“ This implies an atmosphere in space, which is normally a vacuum..”
Not near a star it isn’t. Charged particles and solar mass ejections would provide drag.
L
I wont disagree in general to your statement, but its the amount of drag that needs to be explained. We send probes around the sun all the time now. Mercury is in the same orbits its been in for billions of years.
If this planet was so close to its sun that it spiraled in like described, then this star and its planets must have been in the formative stages and this was never really a stable planet.
The story leaves a lot to be explained.