Why does Venus have an atmosphere?
It has not been explained to me why Venus has still got an atmosphere. Mars has lost its, no magnetosphere, but Venus is the same, so therefore it must be restored each time it is lost! Thank you for your interesting programme.
We put this to astronomer Matt Middleton, from the University of Cambridge...
Matt - So, a magnetosphere is incredibly important - the Earth has one. The Earth has one because we have a molten core that rotates, generates a magnetic field, a dynamo, and this magnetic field deflects particles that are coming to us from the Sun's highly charged magnetic particles. Now, if we didn't have a magnetosphere, the interaction would start to remove ions from the ionosphere, so our atmosphere would get leaky.
Now Mars doesn't have a magnetosphere; it used to probably around 4 billion years ago and we're not entirely clear why it went away. Now it's not just because it lost it's magnetosphere and everything just 'woo' off it went into space - that's the noise it makes actually. But, actually Mars is much smaller than the Earth and it has a gravitational field of roughly around 36% of Earth's, so holding onto stuff is actually very, very difficult.
Now if you go to Venus I would have to correct one of the things that was said. You're right, it doesn't have a magnetosphere but it has got something. It has an induced magnetosphere because the magnetic field from the Sun wraps around it, so it has some protection from the.
Kat - Is that because it's so close to the Sun?
Matt - Yes.
Kat - OK. So it's sort of hogging a bit of magnetic field from the Sun?
Matt - Yeah, yeah. Because magnetic fields are slamming into Venus and wrapping around so you end up with a sort of quasi magnetosphere.
Kat - Like a magnetic cuddle?
Matt - A big magnetic cuddle. That is the cutest thing I've ever heard in terms of planetary astrophysics.
Kat - And its holding some gas onto it like an atmosphere.
Matt - That's cute! Ah, I see a brand of toys emerging here. And Venus is very similar to Earth - it's essentially our twin planet. So it's heavy and that means it holds onto its gas so that is why it has more of an atmosphere.
Kat - Because of the magnetic cuddle.
Matt - Because of the magnetic cuddle.