Theia (planet) - Wikipedia
Planet hypothesized to have impacted Earth and created the Moon An artist's depiction of the hypothetical impact of a planet like Theia and the Earth Theia ( / ˈ θ iː ə / ) is a hypothesized ancient planet in the early Solar System which, according to the giant-impact hypothesis , collided with the early Earth around 4.5 billion years ago, with some of the resulting ejected debris coalescing to form the Moon . [1] [2] Collision simulations support the idea that the large low-shear-velocity provinces in the lower mantle may be remnants of Theia. [3] [4] Theia is hypothesized to have been about the size of Mars , and may have formed in the outer Solar System and provided much of Earth's water , though this is debated. [5] In Greek mythology , Theia was one of the Titans , the sister of Hyperion whom she later married, and the mother of Helios the sun god, and Selene , the goddess of the Moon, [6] a story that parallels the planet Theia's theorized role in creating the Moon. [7] Theia is hypothesized to have orbited in the L 4 or L 5 configuration presented by the Earth–Sun system, where it would tend to remain. If this were the case it might have grown to a size comparable to Mars , with a diameter of about 6,102 kilometres (3,792 miles). [ citation needed ] Gravitational perturbations by Venus could have put it onto a collision course with the early Earth. [8] Animation of collision between Earth (blue) and Theia (black), forming the Moon (red and gray). Bodies are not to scale. According to the giant impact hypothesis , Theia orbited the Sun , nearly along the orbit of the proto-Earth , by staying close to one or the other of the Sun-Earth system's two more stable Lagrangian points ( i.e. , either L 4 or L 5 ). [8] Theia was eventually perturbed away from that relationship by the gravitational influence of Jupiter , Venus , or both, resulting in a collision between Theia and Earth. [ citation needed ] Initially, the hypothesis supposed that Theia had struck Earth with a glancing blow [9] and ejected many pieces of both the proto-Earth and Theia, those pieces either forming one body that became the Moon or forming two moons that eventually merged to form the Moon. [10] [11] Such accounts assumed that a head-on impact would have destroyed both planets, creating a short-lived second asteroid belt between the orbits of Venus and Mars. In contrast, evidence published in January 2016 suggests that the impact was indeed a head-on collision and that Theia's remains are on Earth and the Moon. [12] [13] [14] From the beginning of modern astronomy, there have been at least four hypotheses for the origin of the Moon: A single body split into Earth and Moon The Moon was captured by Earth's gravity (as most of the outer planets ' smaller moons were captured) The Earth and Moon formed at the same time when the protoplanetary disk accreted The Theia-impact scenario described above The lunar rock samples retrieved by Apollo astronauts were found to be very simila
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