Assume a newly discovered planetary system orbits a star exactly like the sun and that the system is the same age as our solar system. of the four planets described below, which one would you expect to have the coolest interior?
a. size: twice as big as earth. distance from sun: same as mercury. rotation rate: once every 6 months.
b. size: same as mars. distance from sun: same as earth. rotation rate: once every 18 hours.
c. size: same as the moon. distance from sun: same as mars. rotation rate: once every 10 days.
d. size: same as venus. distance from sun: same as mars. rotation rate: once every 25 hours.