Tom Van Flandern is an astronomer
who has purposed theories and
searched for Planet X. He is mentioned by the Planet X crowd frequently.
I found this interview of Van
Flandern on the Laura Lee show. He discusses
the foundation of Sithcin's theories of the 12th planet, the Akkadian Seal
from the ancient Sumerians. The seal is the key that Sitchin uses to interpret
other translated Sumerian works to relate to ancient astronauts. From an
astronomers point of view, the seal does not depict our solar system and
there are several inconsistencies.
Laura Lee Interview
Below are a picture of the Akkadian
Seal and a drawing of the section that
Sitchin interpreted to be our solar system.