Mercury is the smallest of the 8 planets in the solar system. Its orbit has the highest eccentricity, meaning that its orbit is more elliptical than circular. Its farthest point from the sun (aphelion) is about 1.5 times as far as its closest point (perihelion), giving it an eccentricity of 1.5 (a perfectly circular orbit would have an eccentricity of 1.0). Mercury also lacks an atmosphere, and, as evidenced by the abundant craters covering its surface, appears to have been geologically inactive for billions of years. Another strange trait of Mercury is that it has a surprisingly high density given its tiny size. This has led scientists to infer that it has a much higher iron content than the other rocky planets. These are just a few attributes that set Mercury apart from the other inner planets.

Mercury differs from Venus, Earth, and Mars because it is made up of 70 % metals(mainly iron) and 30 % rock. The other planets are 35 % metal and 65% rock.

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The main difference between Mercury and the other inner planets is that Mercury has very little atmosphere, which means it doesn't have as much weather or wind as the other inner planets do.

Mercury is the smallest of the four inner planets and has the thinnest atmosphere, in part because it is also the closest to the sun. Being small, Mercury has also been geologically dead for longer - Martian volcanoes have erupted in the last hundred million years, and Earth and Venus have active volcanic activity. Lastly, Mercury's orbit is much more elliptical than the other inner planets.