Scientists believe that metal asteroids floating through space could have spewed molten iron from their cores in enormous volcanic eruptions.
New research by planetary scientists at the University of California Santa Cruz, prompted by a NASA mission to launch a probe to a metallic asteroid, discovered the volcanoes.
The NASA mission will examine an asteroid called Psyche, the largest metallic asteroid in our solar system.
Professor Francis Nimmo said that one of his graduate students, Jacob Abrahams, developed simple models of how the asteroids cooled and solidified in space.
“One day he turned to me and said, ‘I think these things are going to erupt,'” Prof 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.”
The pair’s findings have been set out in a paper to be published in the journal Geophysical Research Letters.
They note how metallic asteroids originated early in the history of the solar system when planets were first beginning to form.
When protoplanet or “planetesimal” bodies were involved in catastrophic collisions, they could be stripped of their rocky outer layers, exposing their molten, iron-rich core.
Floating through the sub-zero cold of space, this blog of molten metal would quickly begin to cool and solidify.
“In some cases it would crystallise from the centre out and wouldn’t have volcanism, but some would crystallise from the top down, so you’d get a solid sheet of metal on the surface with liquid metal underneath,” Prof Nimmo said.
Dr Abrahams said that if the asteroid was mostly composed of pure iron, then it would be runnier than “the thick, viscous lava flows you see on Hawaii”.
“At the other extreme, if there are light elements mixed in and gases that expand rapidly, you could have explosive volcanism that might leave pits in the surface.”
NASA is set to launch its probe to Psyche in 2022, and it will reach the asteroid in 2026, when scientists will look for evidence of volcanism.
Unfortunately for the researchers, because metallic asteroids would have solidified quickly after their formation – and because there has now been billions of years since their formation – any evidence on the asteroid’s surface could have been degraded away.
“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,” Prof 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.”