The Planet Venus
But it seems these identical twins developed in very different ways...OK, that's after a cursory read by a lay-person of this very interesting piece:
"One day on Venus, which alone of all the planets rotates backwards, lasts 243 Earth days. The planet's air is thick, at 90 times the pressure at sea level on Earth, and there are dense clouds of sulphuric acid. Violent winds race around 50 times faster than the planet spins, and vast hurricanes hang over each pole. The surface is paved with basalt dating from planet-wide eruptions no more than 500m years ago."
I have loved planets ever since the terrific BBC series The Planets in 1999. It may be a little dated by now, but it inspired a few poems at the time.
The Venus Express will soon be on its way there, to be launched 26 October. Follow its progress from here.