Mercury is the innermost and smallest planet of the Solar System. Because it has almost no atmosphere to retain heat, Mercuryâ€™s surface experiences the greatest temperature variation of all the planets.
Mercury appears as aÂ morning or evening star from Earth, but due to itâ€™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.
|Crust||Surface of silicate rock|
|Mantle||Solid silicate rock|
The crust is similar in appearance to the that of the Moon with mare-like plains and heavy cratering. AÂ distinctive feature of the surface crust is the presence of numerous narrow ridges, which might have formed as Mercuryâ€™s core and mantle cooled and contracted after the crust had solidified.
Mercuryâ€™s extreme high density infers that the planet has aÂ large, iron-rich core, with higher iron content than that of any other major planet in the Solar System.