Theia (planet)

Theia /θiːə/ is a hypothesized ancient planetary-mass object in the early Solar System that according to the giant impact hypothesis collided with the Early Earth around 4.533 billion years ago (BYa). According to the hypothesis, Theia was an Earth trojan about the size of Mars, with diameter of about 6,000 km (3,700 miles). New research by UCLA based on rock analysis sourced from Apollo missions 12, 15 and 17, suggests Theia collided head-on with Earth, in contrast to the previous theory which suggested a glancing impact. Models of the impact propose that Theia's debris gathered together around Earth to form the early Moon. After the debris from the collision flew into space, some scientists think that it originally formed two moons which later merged to form the single Moon we know today. However, the two-moon hypothesis is not necessary to explain the difference in the faces of the near and far sides of the Moon. The theory also explains why Earth's core is larger than would be expected for a body its size: according to the hypothesis, Theia's core and mantle mixed with Earth's.

Theia

In Greek mythology, Theia /ˈθiːə/ (sometimes rendered Thea, Théa or Thia), also called Euryphaessa "wide-shining", is a Titaness. The name Theia alone means simply "goddess" or "divine"; Theia Euryphaessa (Θεία Εὐρυφάεσσα) brings overtones of extent (εὐρύς, eurys, "wide", root: εὐρυ-/εὐρε-) and brightness (φάος, phaos, "light", root: φαεσ-). Her brother/consort is Hyperion, a Titan and god of the sun, and together they are the parents of Helios (the Sun), Selene (the Moon), and Eos (the Dawn).

Earlier myths

Hesiod's Theogony gives her an equally primal origin, a daughter of Gaia (Earth) and Uranus (Sky).Robert Graves also relates that later Theia is referred to as the cow-eyed Euryphaessa who gave birth to Helios in myths dating to Classical Antiquity.

Later myths

Once paired in later myths with her Titan brother Hyperion as her husband, "mild-eyed Euryphaessa, the far-shining one" of the Homeric Hymn to Helios, was said to be the mother of Helios (the Sun), Selene (the Moon), and Eos (the Dawn).

Planet

A planet (from Ancient Greek ἀστήρ πλανήτης astēr planētēs, or πλάνης ἀστήρ plánēs astēr, meaning "wandering star") is an astronomical object orbiting a star or stellar remnant that

The term planet is ancient, with ties to history, science, mythology, and religion. Several planets in the Solar System can be seen with the naked eye. These were regarded by many early cultures as divine, or as emissaries of deities. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. In 2006, the International Astronomical Union (IAU) officially adopted a resolution defining planets within the Solar System. This definition is controversial because it excludes many objects of planetary mass based on where or what they orbit. Although eight of the planetary bodies discovered before 1950 remain "planets" under the modern definition, some celestial bodies, such as Ceres, Pallas, Juno and Vesta (each an object in the solar asteroid belt), and Pluto (the first trans-Neptunian object discovered), that were once considered planets by the scientific community, are no longer viewed as such.