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 orbits of extreme trans-Neptunian objects was first described by Trujillo and Sheppard, who noted similarities between the orbits of Sedna and . Without the presence of Planet Nine, these orbits should be distributed randomly, without preference for any direction. Upon further analysis, Trujillo and Sheppard observed that the arguments of perihelion of 12 eTNOs with perihelia greater than and semi-major axes greater than were clustered near zero degrees, meaning that they rise through the ecliptic when they are closest to the sun. Trujillo and Sheppard proposed that this alignment was caused by a massive unknown planet beyond Neptune via the