Mercury (planet) Mercury (planet) Mercury is the smallest and innermost planet in the Solar System. Its orbital period around the Sun of 87.97 days is the shortest of all the planets in the Solar System. It is named after the Roman deity Mercury, the messenger of the gods. Like Venus, Mercury orbits the Sun within Earth's orbit as an "inferior planet", and never exceeds 28° away from the Sun. When viewed from Earth, this proximity to the Sun means the planet can only be seen near the western or eastern horizon during the early evening or early morning. At this time it
Planet Nine to an eccentric orbit. The in situ formation of a planet at this distance would require a very massive and extensive disk, or the outward drift of solids in a dissipating disk forming a narrow ring from which the planet accreted over a billion years. If a planet formed at such a great distance while the Sun was in its birth cluster, the probability of it remaining bound to the Sun in a highly eccentric orbit is roughly 10%. A previous article reported that a massive disk extending beyond 80 AU would drive Kozai oscillations, a periodic exchange between eccentricity