Final answer:
Mercury is believed to have a high proportion of iron primarily because of its high density and the presence of a weak magnetic field, suggesting a large, partly liquid iron core. Giant impacts during Mercury's formation may have stripped away much of its silicate mantle, and solar heat could have evaporated lighter elements, further increasing its iron relative to silicates.
Step-by-step explanation:
Scientists believe that Mercury has a high proportion of iron for several reasons. First, Mercury's high density indicates it is made largely of heavy materials such as metals, the most prominent being iron. Models suggest that Mercury has a substantial metallic iron-nickel core that makes up about 60% of its mass. Second, Mercury's weak magnetic field supports the presence of a large metal core. This is because a magnetic field generally requires liquid movement inside the core, inferring that part of Mercury's core is liquid iron.
The giant impact hypothesis further explains how Mercury could have such a high iron content compared to other rocky planets. According to this hypothesis, Mercury might have suffered several massive collisions that stripped away much of its silicate mantle, leaving behind a body with an iron-dominated composition. Additionally, evaporation of volatile materials by solar heat during Mercury’s formation could account for the loss of lighter silicates, augmenting the relative iron abundance.