Friday, April 17, 2015

Early Earth Ate a Mercury-Like Planet

A Mercury-like body smashed into a young Earth and gave our planet’s core the radioactive elements necessary to generate a magnetic field, a pair of Oxford geochemists say. The research, which is based on computer models, resolves two long-standing mysteries about Mother Nature's recipe for Earth. The first is why the planet has an abundance of the rare-earth metals samarium (Sm) and neodymium (Nd) compared meteorites, which are believed to be samples of Earth’s building blocks. The second riddle is how the planet’s metallic core has stayed hot enough over the eons to continue convection, a process that generates Earth’s protective magnetic shield.

Oxford University researchers Anke Wohlers and Bernard Wood got the idea to incorporate a sulfur-rich body like Mercury into Earth-formation computer simulations after making connections between colleagues’ previous studies relating rare earth elements, including samarium and neodymium, to sulfides; the elements’ chemical mismatch between Earth and meteorites; and observations from NASA’s MESSENGER spacecraft that Mercury has high levels of sulfur.

It's a theory that fits quite well with what's been studied on Earth, though it's not a perfect fit.

“That sort of roughly works, but there are all kinds of little questions that don’t quite work,” Wood said, “and one of them is, what is the energy source that drives the Earth’s magnetic field?”

The study, published in the journal Nature, offers insight into how Earth’s magnetic field – and, perhaps, the moon – came to be.

The models show the impacting body would have to have been 20 to 40 percent as big as Earth to produce the required chemical mix. The crash could have happened as the building blocks for Earth were melding together, or it could have been the hypothesized Mars-sized impactor, named Theia, that hit Earth and led to the formation of the moon.

With Jupiter on the move, the inner solar system was like a “mixing bowl,” Wood said.

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