Saturn is the son of the shadow. Shadow is nothing but
a dark spot or spot without light. Such places can aptly be
described as ‘Sunless or Asurya (~ According to Isha
upanishada.

(Sunless are those worlds enveloped in blind gloom
whereto all they in their passing hence resort who are slayers
of the souls). It is on this account that Saturn is called Tamas.
Due to ignorance the soul becomes limited. It
differentiates itself from the soul absolute. The Taittiriya
Upanishad in chapter 7 says as per the translation of Sri
Aurobindo.
“But when the spirit that is within us makes for
himself even a little difference in the Eternal, then he
has fear, yea, the Eternal himself becomes a terror to
such a knower who thinks not.”
This explains why Saturn is called the ‘planet of fear
and worries etc.
Saturn is also called the lord Yama or the Lord of Death.
The literal meaning of the word death is death or the opposite
of life. It was not in this literal sense that the word was used
by our sages. Transformation from one life to another is one
of the important connotations of the word