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The Hubble Space Telescope has photographed a newly discovered exoplanet, called AB Aurigae b, in the act of formation. Observing the formative moment of a faraway world is already exciting enough – but researchers believe that this world came to be in a truly peculiar way.
As reported in Nature Astronomy, the planet appears to be forming due to “disk instability.” In this scenario – which has been long-debated – a large clump of gas in the disk surrounding the star collapses on itself, forming a gas giant planet.
This goes against the dominant theory of Jupiter-like planet formation called core-accretion, where planets deep in the disk slowly accumulate material, growing and growing over time. This latter method takes a fair bit of time – time that AB Aurigae b doesn’t have.
The star system is 2 million years old, and the planet is over two times further than Pluto is from the Sun. At that distance, a planet now nine times more massive than Jupiter could have only formed through disk instability.
"Nature is clever; it can produce planets in a range of different ways," lead researcher Thayne Currie of the Subaru Telescope and Eureka Scientific, said in a statement.
The discovery was only possible thanks to the many observations of the system through the years. The power and longevity of Hubble, now in its thirty-second year of operation, together with the Subaru Telescope in Hawaii provided the necessary details to understand what the system is like.
"We could not detect this motion on the order of a year or two years," Currie said. "Hubble provided a time baseline, combined with Subaru data, of 13 years, which was sufficient to be able to detect orbital motion."
There is still so much that we do not understand about the formation of exoplanets, despite now having confirmed over 5,000 such worlds. The more observations of the early years of star systems, the more our picture will become complete.
"This new discovery is strong evidence that some gas giant planets can form by the disk instability mechanism," Alan Boss of the Carnegie Institution of Science in Washington, D.C. emphasized. "In the end, gravity is all that counts, as the leftovers of the star-formation process will end up being pulled together by gravity to form planets, one way or the other."
NASA’s new space telescope, the JWST, has the right capabilities to take this work further and event better understand what goes on around AB Aurigae and in many other baby star systems.
