Question: what is the coldest planet in galaxy

Niamh Shaw answered on 8 Mar 2016:

Well we haven’t explored all the planets in our galaxy, at the moment, theres an estimate that there could be 40billion planetary systems (like our solar system) and we have only just begun exploring all the different planets in just some small isolated parts of our galaxy. We still have lots of research to do. But within our own solar system, the coldest planet would be Neptune. BUT recent evidence may indicate the existence of a ninth planet, Planet X within our solar system which is about 20 times father away from the sun than Neptune and if this is the case, then this planet would most certainly be the coldest planet in our solar system. For now. The more we explore, the more we have to update what we know of course. That whats great about Space. The more we know, the more we know we don’t know.

As a rule of thumb, planets that are farthest from the star they are orbiting within a specific planetary system are usually the coldest, because they are too far away to benefit from the heat of the sun.