Astrophysics: “alternative” planet formation – MIR

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How do giant planets form?

Status: 18:27 | Reading time: 3 minutes

Saturn is one of the four giant planets in our solar system. Saturn is one of the four giant planets in our solar system.

Saturn is one of the four giant planets in our solar system.

Credit: Getty Images/Science Photo Library – MARK CHESNOK

Some giant planets are so far from their star that their formation cannot be explained using the classical model. Researchers are now finding evidence for an alternative formation model.

Astronomers now have a clear idea of ​​how the large gas planets Jupiter and Saturn formed in our solar system: First, large bodies of rock called planetesimals collided and formed the core of the future planet.

It then attracted a large amount of gas from the environment with its gravity. However, to their surprise, sky explorers have found giant planets for many stars that are so far from their star that this model of core accretion does not work.

For the first time, an international team of researchers has been able to directly observe the formation of such a planet.

The planet appears to be formed by the direct collapse of dense, cold gas in the protoplanetary disk around its young star. The Japanese showed it subaru telescope in Hawaii and images provided by the space telescope.

The planet’s place of origin could be somewhere else

This is the first evidence that giant planets can arise due to such gravitational instability. scientists write in the journal Nature Astronomy..

“Previous studies of planet formation used data from already developed planets,” explained Thane Curry, who works at the Japan Observatory in Hawaii, and his colleagues. “But the later position of the planet does not have to correspond to the place of its formation.”

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Artistic depiction of planet b Centauri b orbiting a binary star system with at least six times the mass of the Sun.

Therefore, it is important to observe the development process yourself. “Only direct imaging of protoplanets still in gas and dust disks around young stars can give us a clue to the formation of large gaseous planets.”

So the researchers, led by Curry, aimed two telescopes at the young star AB Aurigae, 520 light-years away, which was already known to be surrounded by a protoplanetary disk. Success: High-resolution images provided by the instruments show several helical structures and several seals in the gaseous disk.

A giant planet nine times the mass of Jupiter.

Thus, the most visible spot is a giant planet with a mass of about nine times that of Jupiter, but ten times the distance from its star.

Telescopic images of AB Aurigae show two more clusters further down the disk, at distances 90 and 120 times greater than the distance between Jupiter and the Sun.

“This means that for the first time we have direct evidence that such giant planets do indeed form at a great distance from their star,” Curry and his colleagues emphasize, “and this sharply contradicts the predictions of the core accretion model.” Because there simply aren’t enough planetesimals this far from a young star to form a planetary core.

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Dimethyl ether is in the background the Elephant Trunk Nebula, a dust cloud 2,400 light-years away.

So how do such giant planets form at such a great distance from their star? Fortunately, the team’s observations immediately provide an answer to this question: the spirals observed in the disk are exactly what the researchers expect from the process of gravitational instability.

In this case, random seals are formed in the disk, which collapse into a planet under the influence of its own gravity. In computer simulations of this process, the resulting helical structures are exactly the same as the Curry group has now demonstrated. The team’s observations provide, for the first time, direct evidence for this alternative planetary formation scenario.

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