Water? The sun. I DUNNO I FEEL BAD :(
This means acceleration a is constant.
Let
a) vo be the initial speed, at t=0
b) v be the final speed after time t
c) d distance travelled in time t
Then we have:
a) v=vo+a×t
b) v²=vo²+2×a×d (Galilei's equation)
c) d=vo×t+a×t²/2
d) average speed vm=(vo+v)/2
I think the main idea is that the middle planets have a solid inner core and that they all could have life on them
