Mercury is the closest planet to the sun. A dry, rocky, cratered world, it feels the full force of the sun's heat during the day, but, with only the barest of atmospheres, experiences freezing cold nights. It is difficult to study from Earth and largely unexplored.

structure and atmosphere

Below mercury's silicate rock surface is a solid rocky mantle about 340 miles (550 km) thick. This layer would have been liquid when mercury was young, and the source of volcanic eruptions.


Mercury is extremely dense compared with the other rocky planets, which signifies it is rich in iron. Its huge iron core is about 2,235 miles (3,600 km) in diameter. Surrounding the core is a rocky, silicate mantle and crust.

crust of silicate rock rocky, silicate mantle crust of silicate rock rocky, silicate mantle

iron core oxygen (52%) I

iron core

The mantle has now cooled and solidified, and during the past billion years volcanic eruptions have ceased. Below the mantle is a large iron core, formed when heavy iron sank within the young planet. The core is believed to be solid, but a thin layer of its outermost part could still be molten.

elements from mercury's surface, such as sodium, along with helium from the solar wind, form a very thin atmosphere. This is temporary and needs to be continuously replenished, because mercury's gravitational pull cannot hold on to the gases.

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