Venus has been hard to ignore in the evening sky these last few months, and it’s helped rekindle my love of city astronomy. It’s not that I’d ever lost the habit of looking up as soon as I step outside, it’s just that I’d begun to long for trips outside of town to see a properly dark sky. The searchlight of Venus shining in the west has been a reminder that even from the most light polluted spot you can watch the slow dance of the sky as the months go by, and that’s partly why we chose it as the star of the show for the first Living Space podcast.

I’ve been keeping up with the latest results from Venus Express, and looking forward to whatever Messenger will have provided during it’s last swing past yesterday, but it’s been a long while since I did any background reading on the Earth’s evil twin. I was therefore surprised when interviewing Fred Taylor for the podcast when he said confidently that there must have been oceans on Venus. I knew it had long been suspected that there was water, carried to the young planet’s surface by comets or contained in the gas released from volcanoes (and Venus certainly was and maybe still is a volcanic planet). But whole oceans? Where did all that water go?

The usual reason given for studying Venus (and other small, rocky balls like Mars) is that we can test our models of how atmospheres work, and then apply the results to Earth. Rather wonderfully, while reading up on the background following Fred’s interview, I found a wonderful piece of work from five years ago which applies what we already know about Earth to Venus. Researchers from NASA studied the only place on Earth where a ‘runaway greenhouse’ effect applies – a place where more energy is being absorbed from the Sun by the Earth’s surface than can be emitted. This is a runaway effect because the hotter the surface gets, the more energy it can absorb.

On Earth, there’s (currently – see the comments on this post below for the latest discussion here of our attempts to warm the planet) only one place where this happens (in the Pacific, just NE of Australia) but this must be what happened across the whole of Venus billions of years ago.

The moral of the story? The more we study all of the planets, including Earth, the more we learn about all of them. And that you should go and listen to Fred’s interview over at Living Space. It’ll be joined by a new podcast coming on Friday.