Why does Venus spin in a different direction?

05 December 2017




Why is Venus the only planet in our solar system that rotates clockwise while the others rotate counter-clockwise?


Astrophysicist, Matt Middleton, had Chris Smith and everyone in the studio spinning with his answer to Connie's question, does Venus rotate the "wrong way"?

Matt - I try not to judge but you're absolutely right. Basically all the planets, the way that we view it, they all rotate counter-clockwise. If we were to stand above the solar system the Sun is spinning counter-clockwise, the planets are orbiting counter-clockwise and they're spinning counter-clockwise with two notable exceptions.

It’s not just Venus actually, Uranus is also tilted so it’s actually got its poles aligned with what we call the ecliptic, so it’s been knocked over 90 degrees roughly. Venus, on the other hand is completely upside down, the way that we see it, so it’s been flipped. There’s a few ideas, unfortunately, it’s quite unsatisfactory, there isn’t a solid answer yet, but the idea is that maybe there was some sort of interaction in the early solar system. There’s this thing called planetesimals which were flying around doing all sorts of things, interacting, bumping into stuff. It’s possible that there was some sort of collision in its lifetime that flipped it. So from Venus’s perspective everything’s normal. It’s not done anything; it’s still spinning the right way; it’s just had a bad experience; it has just had a bad day.

The other possibility, which people are investigating, is that could it have actually slowed and then started spinning in the other direction? These are still unanswered questions.

Chris - Would that be a bit like you can do the experiment with an egg. If you spin an egg, put your finger on and stop it, take your finger off, and because the innards of the egg have momentum they can make the egg spin? Is someone saying Venus could have something similar to that going on?

Matt - It’s possible. I think they’re mostly investigating the tidal interactions between the Sun and Venus because Venus has got an incredibly dense atmosphere. You're probably talking about an incredible amount of time. But interesting egg analogy, I’m sure they’ll be people listening and thinking oh, that’s my next research paper.

Chris - Kate?

Kate - What kind of experiments do you do to test these sorts of things?

Matt - Expensive ones.

Kate - Are they expensive computationally? Coming from biology I’ve no idea what I would do.

Matt - In order to get to the answer we have to understand the early time during the solar system, and that’s not an easy thing to do. There are still some rocks flying around that we can look at. There’s all these carbonaceous meteorites, all these things from very early on in the solar system, but really we need to study things like Jupiter, believe it or not, because we need to understand what it’s made of because that tells us about how the early solar system evolved. There’s some evidence to imply that Jupiter migrated from the outer solar system inwards and which would mean it has a different chemical composition to what it would have if it was born in situ. So we have to explore these things to understand how did the solar system develop. Maybe that will give us some answers, maybe it won’t. What I know is it’s not going to change the way Venus is spinning.


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