In our solar system most of the heat once stored inside the planets has leaked to their surfaces, and been radiated away. As a result, the heat of the Sun is the primary source of heat at their surfaces. read more
So yeah, those planets are cold (because the distances are so large), but it's nothing when you look at the universe as a whole. It's chilly (and dark, for the same reasons as why it's cold) out there. read more
As the eight planet from our Sun, it is now the outermost planet in the Solar System, and hence the coldest. Orbit and Distance: With an average distance (semi-major axis) of 4,504,450,000 km (2,798,935,466.87 mi or 30.11 AU), Neptune is the farthest planet from the Sun. read more
With a mean density of 0.687 g/cm 3, Saturn is the only planet in the Solar System that is less dense than water; which means that it lacks a definite surface, but is believed to have a solid core. This is due to the fact that Saturn’s temperature, pressure, and density all rise steadily toward the core. read more