Construction of planets from protoplanetary disks

Planet formation from protoplanetary disks

An artist’s perception of the early solar nebulae illustrating material in the disk as it cools and melts together, eventually evolving into rocky planets. The composition of the rocky planets and meteorites of the solar system differs from that of the Sun, a jigsaw puzzle in that both come from the same molecular cloud material. Astronomers have simulated the complex temperature evolution of the young planetary disk and conclude that the solar nebula appears to have evolved under rare conditions, either formed from a parent molecular core with unusually high temperatures or with another energy source heating the young disk. Credit: USRA / LPI

Planets and their stars are formed from the same reservoir of nebulous material, and their chemical composition should therefore be correlated, but the observed compositions of planets do not quite agree with their central stars. In our solar system, for example, all rocky planets and planetesimals contain near-solar ratios of refractory elements (elements such as aluminum that condense from a gas when the temperature drops below 1500 kelvin) but are depleted of volatile elements (those, which evaporates) easily, like nitrogen). Astronomers believe that this was the result of planets formed by the fusion of already condensed mineral dust.

As the initial cold molecular clouds collapse and a slice forms, heating from the new star (plus the viscosity of the slice) can evaporate some of the original condensed material – forcing the condensation sequence to begin again, but now at higher temperatures and pressures. conditions that develop relatively rapidly. Astronomers also analyze meteorites of various types to determine their chemical composition. Depending on the properties of the original molecular clouds and disk, the temperatures produced during planetary formation may not have been sufficient to vaporize the most refractory of the pre-existing material. Since different minerals in planetesimals condense under different conditions, times and places, the overall situation is complex, making it difficult to understand the observed chemistry of planets.

CfA geologist Michail Petaev and his colleagues simulated the collapse of a molecular cloud and the formation of the star, disk, and planets, and analyzed the evolving distribution of temperatures across the disk to deduce the mineral condensation sequence. They find that the properties of the original clouds significantly affect the maximum temperatures reached in the disk and the resulting compositions of the planets and asteroids; the maximum temperature occurs around the end of the collapse phase, after a few hundred thousand years. They also find that while the composition of the star is similar to the composition of the molecular clouds, the star may be easily depleted in some of the most refractory elements – and therefore the star composition may not be a good approximation to the original composition of the nucleus. . Only cloud cores with high initial temperatures (or low discretion) will produce refractory planets. It is essential that they conclude that in order to reproduce the composition seen in the meteorites of the solar system and the terrestrial planets, either the original core had rare properties such as temperatures close to 2000 kelvin (well above the expected median value of 1250 kelvin), or another source of heating must have raised the temperature of the protoplanetary disk.

The study was published in Monthly announcements from the Royal Astronomical Society.


The planet does not fall far from the star


More information:
Min Li et al, Maximum temperatures in evolving protoplanetary disks and composition of planetary building blocks, Monthly announcements from the Royal Astronomical Society (2021). DOI: 10.1093 / mnras / stab837

Provided by the Harvard-Smithsonian Center for Astrophysics

Citation: Building planets from protoplanetary disks (2021, October 29) retrieved October 30, 2021 from https://phys.org/news/2021-10-planets-protoplanetary-discs.html

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