麻豆社

Professor Mark聽McCaughrean explains how two space crafts sent to mysterious Mercury will help solve some questions about planets were formed in the solar-system.

"Mercury is this mysterious little planet 40% the size of the Earth and closest to the Sun, mostly made of iron" he says.

"It is actually easier to get to the outer solar-system than it is to get to Mercury... the Sun's gravitational pull makes it hard for probes to slow down".

(Image: Mercury; Credit: Getty Images)