In a few billion years when the sun expands and grows into a red giant, how fast will it expand and “swallow” the inner planets?

Question

In a few billion years when the sun expands and grows into a red giant, how fast will it expand and “swallow” the inner planets?

In: Physics

Answer 1

I read that when the Sun puffs up into a red giant and ‘swallows’ some inner planets .. they will actually continue along their normal orbits INSIDE THE SUN!

Is this true?
If so, how long will they last before getting ‘absorbed’ ?