Astronomers have discovered a unique ‘super-puff’ planet that’s as big as Jupiter, but 10 times lighter.
The planet, called WASP-107b is believed to be one of the least dense exoplanets ever discovered, earning it the nicknames of a ‘super-puff’ or ‘cotton-candy’ planet.
Researchers say the findings have ‘big implications’ for what we understand about how giant planets form and grow.
WASP-107b is very close to its star, WASP-107, with estimates suggesting the planet is over 16 times to its star than the Earth is to the Sun
WASP-107b lies around 212 light years from Earth, in the Virgo constellation.
Estimates suggest the planet is over 16 times closer to its star, WASP-107, than the Earth is to the Sun.
Using observations obtained by the Keck Observatory in Hawaii, researchers from the University of Montreal have been able to determine the planet’s size and density.
Their results suggest that WASP-107b is around the same size as Jupiter, but is around 10 times lighter.
This extremely low density indicates that the planet must have a solid core of no more than four times the mass of Earth, according to the researchers.
This suggests that more than 85 per cent of its mass lies in the thick layer of gas that surrounds its core.
Caroline Piaulet, a PhD student at the University of Montreal, and lead author of the study, said: ‘We had a lot of questions about WASP-107b. How could a planet of such low density form?
‘And how did it keep its huge layer of gas from escaping, especially given the planet’s close proximity to its star?
‘This motivated us to do a thorough analysis to determine its formation history.’
Most gas giant planets, such as Jupiter and Saturn, have a solid core at least 10 times more massive than Earth.
Estimates suggest that the planet is around the same size as Jupiter, but is around 10 times lighter
However, WASP-107b has a much less massive core, leading the researchers to question how the planet was able to cross the critical threshold necessary to build up and retain its gas envelope.
Professor Eve Lee, a world-renowned expert on super-puff planets, has several theories.
‘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,’ she said.
‘The planet was later able to migrate to its current position, either through interactions with the disc or with other planets in the system.’
Surprisingly, previous data from Nasa’s Hubble spacecraft suggests WASP-107b contains very little methane.
Ms Piaulet said: ‘That’s strange, because for this type of planet, methane should be abundant. We’re now reanalysing Hubble’s observations with the new mass of the planet to see how it will affect the results, and to examine what mechanisms might explain the destruction of methane.’
WASP-107b is around the same size as Jupiter (pictured), but is 10 times lighter than the gas giant
The observations also revealed that WASP-107b isn’t alone in orbiting the star WASP-107 – it’s joined by another planet, called WASP-107c.
WASP-107c has a mass of about one-third of that of Jupiter, and is much further away from its central star than WASP-107b, taking three years to complete one orbit, as opposed to just 5.7 days.
Interestingly, the eccentricity of this second planet is high, meaning its trajectory is more oval than circular.
Ms Piaulet explained: ‘WASP-107c has in some respects kept the memory of what happened in its system.
‘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.’
The team hopes the findings will shed light on the different mechanisms of planet formation throughout the universe.
Ms Piaulet added: ‘Exoplanets like WASP-107b that have no analogue in our Solar System allow us to better understand the mechanisms of planet formation in general and the resulting variety of exoplanets. It motivates us to study them in great detail.’