Science on the Ground Gives Clues to Planetary Formation

Astronomy is a science that is always associated with the sky, and rightly so.  But since the beginning of modern science there have been discoveries made on Earth that teach us about the formation and evolution of the Universe.  As telescopes become more powerful and allow us to look deeper into space, the technology to simulate outer-space conditions here on Earth has grown significantly.  In Albuquerque, New Mexico, a powerful tool called the Z machine generates quick high-energy pulses of electricity, which can be used to generate X-rays and Gamma rays to be used in experiments.

Credit: Randy Montoya

Outside of astronomy, the Z machine has been used to test the effects of nuclear blasts on a variety of materials.  But when astronomers use such a high energy simulator, it determines the conditions inside a star, or at the epicentre of a collision of two large rocky bodies.

A team from UC Davis has used the Z machine to give insights into the formation of the Earth and Moon.  The leading theory in the Moon’s formation is that 4.5 billion years ago during the formation of the solar system, a Mars-sized chunk of rock smashed into the younger, larger Earth, blasting out material that was pulled together by gravity to form our Moon.

The team, led by Sarah Stewart, UC Davis professor of Earth and Planetary Sciences, used the Z machine to subject Iron to high shock pressures by slamming Aluminum plates into the samples at high speeds.  Using this method they were able to determine the critical impact conditions needed to vaporize the Iron.

They determined that the shock pressure needed to vaporize the Iron was much lower than expected.  This would mean that more Iron was vaporized during the Earth’s formation than was previously thought.  This Iron vapour would spread out during collisions in the early solar system, mixing with the Earth’s mantle, whereas solid chunks of Iron would be heavier and sink toward the core.

This process could also explain why the Moon lacks Iron-rich material despite being exposed to similar extreme conditions.  The Iron vapour could have flown away from the Moon and been pulled toward the Earth’s stronger gravity, before condensing and falling onto the Earth.

“The timing of Earth’s core formation can only be determined via chemical signatures in Earth’s mantle, a technique that requires assumptions about how well the iron is mixed. This new information actually changes our estimates for the timing of when Earth’s core was formed,” says Lawrence Livermore National Laboratory scientist Richard Kraus, co-author of the study.

This is the essence of Science.  We have good theories in place that the evidence leads us to, and then something changes, so we update our theories, and come up with updates models to fit what we find.  As we are able to build better machines to test the conditions of the energetic past, we will continue to probe deeper into the secrets of the Universe.

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