Terrestrial planet Terrestrial planet A terrestrial planet, telluric planet, or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun, i.e. Mercury, Venus, Earth, and Mars. The terms "terrestrial planet" and "telluric planet" are derived from Latin words for Earth ("Terra" and "Tellus"), as these planets are, in terms of structure, "Earth-like". Terrestrial planets have a solid planetary surface, making them substantially different from the larger giant planets, which are composed mostly of some combination of hydrogen, helium, and water existing in various
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