How Collisions Between Similar Masses Might Illuminate Mercury’s Formation

The mystery of Mercury’s formation has puzzled scientists for years. As the closest planet to the Sun, Mercury has a surprisingly large metallic core, making up about 70% of its mass, while its rocky mantle is much smaller. Previously, the leading theory suggested that a huge collision with another celestial body stripped away much of Mercury’s crust and mantle. However, new research indicates that this kind of impact is quite rare.

A fresh study presents a different idea, suggesting that Mercury may have formed from a near-collision between bodies of similar masses. This research, led by astronomer Patrick Franco, is detailed in the journal Nature Astronomy.

Franco explains, “Our simulation shows that we don’t need extraordinary impacts to explain Mercury’s features. A grazing collision between two protoplanets can account for its unique composition.” This scenario reflects a more common event in the early solar system when smaller rocky bodies were forming and interacting closely.

The study used a technique called “smoothed particle hydrodynamics” (SPH) to model this potential impact. SPH helps simulate how gases, liquids, and solids behave during motion and collision. Franco emphasizes that their model accurately reproduces both Mercury’s mass and its unusual metal-to-silicate ratio with less than 5% error. This research not only clarifies why Mercury has a small rocky layer compared to its large core but also suggests that the collision could have stripped away as much as 60% of its original mantle, explaining its current metallic composition.

Additionally, this new model offers insight into where any ejected material during the collision might have gone. Franco suggests that if the impact happened near other forming planets, some of the material could have ended up with another planet, perhaps Venus. He asserts, “This is a hypothesis worth exploring further.”

Understanding how Mercury was formed could also shed light on the creation of other rocky planets in our solar system. With new missions, like BepiColombo, aiming to gather more data about Mercury, researchers are eager to compare findings with geochemical evidence from meteorites and samples from the planet.

As Franco notes, “Mercury is the least explored planet in our system, but that’s changing quickly. Many discoveries are on the horizon.” This study contributes not only to our knowledge of Mercury but also to the broader understanding of planetary development in our solar system.

For more in-depth information, you can refer to the original research by Franco et al., published in Nature Astronomy.

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