what is the oldest planet?

Question: what is the oldest planet?
- Keywords:
  planet,
  space,
  time
Asked by travisblundell to Cathal, Daphne, Darren, Jon, Katherine on 14 Mar 2012.
- Katherine Haxton answered on 14 Mar 2012:
  
  I googled ‘oldest planet’ and the Hubble space telescope discovered the oldest known planet back in 2003. They thought it was 13 billion years old! Planet Earth is only 4.6 billion years old.

Question: what is the oldest planet?