Sorry for being a party pooper with the link, Jack. I think you have raised an interesting topic for discussion and I wanted to put here the link to the programme for anyone who is interested.
There are several issues here aren’t there – for example about how one interprets a loose statement like ‘Mars, our nearest neighbour’ that was used on the Sky at Night. Of course, as people have pointed out, ‘which planet can get closest to Earth?’ is a quite different question to ‘which planet is most often the closest to Earth?’, and indeed ‘which planet is closest to Earth now (or indeed any specified time)?’.
Revealingly, Chris Lintott, an accomplished astrophysicist, checked that Mars was closer than Venus at the time of broadcast, but didn’t even think to check the distance to Mercury at that time. I am not saying any of you are guilty of this, but I think we can probably say that many people will just think of the sequence of orbital ellipses around the sun and conclude ‘it must be either Venus or Mars, mustn’t it.’
Also interesting is that (I hope I recall this correctly) the programme researchers looked through articles around this topic and found that there wasn’t anything published on this question. On something so simple, this is very interesting.
P.S. I second Jeremy’s point about More or Less. I subscribe to the podcast. I was hooting with laughter as Tim Harford took a nutritionist to task about the difference between ‘facts’ and what might be ‘good policy’ – relating to data on sugar consumption over time.