Mercury: "Grazing collision" to explain unusual structure
The innermost planet in the solar system has an unusually high iron content, but no explanation has yet been found. Now there is a new theory
Image of Mercury taken by NASA's Messenger probe
(Image: NASA)
Mercury could have been formed in a collision between two similarly sized celestial bodies, giving it its unusually high metal content. This is the result of simulations by an international research team, which have now been presented by the SĂŁo Paulo Research Foundation in Brazil.
According to the study, a grazing collision between two celestial bodies is not only much more common; it could also better explain the peculiarities of the innermost planet than the most widely accepted hypothesis to date. This assumes a catastrophic collision between two celestial bodies of different sizes that left little more than the metal-containing core. However, even the new theory does not conclusively clarify where the lost material ended up.
Mercury's formation as a great mystery
Simulations have shown that collisions between celestial bodies of significantly different sizes are extremely rare, the research team now explains. Instead, it was much more common in the early solar system for two similarly sized celestial bodies to graze each other and then merge. This scenario is also much more plausible for the early history of Mercury, as the new simulations have shown. This would also have occurred comparatively late in the evolutionary history of the solar system, “when rocky planets of similar size would have competed for space in the inner regions around our star,” explains research leader Patrick Franco from the Institute of Geophysics in Paris.
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How Mercury formed and how it came to have such an unusually high metal content is an unsolved mystery, the research group explains. The highly ferrous core accounts for 70 percent of its mass. The theory of a huge impact that knocked out large parts of the mantle was also unsatisfactory until now. This is because it was not clear where the material would have ended up. Most of it would simply have had to hit the young Mercury again afterwards. In a grazing collision, on the other hand, parts of the material would be knocked out and not fall back to Mercury, the team writes. Where it ultimately ended up, however, still needs to be investigated. The research work has been published in the journal Nature Astronomy.
(mho)
