Asteroid Magnetic Fields Lived To A Ripe Old Age
Scientists have determined that not only do asteroids retain a memory of their former magnetic fields, but that they lasted far longer than previously thought which could have implications for life in the universe.
Were you surprised just now that asteroids once had magnetic fields like the earth does? I had never really thought about that before but it does make sense now that I think about it. It’s just that they seem like such utterly dead pieces of rock and metal, that any activity, even magnetic, seems slightly odd to me. Of course they were not always so inert.
The prevailing thoughts on this, until now, was that molten metal in asteroid’s cores moved around after their initial formation. Just as in the earth, this flow of iron creates electric currents, generating, in turn, a magnetic field. Due to their size and relatively rapid cooling, it seemed reasonable to assume that this field would only last for a few thousand years before the core froze solid collapsing any field it had been faithfully generating for centuries.
Testing this assumption however has always been thought to be futile because iron (common in metal-rich asteroids) is terrible at remembering the long lost magnetic fields it had once been exposed to. Ever see a hard-drive based on iron? Well, that’s why.
A way around this was found recently by a team at Cambridge’s Department of Earth Sciences in the UK. They studied meteorites containing nanoscale grains of an unusual magnetic material called tetrataenite. This material is so stable that it contains a history of its parent body’s magnetic field going back billions of years (I’d love to have a hard drive made of that stuff).
Using magnetic microscopy followed by computer simulations, the scientists and engineers were able to determine that the magnetic field of the meteorite was created based on its composition and not just because of thermal convection as earth’s is. This means that the field was not only powerful and widespread but it could have lasted not thousands of years but millions to tens of millions of years.
One ramification of this discovery applies to the idea of panspermia. This describes the theory that complex organic material from one planet can travel through space, eventually seeding another planet with life. If asteroids and meteoroids can maintain magnetic fields for extended periods of time, that means that panspermic material could conceivably have a nice place to hang out for a long time, safe from cosmic radiation, before it finds itself on another planet where it can germinate.
Another benefit of this news relates to this quote by planetary scientists James Bryson of the University of Cambridge:
“The fact that you can get this very efficient, very long-lived magnetic activity on asteroids is really going to change the perspective on how we think these things evolved…And from an even wider perspective, I think it’s also becoming incredibly apparent that asteroids in many ways are just small, sped-up versions of our own planet.”
This parallel between asteroids and planets is an intriguing observation. This means that by studying the evolution of asteroid’s magnetic fields, we could potentially elucidate the history and future of our own magnetic field. No need to worry though about our own protective shield imminently collapsing like that of an asteroid’s. Our magnetic field will likely last for longer than it takes the sun to fry our planet into a desiccated husk removing all evidence that any life ever existed on it.
Image Credit: Space.com