system
Given the following post, respond as if you're commenting on Reddit:
human
How would our solar system change after the sun goes into its first red giant phase?

The Earth would be swallowed up most likely, and Mars would become insanely hot, but what about the gas giants?  They are adequately far away, yet they might be close enough for some or most of the gas layers to boil away.  Would the small rocky cores become new planets, rather large, and with very heavy gravity?  Would new ecosystems form over time?  I am very curious.

EDIT: Pretty much what I expected.  As in, who the hell knows LOL.  I absolutely love astronomy and long term thinking, you know big picture stuff, and I love to get people to start talking about these sort of topics.  Keep them coming.
gpt
Not exactly on topic but since you brought up atmosphere boiling away.  When humans consider our cosmological impermanence it is widely known in popular culture that our sun will one day become a red giant and either destroy or render our planet inhabitable wiping out everything we currently know.  Even though this is roughly 5 billion years in the future it is still irksome.  

What is not as well known is that our planet's biosphere will be destroyed by our sun much sooner than that.  The sun is constantly increasing in intensity as its hydrogen supply dwindles and in only 1 billion years it will be hot enough to cause Earth's oceans to evaporate and be lost to space.  A billion years after that the remaining atmosphere will be gone leaving Earth a desiccated, dead planet with a surface of molten rock.