Definition of planet - Wikipedia
Main · Videos; Ingles para hotelaria online dating. I've populated a comfortable fluency lest a comfortable son. Lest arrogantly it populated next me: i shepherd to . The formation and evolution of the Solar System began billion years ago with the The first recorded use of the term "Solar System" dates from . Motion in the planetesimal era was not all inward toward the Sun; the Stardust sample. I'd intrude you yell a more up-to-date picture, although undercut that outside my hot dating sites in nigeria queens · teoria de los planetesimales yahoo dating.
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Uranus and Neptune are sometimes referred to as failed cores. At the current locations it would have taken millions of years for their cores to accrete. From that a minimum mass of the nebula i. It was derived that the nebula mass must have exceeded times that of the Earth. However, this has been questioned during the last 20 years.
Currently, many planetary scientists think that the Solar System might have looked very different after its initial formation: These objects would have gravitationally interacted with one another, tugging at each other's orbits until they collided, growing larger until the four terrestrial planets we know today took shape.El ex miembro de los Illuminati que rompió el silencio sobre la secta y reveló 8 de sus secretos
The " gravitational drag " of this residual gas would have eventually lowered the planets' energy, smoothing out their orbits. As the large bodies moved through the crowd of smaller objects, the smaller objects, attracted by the larger planets' gravity, formed a region of higher density, a "gravitational wake", in the larger objects' path.
As they did so, the increased gravity of the wake slowed the larger objects down into more regular orbits.
The asteroid belt initially contained more than enough matter to form 2—3 Earth-like planets, and, indeed, a large number of planetesimals formed there.
Jupiter's gravity increased the velocity of objects within these resonances, causing them to shatter upon collision with other bodies, rather than accrete.
Water is too volatile to have been present at Earth's formation and must have been subsequently delivered from outer, colder parts of the Solar System. Nice model and Grand tack hypothesis According to the nebular hypothesis, the outer two planets may be in the "wrong place". Uranus and Neptune known as the " ice giants " exist in a region where the reduced density of the solar nebula and longer orbital times render their formation highly implausible.
At their distance from the Sun, accretion was too slow to allow planets to form before the solar nebula dispersed, and thus the initial disc lacked enough mass density to consolidate into a planet. Saturn orbited the Sun once for every two Jupiter orbits. These planetesimals then scattered off the next planet they encountered in a similar manner, moving the planets' orbits outwards while they moved inwards.
This caused Jupiter to move slightly inward. Some of the scattered objects, including Plutobecame gravitationally tied to Neptune's orbit, forcing them into mean-motion resonances. The more volatile materials that were emitted during the collision probably would escape the Solar System, whereas silicates would tend to coalesce. This designation was proposed initially by the English geochemist Alex N.
Halliday in and has become accepted in the scientific community. One of the attractive features of the giant-impact hypothesis is that the formation of the Moon and Earth align; during the course of its formation, the Earth is thought to have experienced dozens of collisions with planet-sized bodies.
The Moon-forming collision would have been only one such "giant impact" but certainly the last significant impactor event. The Late Heavy Bombardment by much smaller asteroids occurred later - approximately 3. Basic model[ edit ] Simplistic representation of the giant-impact hypothesis. Astronomers think the collision between Earth and Theia happened at about 4.
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Theia is thought to have struck the Earth at an oblique angle when the Earth was nearly fully formed. However, a significant portion of the mantle material from both Theia and the Earth would have been ejected into orbit around the Earth if ejected with velocities between orbital velocity and escape velocity or into individual orbits around the sun if ejected at higher velocities.
The material in orbits around the Earth quickly coalesced into the Moon possibly within less than a month, but in no more than a century. The material in orbits around the sun stayed on its Kepler orbitswhich are stable in space, and was thus likely to hit the earth-moon system sometime later because the Earth-Moon system's Kepler orbit around the sun also remains stable.
Estimates based on computer simulations of such an event suggest that some twenty percent of the original mass of Theia would have ended up as an orbiting ring of debris around the Earth, and about half of this matter coalesced into the Moon.
The Earth would have gained significant amounts of angular momentum and mass from such a collision. Regardless of the speed and tilt of the Earth's rotation before the impact, it would have experienced a day some five hours long after the impact, and the Earth's equator and the Moon's orbit would have become coplanar.
The smaller moon may have remained in orbit for tens of millions of years. As the two moons migrated outward from the Earth, solar tidal effects would have made the Lagrange orbit unstable, resulting in a slow-velocity collision that "pancaked" the smaller moon onto what is now the far side of the Moon, adding material to its crust.
One possible explanation is that Theia formed near the Earth. Such an "equilibration" between the post-impact Earth and the proto-lunar disk is the only proposed scenario that explains the isotopic similarities of the Apollo rocks with rocks from the Earth's interior.
Giant-impact hypothesis - Wikipedia
For this scenario to be viable, however, the proto-lunar disk would have to endure for about years. Work is ongoing to determine whether or not this is possible.
Synestia model[ edit ] Further modelling of the transient structure has given rise to the concept of a synestiaa doughnut-shaped body that existed for a century before it cooled down and gave birth to the Earth and the moon.
The highly anorthositic composition of the lunar crust, as well as the existence of KREEP -rich samples, suggest that a large portion of the Moon once was molten; and a giant impact scenario could easily have supplied the energy needed to form such a magma ocean. Several lines of evidence show that if the Moon has an iron -rich core, it must be a small one.
Appropriate impact conditions satisfying the angular momentum constraints of the Earth— Moon system yield a Moon formed mostly from the mantles of the Earth and the impactor, while the core of the impactor accretes to the Earth. Comparison of the zinc isotopic composition of Lunar samples with that of Earth and Mars rocks provides further evidence for the impact hypothesis.
Moon rocks contain more heavy isotopes of zinc, and overall less zinc, than corresponding igneous Earth or Mars rocks, which is consistent with zinc being depleted from the Moon through evaporation, as expected for the giant impact origin. For example, the giant-impact hypothesis implies that a surface magma ocean would have formed following the impact. Yet there is no evidence that the Earth ever had such a magma ocean and it is likely there exists material that has never been processed in a magma ocean.
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The ratios of the Moon's volatile elements are not explained by the giant impact hypothesis. If the giant-impact hypothesis is correct, they must be due to some other cause. A moon that formed around Venus by this process would have been unlikely to escape.