This is the first image of an aurora taken from the surface of Mars, or indeed the surface of any world other than our own. "But wait!" I hear you say. "I thought Mars didn't have a magnetosphere. How can it have an aurora?" A short 🔭🧵. physicsworld.com/a/this-is-wh...

It's true that Mars's magnetic field isn't as strong as Earth's. Earth has an internal magnetic dynamo. Mars doesn't, which is why it can't have nice things like liquid oceans and an atmosphere that protects its surface from intense radiation. But that doesn't make Mars a magnetism-free zone! (2/n)

Mars *had* a magnetic dynamo some 4 billion years ago. We're still not sure why it lost it. But that's not surprising, as we're also not entirely sure what causes Earth's dynamo, though the consensus is that a liquid core of magnetic metal probably has something to do with it. (3/n)

How does Earth's magnetic field give it oceans? Struggling to think of the causal links!