The hydrogen and helium gases are too light to be held by these small planet's gravity. The outer planets formed in a cooler part of the nebula and were able to retain the ices. The largest four were able to hang on to the hydrogen and helium as well, and resemble the sun very closely in overall composition. Page 39, Figure 2.16. The halo is too faint to appear on this photograph.
Nobody has any idea about the temperature or nature of the missing mass.
After this, the sun will remain a somewhat dimmer red giant for a few more 100 million years before brightening and undergoing a final phase of mass loss ending in a planetary nebula. The description of a degenerate gas is wrong. The electrons are always separate from the nucleus. The temperature has very little to do with a degenerate gas. Electron degeneracy occurs when electrons are crammed so close to each other that they fill all available quantum states.