Mercury and chaos of the solar system: a shock hypothesis
Mercury in 2011 (false colors) © NASA/JHU Applied Physics Lab/Carnegie INST. Washington
The formation of the planets of the solar system is today well understood as a whole, explained by theaccretion of the residual material around the young star – the sun -, which was formed by gravitational collapse of the initial nebula. There are nevertheless a few gray areas: the gaseous planets (Jupiter, Saturn, Uranus, Neptune) so formed by gravitational collapse? And, for what occupies us today, why is Mercury so different from other rocky stars (Venus, Earth and Mars)?
Mercury is the smallest planet in the solar system – Titan, a natural satellite of Saturn, even has a 6 % larger diameter -, but that is not its smallest quirk. It is closest to the sun, but also the most eccentric, that is to say that its orbit leads it to move away from the star a lot and to get a lot closer to it.
Its composition also intrigues: it is made up of approximately 70 % iron and its ferrous nucleus is just very surprising. It occupies about 85 % of its radius for 45 to 60 % of its volume! As a comparison, that of the earth is only 17 % of its volume.
Moon/Mercury comparison and view of the exceptionally large nucleus of mercury. © Vito Technology, inc. Starwalk
A collision with a planet of the same mass that Mercury would explain its characteristics
Illustration of a collision between two planets comparable to Mercury in terms of size and mass. © generated on Grok by Brice Haziza
In a Study based on computer simulationsa team from the National Observatory of Brazil has just shown that the best scenario to reproduce current mercury is not the collision with a small wandering planet as supposed, but a cataclysmic shock with a planet of the same size as it is!
Scientists developed this hypothesis by taking into account that the meetings between objects of the same size were very common in the original chaos of the solar system: around 30 % of collisions.
The researchers set up a “proto mercury” of approximately 0.13 % of the land mass with an iron composition of 30 %. They then simulated collisions with variable mass and iron content objects. The choice of the angle of impact and the exhaust speed of the planets is then a crucial parameter to achieve the composition of mercury as we know it.
The best results were obtained after three types of simulations with different angles of impacts, succeeding in producing a planet of 95 % of the mass of mercury and an iron heart stack in the right value of values.
The European Bepicolombo (ESA) probe is precisely orbit around Mercury to try to learn more about this strange little dense planet.
The Mercury planet overflown by Bepicolombo. © ESA/BEPICOLOMBO/MTM
