As an adverb, so is associated with the conjunction that and means "enough." Very means "extremely."
The moon is so close to the earth
that its gravitational effects are readily
observable through the tides of the oceans.
Surface temperatures on Mercury are very
Do not use so to mean extremely. Use very.
Mercury is so close to the sun.
Mercury is very close to the
The word very can often be omitted, and when it can be it should be.
Mecury is close to the sun.