E de Dave Kornreich em contradição com outras resposta já aqui expostas:

"It sounds like you're mixing up the concepts of a protoplanetary core in
Jupiter and Jupiter's density distribution. The article you reference is
referring to new data that might indicate that Jupiter did not form by first
forming as a rocky planet, then attracting gas from the nebula via gravity.
This would be the "rocky core" concept on Jupiter. But if such a core did
once exist, it would have long since been smashed into degenerate material,
like the rest of the interior of Jupiter.

That Jupiter has a small moment of inertia simply means that its density
increases with depth. That's a different statement than the use of the word
"core" in the article."