Iron: founding life

Shock waves similar to those due to the impacts of celestial bodies at the dawn of the Solar System were replicated by the “Z machine” in Albuquerque, New Mexico. The results show that, at the time of the formation of our planet, the vaporized iron was more abundant than previously thought in our days.
There was a time when the impacts of the solar system bodies in training were on the agenda. And more future planets grew, following precisely this uninterrupted succession of collisions, impacts became more violent. So violent – we are talking about more than 150 thousand km / h – to vaporize iron.


The Z-Machine installed at the Sandia National Laboratory. Photo by Randy Montoya

A process that is believed to be behind the formation of the iron core of the Earth and other celestial bodies. In many respects, however, it remains unclear. “One of the greatest difficulties,” says Richard Kraus of Harvard University, “is in the modeling of the iron during the impact, as in the planets iron is one of the main components, then its behavior is critical to understand how planets formed. In particular, still not well determined is the fraction of vaporized iron with collisions. ”
To seek an answer, Kraus and the coordinated team of researchers of LLNL (Lawrence Livermore National Laboratory) used the largest X-ray generator in the world, the Z Pulsed Power Facility – better known as the Z Machine – installed at Sandia National Laboratories in Albuquerque, New Mexico. With the “Z Machine”, and making use of a new technique capable of producing shock waves, they are thus able to measure a fundamental characteristic of the material: the entropic gain induced by shock compression. In other words, they were able to quantify the level of entropy produced by the impact, accordingly determining the conditions necessary to evaporate the iron present in the objects that collided with each other at the time of formation of the Earth.
The findings, published in the latest issue of Nature Geoscience, suggest that the impact pressure required to vaporize the iron is around 500 GPa, a value significantly lower than the previous theoretical estimate, which was nearly 900 GPa. This means that the iron vaporizes even with impacts at relatively low speeds, which implies a greater quantity of iron that has been vaporized during the infancy of the Earth. “This result forces us to rethink the processes that have led, for example, the formation of the Earth’s core. Not so much a collapse directed towards the heart of the Earth in the making of the iron present in the bodies that collided, then, as a vaporization of the iron itself as a result of the impact, resulting in the spread on the surface of the planet dominated by the vapor cloud.
A phenomenon so alienating, this drop of liquid iron that bathed from above the Earth, to be able to find it, it is hard to imagine. Yet the model developed by scientists of LLNL not only is consistent with the results produced by the test of Z machine, but would also explain, for example, the relative lack of siderophile elements in the crust and mantle of the moon: to make our satellite poor of these substances it would be necessary its inability to hold large amounts of iron vaporized coming from planetesimals, due to the fact that the escape velocity from the moon is much smaller than that of our planet.

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