"Battle of the Worlds"(1961)?

Here is the entire movie from YouTube. If you go to 1:22:00, you will see an astronaut saying goodbye to the old scientist (played by Claude Raines) as they head back to earth.

https://www.youtube.com/watch?v=mQXrTt7mJ-I

And at 1:22:42 you can see the scientist's dog eagerly awaiting his return. I can see why it would make someone sad! Also the interior of the planet has reddish tubes hanging down everywhere and the runaway planet is controlled by an artificial alien brain? Oh well, it seems to match the story points you listed.