WASHINGTON, April 4 — Scientists have observed a giant planet about nine times the mass of Jupiter at a remarkably early stage of formation – they describe it as still in its mother’s womb – in a discovery that challenges current understanding of planet formation.
The researchers used the Subaru telescope, located near the top of an inactive Hawaiian volcano, and the orbiting Hubble Space Telescope to discover and study the planet, a gas giant orbiting an unusually far distance from its young host star. Gas giants are planets, like the largest in our solar system, Jupiter and Saturn, composed mostly of hydrogen and helium, with swirling gases surrounding a smaller solid core.
“We think it’s very early in its ‘birth’ process,” said astrophysicist Thayne Currie of the Subaru Telescope and NASA-Ames Research Center, lead author of the study published Monday in the journal natural astronomy. “Evidence suggests this is the earliest formation stage ever observed for a gas giant.”
It’s embedded in an expansive disc of gas and dust that supports the planet-forming material that surrounds a star called AB Aurigae, which is 508 light-years across — the distance light travels in a year, 5.9 trillion miles (9.5… trillion km) – away from Earth is . This star gained a fleeting moment of fame when his image appeared in a scene in the 2021 film Don’t Look Up.
About 5,000 planets outside our solar system, or exoplanets, have been identified. This one called AB Aur b is among the largest. It is approaching the maximum size to be classified as a planet rather than a brown dwarf, a body between a planet and a star. It is heated by falling gas and dust.
Planets in the process of formation – so-called protoplanets – have so far only been observed around one other star.
Almost all known exoplanets orbit their stars within the distance that separates our Sun from its most distant planet, Neptune. But this planet orbits three times as far from the Sun as Neptune and 93 times as far from the Sun as Earth.
Its birth appears to follow a different process than the standard model of planet formation.
“The conventional thinking is that most – if not all – planets are formed by slow accretion of solids onto a rocky core, and that gas giants go through this phase before the solid core is massive enough to start accreting gas,” said astronomer and fellow student author Olivier Guyon of the Subaru Telescope and the University of Arizona.
In this scenario, protoplanets embedded in the disk surrounding a young star gradually outgrow dust- to stone-sized solids and, when this core reaches several times Earth’s mass, begin accumulating gas from the disk.
“This process cannot form giant planets at great orbital distances, so this discovery challenges our understanding of planet formation,” Guyon said.
Instead, the researchers believe AB Aur b forms in a scenario where the disk around the star cools and gravity causes it to fragment into one or more massive clumps that form into planets.
“There’s more than one way to boil an egg,” Currie said. “And apparently there can be more than one way to form a Jupiter-like planet.”
The star AB Aurigae is about 2.4 times more massive than our Sun and nearly 60 times brighter. It is about 2 million years old – an infant by stellar standards – compared to about 4.5 billion years for our middle-aged Sun. The sun, too, was surrounded by a disc early in its life, from which the earth and the other planets emerged.
“New astronomical observations constantly challenge our current theories and ultimately improve our understanding of the Universe,” Guyon said. “Planet formation is very complex and chaotic, with many surprises yet to come.”
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