A large chunk of Mercury may have been blown away by the sun

By Jonathan O’Callaghan

TIM BROWN / SCIENCE PHOTO LIBRARY

A giant impact four billion years ago could have resulted in Mercury losing most of its mantle to deep space, potentially explaining one of the planet’s key mysteries.

Mercury is unusual compared to other rocky planets in the solar system as its iron core accounts for more than 80 percent of its radius, compared to just 50 percent for Earth. This makes it very dense with just a thin mantle, about 500 kilometres thick, above the core. Astronomers have long wondered why, with no clear answer.

Now, …