In relation to all of the above, I would like to outline an alternate solar-system and planet formation concept involving the outward trajectory of planets, and the transformation from rock planet to gas giant, which negates Accretion as the main planetary formation process, but which gives it a significant role at the later stage of transformation and in the early period of creating the 'ecosphere' in the first place. It is this outward trajectory of early gas planets that is the key to the creation of this area within which life is possible, known as the 'protected zone', 'Goldilocks Zone', or ecosphere.

To refer back to the ‘Transitters’ section; HD 209458, although lighter than Jupiter, is bloated to a diameter 35 percent greater. This planet, and others like it, suggests that Roasters and Eccentric Giants are less dense than the gas planets of this solar system.

To refer back to the ‘Intermediate World’ section, the planet orbiting Gliese 876, which is intermediate between a true terrestrial planet like the Earth and a hot version of the ice giants Uranus and Neptune, also fits into the sequence of this alternate formation concept.

To begin to build a timeline from the first gas planets to emerge from the disk, it would begin with something like HD 209458, and at a later stage it would be followed by something like the planet orbiting Gliese 876.

Here are their technical details again;

HD 209458, is far less dense than our gas planets. Although lighter than Jupiter, this is bloated to a diameter 35 percent greater. It consists of hydrogen, helium, and sodium, and is slowly evaporating in the heat.

The planet orbiting Gliese 876 is over 7 times Earth’s size with 6 times its mass. It is intermediate between HD 209458 and a rock planet like Earth.