata helps you understand the nature of the planet. By understanding the Adhi Devata you can understand the basic instinct of the planet. The planet Sun’s Adhi Devata is Agni (Fire element) so you know that the nature of the sun is fire and light! It also represents our ego! Similary for moon it is Apas (water element) – water represents our mind and emotions!

The Pratyadi Devata helps you understand the way the planet will function.
Lord Shiva is the Pratyadi Devata of Sun. Shiva represents the unmanifested consciousness and his purpose is making us realize our own self! And thus the planet sun always represents our soul as well! The Pratyadi Devata of mercury is Lord Vishnu and this denotes the practical sustaining force of the universe.

One school of thought also mentions about the activation of planets through their Devatas. For Rashi chart it is the Graha Devata, D9 – Adhi Devata and D60 – Pratyadi Devata.

Below is the table showing the Graha Devata, Adhi Devata and Pratyadi Devata of all planets!