Time

Listening to an episode of Planetary Radio, the guest was asked where, if not Mars, in the solar system might life be found. I was surprised his answer was Europa - I've become accustomed to scientists saying Enceladus.

Then I realised that of course, this episode was recorded early 2003. The geysers of Enceladus had not yet been discovered. In fact, Cassini had not yet reached Saturn and Galileo still orbited Jupiter.

This also reminded me that Mike Brown had not yet discovered Eris, nor most of the other dwarf planets he is famous for, the Kuiper Belt is far less populated in our knowledge and Pluto as yet relatively firmly regarded as a planet is.

So much has changed in our understanding of the solar system over the past decade.