Researchers have a new hypothesis about how metallic asteroids formed. Originating as blobs of molten iron floating in space, scientists now think that as the blobs became solid, volcanoes spurted liquid iron through their crust to form a solid iron crust.
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This theory was developed by scientists at UC Santa Cruz who were prompted to do the research in part by NASA’s plans to send a probe to Psyche, the largest metallic asteroid in the solar system.
Professor of Earth and planetary sciences, Francis Nimmo, said the NASA mission sparked his interest so had graduate student Jacob Abrahams begin to develop some models of how the asteroids cooled and solidified.
It's going to blow!
"One day he turned to me and said, 'I think these things are going to erupt,'" Nimmo said. "I'd never thought about it before, but it makes sense because you have a buoyant liquid beneath a dense crust, so the liquid wants to come up to the top."
While the idea seems almost too Hollywood to be real Nimmo says it makes sense and the subsequent investigations into how metallic asteroids form has been accepted as a research paper for publication in Geophysical Research Letters.
Collision strips asteroid of the rocky surface
The history of metallic asteroids goes back to the early stages of the solar system's formation when planets were beginning to form. It is thought that if a protoplanet or "planetesimal" was involved in a massive collision, it could be stripped of its rocky outer layers, leaving just its molten, iron-rich core.
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This hot melty blob once exposed to the cold of space would begin to cool and solidify.
"In some cases, it would crystallize from the center out and wouldn't have volcanism, but some would crystallize from the top down, so you'd get a solid sheet of metal on the surface with liquid metal underneath," Nimmo said.
Psyche mission will look for volcanoes
NASA's Psyche mission is set to launch in 2022, reaching the asteroid four years later. The mission will look for signs of volcanism to help support Nimmo and Abraham's theory.
Proof of iron volcanoes might look like variations in the color or composition of the material on the asteroid's surface, or as apparent as volcano-like vents. Abraham says it's unlikely they will find mountainous volcanoes like the ones we are accustomed to on Earth.
However not finding visual evidence won't’ disprove the idea. Because the eruption happened so long ago, surface evidence of the volcanoes might be long gone.
Another method to test the theory will be to investigate iron meteorites already in collections on Earth.
"There are lots of these metallic meteorites, and now that we know what we're looking for, we might find evidence of volcanism in them," Nimmo said.
"If material got erupted onto the surface, it would cool very fast, which would be reflected in the composition of the meteorite. And it might have holes in it left by escaping gas."
Interestingly when the Santa Cruz team presented their findings at a recent academic conference, they met another group of researchers who had reached a similar conclusion giving some good backing to their hypothesis.