Earth and most of the other planets in the solar system formed by accretion – the slow accumulation of dust and large chunks. Until now, however, it has been disputed whether this mechanism of planet formation also applies to gaseous planets such as Jupiter or Saturn which orbit further out. Because at this distance from the sun there was actually not enough dust available as building material, they could also have been formed by a local collapse of gas – similar to star formation. So far, however, there is no evidence of this.
Astronomers are also puzzled as to how certain exoplanets could have formed. Because these young gas giants sometimes orbit 50 to 200 astronomical units from their star and therefore in a rather thin and material-poor area of their protoplanetary disk. However, since previously imaged protoplanets such as PDS 70 b were already several million years old, astronomers cannot rule out the possibility that they formed further inland and then migrated inward. outside.
Young, heavy and far from the star
Astronomers led by Thayne Currie of the National Astronomical Observatory of Japan may have discovered clearer evidence of the formation in place of a gas giant in distant orbit. Using the Subaru Telescope in Hawaii and the Hubble Space Telescope, they took a closer look at young AB Aurigae stars, 520 light-years away. In this case, telescopes had previously found evidence of at least one planetary embryo.
The new records confirm this. They show a distinct bright point of light that is about 93 astronomical units from its star – it orbits about three times farther than Neptune in our solar system. The protoplanet, dubbed AB Aurigae b, weighs about nine times the mass of Jupiter and is almost three times the size of Jupiter. Based on the spectral characteristics of the bright spot, the team also concludes that it must be a protoplanet around a million years old. “It therefore represents an earlier stage in the formation of planets than the PDS-70 system,” explain the astronomers.
Features support gas collapse formation
Also interesting: the protoplanet is close to one of the spiral arms that crosses the disc of gas and dust around the young star. “AB Aurigae b appears as a distinct tuft surrounding these arms,” the team said. “Thus, the characteristics of this protoplanet are strikingly similar to models of planet formation by gas instabilities.” According to these models, local gas collapse in protoplanetary disks can drive such spiral turbulence.
This is corroborated by another observation of the astronomers: the telescopic images show two more distant luminous points, which could come from other planetary embryos. At a distance of 430 and 580 astronomical units, these young planets are even further from their star. They too were therefore probably not formed by classical accretion.
A new look at “our” gas giants?
“This evidence of at least one protoplanet at a great distance from AB Aurigae has important implications for our understanding of planet formation,” Currie and colleagues say. “AB Aurigae b may provide us with the first direct evidence that Jupiter-like planets can form from gaseous instabilities.”
If confirmed, it would also shed new light on the formation of gas giants in our own solar system. Also for Jupiter and Saturn, one wonders if they were created by local gas collapse instead of accretion.
Source: Natural Astronomy
Author: Nadja Podbregar
You might also be interested in: