Mercury

Mercury is the first planet from the Sun. It is the smallest planet in the Solar System, being only just shy of more than 3000 miles in diameter. In fact, Ganymede, the largest moon in the Solar System, and of Jupiter, is larger than this planet. Mercury has an extremely thin atmosphere. So thin, in fact, there is only just more than one metric ton of air in the atmosphere (see more in Atmosphere). Mercury has the largest temperature range of any planet in the Solar System. Its day temperature can reach more than 800 degrees Fahrenheit and less than -290 degrees Fahrenheit. Mercury can make one orbit in eighty-eight Earthen days. Around it are the man-made satellites, MESSENGER and Mariner 10.

Formation
The gas giants of the Solar System became gaseous, because they had less accretion acting on the gases that created the planet. Instead, because the rocky planets, including Mercury, were closer to the Sun, the nebula accreted faster. Since the heat was so intense near the Sun, the planet dried up like a raisin and shrunk to the size that we know of today. This is different from the other cases of the formation of different celestial bodies in the Solar System, including the other rocky planets.

Atmosphere
As you saw in the introduction, Mercury only has 2200 pounds of atmosphere. It is made up of about forty percent oxygen, about twenty percent sodium, about twenty two percent hydrogen, and about ten percent helium. The last one percent is made up of trace gases. The atmosphere of Mercury is produced from the heat within the planet.

Surface
The surface of Mercury is heavily cratered. The best known of these craters is the Caloris Basin, which is about one thousand miles in width. Ancient volcanoes show signs that volcanism was once present on this planet. The rest of the surface include cliffs and plains that became solid, which is a process called solidification. This solidification created these volcanoes.

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Structure
The core is thought to consist of iron, which happened due to the amount of accretion the nebula received when it created the Solar System. Around that is a silicate mantle, where the convection currents occur, shifting tectonic plates. The last is the crust, which suffers from asteroid impacts and volcanism.

Observation
Mercury can be easily seen during twilight or just after the sunset. The visibility cannot remain for long due to its speedy orbit around the Sun. The elongation, or the point at which a celestial object is at its farthest point from a solar remnant, of Mercury from the Sun is the best time to view it, though this event only occurs seven times a year.