Explaining the Mystery of Mercury's Origin
For probably as long as humans have been able to look up and see other planets, we have been wondering how the planets came to be. For Venus and Earth it is generally accepted that they formed as the result of smaller objects colliding and coalescing into the planets we know today, but what about Mercury? The nearest planet to the Sun has some curious properties to it, including a very high concentration of iron, and now researchers at Arizona State University have an explanation for why.
Of the terrestrial planets in the Solar System, Mercury has the greatest concentration of metallic iron, with 65% of its mass being its iron core, compared to Earth's core making up 32% of its total mass. Also Mercury has a great many volatiles on it, such as water, lead, and sulfur, even compared to the Moon. This is particularly confusing as it indicates that the planet likely did not suffer a giant impact in the past, even though such an event would explain its lack of a mantle. The Arizona researchers though suggest that while Mercury never suffered a giant impact, like Earth and Venus did, it likely suffered many smaller, glancing impacts, which stripped off its core little by little.
The idea of glancing impacts is not new, but had always been discounted before, as the belief was that the object would be caught gravitationally, and ultimate be devoured by the larger body; proto-Venus or proto-Earth. According to the new theory and model though, glancing blows do not necessarily doom a body, and multiple could actually help preserve the dominate survivor of these impacts.
Source: Arizona State University