Mercury is the innermost and smallest planet of the Solar System. Because it has almost no atmosphere to retain heat, Mercury’s surface experiences the greatest temperature variation of all the planets.

Observation

Mercury appears as a morning or evening star from Earth, but due to it’s proximity to Sun, it is very hard to see. Still, Mercury can be observed at least twice a year: in spring at dusk and in autumn before dawn.

Structure

Crust

The crust is similar in appearance to the that of the Moon with mare-like plains and heavy cratering. A distinctive feature of the surface crust is the presence of numerous narrow ridges, which might have formed as Mercury’s core and mantle cooled and contracted after the crust had solidified.

Core

Mercury’s extreme high density infers that the planet has a large, iron-rich core, with higher iron content than that of any other major planet in the Solar System.