That sounds like the title of a really bad B movie from the 1950s but these two are not fictional and really do move in strange ways.
I’ve written many times about how the solar system we see is the result of order coming from chaos, and the fundamental force (that gave us not only our Sun, planets, and the whole universe) is gravity. Last month I explained why everything in the universe spins and that in our solar system every planet and moon spins the same way. I lied, quite deliberately to keep things simple, so now I’ll try and sort that out. There are lots of little rocks etc floating around in space that spin wherever chance takes them after hitting each other, but there are two big things that are really odd and seem to break the rules, the planet Venus and Neptune’s biggest moon, Triton.
Every moon that orbits a planet goes around in the same direction that the planet spins, that’s the way planetary physics works, except that Triton doesn’t, it orbits in the opposite direction, the only moon to do so. So why does it do that, is Physics wrong? Neptune is the furthest planet from the Sun, it’s also the nearest planet to a vast area called the Kuiper belt, a place in space where lots of minor planets like Pluto, Makemake and many others orbit. We think that aeons ago there was a collision that sent a minor planet inwards and it got caught by Neptune’s gravity but at an angle that made it circle in the wrong direction. As you would expect, this isn’t a stable situation and in millions of years gravity will probably break Triton up and there might be a new ringed planet in the solar system, you can’t beat physics!
Now for Venus, the nearest planet to Earth (sort of), this is a very strange place. Firstly all the other planets spin in a clockwise direction, Venus in an anticlockwise direction. Next, it does this very slowly, Earth takes 24 hours to spin once, that’s our day. Venus takes 243 Earth days to spin once, that’s a very long day. Couple with this that it takes 225 Earth days to circle the Sun, one Venusian year.
The strange result of this is that a Venusian day lasts longer than a Venusian year, and the Sun will rise in the west and set in the east, an odd place isn’t it?
Why is Venus like this? The truth is that we aren’t sure, but like so many other planets and moons, it was probably hit by something else in the very early history of the solar system, and this collision actually turned the planet upside down. If this is correct Venus used to spin the same way as the other planets but as one professor put it, ‘Venus is arse upwards!’
That’s all for now, next month I’ll tell you how you should be pronouncing Uranus, and why that’s another strange place.