Scientists have discovered an enormous planet nine times the mass of Jupiter at a remarkably early stage of formation – describing it as still in the womb – in a discovery that calls into question current theories about planetary formation.
To detect and study the planet, a gas giant orbiting unusually far from its young host star, the researchers used the Subaru Telescope, which is located near the summit of an inactive Hawaiian volcano, and the Hubble Space Telescope, which is orbiting in space.
Gas giants, like our solar system’s largest planets Jupiter and Saturn, are composed primarily of hydrogen and helium, with swirling gases encircling a smaller solid core.
“We think it is still very early on in its ‘birthing’ process,” said astrophysicist Thayne Currie of the Subaru Telescope and the NASA-Ames Research Center, lead author of the study published on Monday in the journal Nature Astronomy.
“Evidence suggests that this is the earliest stage of formation ever observed for a gas giant”.
9.5 trillion km from Earth
It is embedded in an expansive disk of gas and dust that surrounds a star called AB Aurigae, which is located 508 light-years away from Earth.
This star got a fleeting moment of fame when its image appeared in a scene in the 2021 film ‘Don’t Look Up’
About 5,000 planets beyond our solar system, or exoplanets, have been identified. This one, known as AB Aur b, is one of the largest. It is getting close to the maximum size for classification as a planet rather than a brown dwarf, a body halfway between a planet and a star. It’s heated by gas and dust that falls into it.
Only one other star has been observed to have planets in the process of formation, known as protoplanets.
Almost all known exoplanets orbit their stars within the distance between our sun and its most distant planet, Neptune. But this planet orbits three times as far as Neptune from the sun and 93 times Earth’s distance from the sun.
Its birth appears to be following a different process than the standard planetary formation model.
‘Discovery challenges our understanding’
“The conventional thinking is that most – if not all – planets form by the 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 study co-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 evolve from dust to boulder-sized solid objects, and if this core reaches several times the mass of Earth, it will begin to accumulate gas from the disk.
“This process cannot form giant planets at a large orbital distance, so this discovery challenges our understanding of planet formation,” Guyon said.
Instead, the researchers believe AB Aur b forms in a scenario in which the disk surrounding the star cools and gravity causes it to fragment into one or more massive clumps that form planets.
“There’s more than one way to cook an egg,” Currie said. “And apparently there may be more than one way to form a Jupiter-like planet”.
The star AB Aurigae is roughly 2.4 times the mass of our sun and nearly 60 times brighter. It is about 2 million years old – a baby by stellar standards – compared to our middle-aged sun, which is about 4.5 billion years old. Early in its life, the sun was also surrounded by a disk, which gave rise to Earth and the other planets.
“New astronomical observations continuously challenge our current theories, ultimately improving our understanding of the universe,” Guyon said. “Planet formation is very complex and messy, with many surprises still ahead”.
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