In a discovery that challenges existing understanding of planetary formation, scientists have discovered a massive planet around nine times the mass of Jupiter at a relatively early stage of formation – describing it as still in the womb.
The planet, a gas giant orbiting exceptionally far from its young host star, was discovered and studied using the Subaru Telescope, which is perched atop the peak of an extinct Hawaiian volcano, and the Hubble Space Telescope, which is orbiting in space.
Planets comprised primarily of hydrogen and helium, such as Jupiter and Saturn in our solar system, have whirling gases encircling a tiny solid core.
“We think it is still very early on in its ‘birthing’ process,” said Subaru Telescope and NASA-Ames Research Center astrophysicist Thayne Currie, lead author of the study published in the journal Nature Astronomy on Monday.
“Evidence suggests that this is the earliest stage of formation ever observed for a gas giant”.
9.5 trillion kilometres from the Earth
It’s embedded in an expansive disc of gas and dust that surrounds a star named AB Aurigae, which is 508 light years away from Earth and contains the material that produces planets.
When this star’s image featured in a scene in the 2021 film ‘Don’t Look Up,’ it received a brief burst of renown.
Exoplanets, or planets outside our solar system, number around 5,000. This one, AB Aur b, is one of the biggest. It’s getting close to being large enough to be recognised as a planet rather than a brown dwarf, a body halfway between a planet and a star. Gas and dust dropping into it heat it up.
Only one other star has been discovered with planets in the process of development, known as protoplanets.
Almost all known exoplanets have orbits around their stars that are less than the distance between our solar and its furthest planet, Neptune. However, this planet orbits the sun three times as far as Neptune and 93 times as distant as Earth.
It appears to have formed in a way that differs from the usual planetary formation paradigm.
‘Discovery challenges our understanding’
“The conventional thinking is that most – if not all – planets form 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 study co-author Olivier Guyon of the Subaru Telescope and the University of Arizona.
In this scenario, protoplanets trapped in the disc encircling a young star progressively evolve from dust to boulder-sized solid objects, and then begin gathering gas from the disc if the core reaches several times Earth’s mass.
“This process cannot form giant planets at a large orbital distance, so this discovery challenges our understanding of planet formation,” Guyon added.
Instead, the researchers believe AB Aur b is forming in a scenario in which the star’s disc cools and fragments into one or more large clumps that produce planets due to gravity.
“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 over 60 times brighter and 2.4 times more massive than our sun. It’s just roughly 2 million years old, a child by stellar standards, compared to our 4.5 billion-year-old sun. Early in its life, the sun was also encircled by a disc, which gave birth 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.”