Red giant will begin to expand into a subgiant. Eventually, the pressure builds up so much that the core will begin to fuse helium, and will expand even more into a red giant. At its largest, its surface (photosphere) will approximately reach the current orbit of Earth. It will then lose its atmosphere completely; its outer layers forming a planetary nebula and the core a white dwarf. The evolution of the Sun into and through the red-giant phase has been extensively modelled, but it remains unclear whether Earth will be engulfed by the Sun or will continue in orbit. The uncertainty arises
Gas giant electrical conductor. The gas giants' cores are thought to consist of heavier elements at such high temperatures (20,000 K) and pressures that their properties are poorly understood. The defining differences between a very low-mass brown dwarf and a gas giant (estimated at about 13 Jupiter masses) are debated. One school of thought is based on formation; the other, on the physics of the interior. Part of the debate concerns whether "brown dwarfs" must, by definition, have experienced nuclear fusion at some point in their history. The term "gas giant" was coined in 1952 by the science fiction writer James Blish