Mercury is the smallest planet and the closest to the Sun — a sun-blasted ball of rock and iron with almost no air, extremes of heat and cold like nowhere else, and the fastest orbit of any world in the Solar System.
With almost no atmosphere to hold heat, Mercury swings between 427°C in direct sun and −173°C in shadow — the largest temperature swing of any planet. Ice may even survive in permanently shadowed craters at its poles, just kilometres from the hottest sunlit ground.
Mercury orbits the Sun in just 88 days, but spins so slowly that a single solar day lasts 176 Earth days — meaning a year passes in half a day. Stand on its surface and the Sun would appear three times larger than from Earth.
Mercury is the second-densest planet. Its enormous iron core fills about 85% of its radius, wrapped in a thin rocky shell scarred by billions of years of impacts. The huge Caloris Basin crater stretches 1,550 km — wide enough to hold France.
“The first step out from the Sun — small, fierce, and impossibly fast.”
— CEO GALILEO