15. Will the asteroid belt be able to coalesce into a 9th planet with the current configuration of the solar system?

I

No.

Explanation:

No, the asteroid belt is not able to unite into a 9th planet because there is not enough total mass in the belt to form a planet. the other reason is that the belt is too close to Jupiter which make impossible to make the asteroid belt a planet. When this formation of new planet happens between the asteroid and Jupiter, Jupiter's gravitational forces act on the asteroid add up and strengthen each other, and they can easily kick the asteroid out of the solar system.

because the light is a great source of energy for the plants to survive. (i hope this )

layer 3 is younger than layer 6.