Need help to ID a book
 

I do not know the author or the title though I think it was something like "inner heat" or "earth heat"
It was a sci fi book that came out in the mid to late 80s or early 90s. It takes place initially in a subteranean city where the magma used to heat and power the city is slowly receding. The reason humans retreated underground is that aliens stole the sun. The hero has to escape to the surface of the earth , which the gov of the city claim is frozen and uninhabitable. turns out that it is inhabitable because the aliens set up the theft of the sun to cause Jupiter and Saturn to collide and become a new sun.

Any help is apreciated.

Possibly this?