Not to add another layer to what is already a complex problem, but ...
One of the things that jumped out at me in the
Krypton Glossary is the fact that eighteen Kryptonian years is equal to 25 Earth years. Basically, this means that by the time Earth has complete 25 orbits of the sun, Krypton had completed 18 of its primary.
All well and good, but when one takes into account the massive nature of the planet as calculated, one discovers that Krypton is
screaming around its primary at a velocity unheard-of for a planet that massive. By way of comparison, the massive planets of our own solar system orbit their primaries in periods better-measured by Earth
decades.
This naturally brings to mind speculation about the distance between Krypton and its primary. Krypton's primary must have been a red giant, after all -- meaning the star was far more massive than our own G-type yellow sun. I don't know the math to check this, but I would have to assume that a planet that massive careening around its primary at that speed would have to be an inner planet, otherwise its velocity would overcome the gravitic pull of the primary and send it off into space.
Again, I don't know the math, but since you've calculated both the mass and size of Krypton, it might be interesting to know just how close it would have to be to the primary to keep from flying off into space.
The known factors in the equation are the mass of Krypton and its orbital period (one orbit of the primary every 1.3889 Earth years). The unknown factor is the mass of Krypton's primary. One could substitute the mass of a known red giant for Krypton's primary and see where the figures take you.
Dakota Smith