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Rare metallic asteroids could have broken molten iron

  Rare metallic asteroids could have broken molten iron.
This diagram shows a theoretical phenomenon called Ferrovolcanism, in which metal-rich asteroids break down molten iron. Ferrovolcanism can occur when pockets of molten alloy rise to the surface and can explain the formation of meteorites called pallasites. An upcoming NASA space mission to the Asteroid Psyche could allow scientists to validate their theory. (James Tuttle Keane (Caltech), Alexandria Johnson.) Photo credit: Purdue University

The metallic asteroid psyche has puzzled scientists because, given its iron-nickel composition, it is less dense than it should be. Now, a new theory could explain psyches low density and metallic surface.

Unlike most asteroids, the psyche seems to consist mostly of iron and nickel rather than rubble. It is believed that metal-rich asteroids formed when original planetsimals collided, scraping off much of the outer material, leaving behind the inner metal cores, which then cooled and solidified from the outside to the inside. During this cooling process, an alloy of molten residual pockets of iron, nickel, and lighter elements such as sulfur may have flowed to the surface through liquid-filled cracks called dikes, covering a topmost rocky layer.

"We refer to these processes collectively as & # 39; ferro-volcanism & # 39 ;," said Brandon C. Johnson, associate professor of geospatial and atmospheric science at Purdue University.

The theory is described in a research report published in the journal Nature Astronomy Monday (September 1

6). The paper was co-written by Johnson; Michael M. Sori, Associate Staff Scientist at the University of Arizona Lunar and Planetary Laboratory; and Alexander J. Evans, Assistant Professor of Earth, Environmental, and Planetary Sciences at Brown University.

It is believed that meteorites, so-called pallasites, are a mixture of core and shell material that may be mixed together by ferrovolcanism. The sulfur-mixed pockets of liquid metal are less dense than the surrounding solid material and create an "overpressure" that may possibly cause the spreading of dykes and allow the occurrence of ferrovolcanism.

The researchers determined how far these dikes would need to propagate in order to facilitate volcanism.

"Our calculations suggest that ferro-volcanic eruptions are possible for small, metal-rich bodies, especially for sulphurous melts and bodies with coats thinner than about 35 kilometers, or for bodies where the coat was localized by large ones Impact crater, "Johnson said.

An upcoming NASA space mission to Psyche will help scientists test this theory. The ferro-volcanic eruptions may explain the low density of psyche that exists despite radar and other scientific evidence of metallic surface composition. Psyche, the largest known metallic asteroid in the solar system, is located in the asteroid belt between Mars and Jupiter. Its density is estimated at only about half that of an iron meteorite.

The researchers predict that the asteroid could consist of two layers in which a metal core is surrounded by a sheath of rockier material of lesser density.

"Ferrovolcanism It may have transported nuclear material to the surface and caused radar detections of metal there," Johnson said.

The research is still in progress. Future work will use more complex models to study the occurrence of ferrovolcanism and possibly to study the evolution of psyche.

] No spaceship has yet visited a metallic asteroid, and the concept of ferrovolcanism is based on mathematical models. NASA plans to launch the spacecraft in 2022. The mission could allow scientists to validate the theory and answer questions about the role of metallic asteroids in the evolution of the solar system.

Iron volcanoes may have broken out on metal asteroids

Further information:
Ferrovolcanism on Metal Worlds and the Origin of Pallasites, Nature Astronomy (2019). DOI: 10.1038 / s41550-019-0885-x, https://nature.com/articles/s41550-019-0885-x

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Purdue University

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