The article states:
"He claims Lewis' knowledge of medieval history, of which he was one of the leading scholars, made him familiar with the characteristics attributed to the seven planets during the period. Each of these planets gives one of the books its theme. Prince Caspian, for example, is a story ruled by Mars, who is manifested by soldiery and battle, while The Voyage of the Dawn Treader focuses on the Sun, with its light and gold themes. In The Horse and His Boy, based on Mercury, the planet that rules the star sign Gemini and is associated with the power of communication, the characters include twins and a talking horse."
While I do believe it is likely that there could be a secret theme behind the stories, I am a bit hesitant to take this theory to heart.
Lewis's Christian allegory runs thick throughout the Narnia stories and it is not hard to pick out these references, such as Aslan's depiction to Christ. But a secret theme aligning with the planets seems a bit...well...out there.
Dr. Ward's book, Planet Narnia, and his official website can be found here: Planet Narnia
What are your thoughts? Could Lewis have been weaving in a secret theme throughout the Chronicles of Narnia without disclosing such information? If so, why do you think he would he have done such a thing?