The idea of a metal asteroid spewing molten iron as it hurls though the infinite voids of space may seem the stuff of science fiction. This, however, is the basic concept of ferrovolcanism — a new type of planetary activity proposed recently by NASA. And NASA has announced its intention to send a probe to the metal asteroid Psyche in 2022 to search for evidence of such extraterrestrial volcanic activity.
Jacob Abrahams of the University of California has described new research as “the first time anyone has worked out what volcanism is likely to look like on these asteroids.”
Metal asteroids are thought to be the exposed iron-rich cores of planetesimals that suffered a catastrophic collision as the solar system was developing, before they could grow into full-sized planets.
The naked core would have been exposed to cold space while still molten.
And the asteroid would have cooled and solidified from the outside in, forming a solid iron crust denser than the underlying molten iron, believes Mr Abrahams.
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That kind of density mismatch is part of what can create volcanoes on Earth — lighter, more buoyant material rising up through cracks in the crust — and could have led to iron-spewing volcanoes on metal asteroids as the objects cooled long ago.
Another way that ferrovolcanism could have occurred on metal asteroids was described by planetary scientist Brandon Johnson of Brown University in Providence, R.I.
If a cooling iron core also contained a little bit of rock and sulphur, he theorises, the core could have been cocooned beneath a rocky, not iron, crust.
As the core cooled further, pockets of iron-rich liquid with extra sulphur dissolved in them would have hardened more slowly than surrounding materials.
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Those pockets would be more buoyant than the rock above them, so they’d force their way up and out, Johnson says.
If Psyche has such a rocky veneer over iron, that could explain why the asteroid appears much less dense than expected, Johnson says.
“We kept thinking, ‘It’s too wild, it can’t be right,’ ” says Professor Brandon Johnson of Brown University, of the idea of ferrovolcanism.
“But we couldn’t prove to ourselves that it wouldn’t work. Because another group came up with the same idea at the same time, it cannot be too wild.”
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The Psyche spacecraft can look for signs of past ferrovolcanism when it arrives at the asteroid, located in the main asteroid belt between Mars and Jupiter, in 2026, says mission principal investigator Professor Lindy Elkins-Tanton, of Arizona State University in Tempe.
Additionally, if Psyche were rotating while it cooled, its molten core could have generated a magnetic field.
Volcanic flows that cooled on the asteroid’s surface would have recorded evidence of that magnetic field.
“We might actually be able to see these things,” says Professor Elkins-Tanton. “I think it’s really cool.”
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