Legal Aware via Twitter asked:
What is the oldest known planet in our universe and how would we know that?
Dominic - That is a very tough one. Itís very difficult to age planets outside our own solar system because we don't know what they are made of. We can only see their gravitational influence on other bodies.
So, it would have to be a planet in our solar system which is about 4.5 to 5 billion years old. So, it would really be all of the planets in our solar system about the same age of about 5 billion years.
Chris - But there will inevitably be older ones out there that we can't see yet?
Dominic - Yes.