Scientists find world they thought couldn’t exist – and it could change our understanding of how planets form

(ESA/Hubble, NASA, M. Kornmesser)

A planet that scientists thought couldn’t exist could change our understanding of how new worlds form.

The planet, officially known as WASP-107b and referred to as a “super-puff”, is far less dense than was previously thought possible, scientists say.

It is roughly the same size as Jupiter – but is 10 times less dense, which has led researchers liken it to candy floss.

As such, the planet is notably not just on its own but for the “big implications” it has about the way gas-giant planets are able to form, suggesting they can come about much more easily than previously believed.

"This work addresses the very foundations of how giant planets can form and grow," said Björn Benneke from the University of Montreal. "It provides concrete proof that massive accretion of a gas envelope can be triggered for cores that are much less massive than previously thought."

The planet is remarkable not just for its unusual size but also its low surface gravity and the brightness of its star, which is known as WASP-107. That allows the world and its atmosphere to be studied in more detail than usual.

The researchers publish the new and breakthrough results of a four-year study of the system in the latest edition of the Astronomical Journal.

 WASP-107b was first found in 2017, orbiting around its star some 212 light-years away from Earth. It is very close to that star, about 16 times nearer than we are to our own Sun.

Further research has shown that it is one of the least dense planets ever to be found. It’s that very thin nature that led researchers to refer to it as a “super-puff” or a “cotton-candy” planet.

Planets are formed in the disc of dust and gas that swirls around young stars. It’s usually thought that gas giant planets like our own Jupiter and Saturn or WASP-107b need to create a solid core that is at least 10 times more massive than Earth, so that enough gas is accrued before the disc dissipates.

But WASP-107b does not have that massive a core, and so scientists are unsure how would be able to form in the first place. They do have a host of possible scenarios that might explain the unusual planet, however.

"For WASP-107b, the most plausible scenario is that the planet formed far away from the star, where the gas in the disc is cold enough that gas accretion can occur very quickly," said McGill University professor Eve Lee. "The planet was later able to migrate to its current position, either through interactions with the disc or with other planets in the system."

During the same research, scientists came across another planet in the system, known as WASP-107c. That is less remarkable – it has considerably more mass, and is much further from its star – but it has a strange orbit around the star and could be another clue to what happened to its sibling.

"WASP-107c has in some respects kept the memory of what happened in its system," said Piaulet. "Its great eccentricity hints at a rather chaotic past, with interactions between the planets which could have led to significant displacements, like the one suspected for WASP-107b."