Mercury
Mercury is the closest planet to our star, the Sun, but also the smallest of our Solar System. It is a terrestrial planet type (ie with a rocky surface, and an internal structure with different concentric layers) and it has no natural satellite. It is a planet difficult to observe since very close to the Sun, it appears only shortly after sunset or before sunrise.
Mercury has virtually no atmosphere because of heat reigning on its surface and the low gravity of the planet. This thin atmosphere is composed mainly of potassium (31%), sodium (25%) and oxygen (9.5%).
Due to its proximity to the Sun, Mercury is a very hot planet, with an average surface temperature of 179 ° C, but it can range from -183 ° C to the side in the shade, at 427 ° C for the light side. On the surface, the Sun appears 4 times larger than Earth, and its light is 8.9 times more intense.
Mercury's surface is covered with craters, and so closely resembles in appearance to the Moon, our natural satellite. These craters are ancient and tell the history of our Solar System when he was just born and the planetesimals collided with the planets to merge with them. These craters have remained intact because the planet has no internal activity a priori, which leaves no chance to the surface to renew.
Mercury has a relatively large metal core (volume occupies 42% of global volume, against 17% for the Earth) and as regards its internal composition, the planet is made of 70% metals (mainly located in the nuclei) and 30% silicate (coat). Proportionally, Mercury is the planet of the Solar System that has a quantity of iron twice as important as any other object in our solar system, which earned him the nickname "Metal planet."
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