The atmosphere of the exoplanet WASP-107b contains so much helium that it extends for tens of kilometers.
The core mass of the planet WASP-107b is much smaller than the standard for a gas giant core that scientists previously believed. With an extremely low density, WASP-107b is referred to as a “cotton candy” planet or a “super-puffed” planet. This new research was published in The Astronomical Journal on January 18.
WASP-107b is located 212 light-years away from Earth. This planet orbits its host star at a distance only 1/16 that of Earth to the Sun. It is heated due to its close proximity to the host star. Astronomers estimate that WASP-107b is roughly the size of Jupiter, the largest planet in the Solar System, but its mass is only 1/10 that of Jupiter.
WASP-107b has an extremely low density, with its core weighing about four times that of Earth, while its atmosphere weighs 26 times that of Earth. This means that the atmospheric layer constitutes over 85% of this planet’s total mass.
An international team of astronomers, led by Dr. Jessica Spake from the University of Exeter in the UK, announced yesterday the discovery of helium in the atmosphere of the exoplanet WASP-107b after more than a decade of searching. This marks the first time scientists have detected helium on a planet outside the Solar System.
Exoplanet WASP-107b.
The research team utilized the Hubble Space Telescope from NASA to observe the exoplanet WASP-107b. They discovered helium by analyzing the infrared spectrum of the planet’s atmosphere. According to Dr. Spake, the team leader, this was quite challenging with current technology. The new technique allowed the scientists to detect strong signals of helium in the atmosphere of exoplanet WASP-107b.
WASP-107b is one of the lowest-density gas planets known to date. It is approximately the size of Jupiter but has only 12% of its mass. WASP-107b is about 200 light-years away from Earth and takes over six days to orbit its host star.
The amount of helium detected in the atmosphere of WASP-107b is so substantial that its atmosphere extends for tens of kilometers into space. This is also the first time such an extended atmosphere has been detected at infrared wavelengths. Due to its expanding atmosphere, this planet loses a significant amount of gas to space as it moves. It is estimated that WASP-107b has lost about 0.1 – 4% of its total atmospheric mass over billions of years.
“We have many questions regarding WASP-107b. How does a planet with such low density form? How does it maintain its massive gaseous layer without losing it, especially while orbiting so close to its host star? These issues drive us to analyze further to understand its formation process,” Caroline Piaulet, the lead author of the study and an expert at the University of Montreal, shared.
Scientists believe that gas giants like Jupiter or Saturn form when a solid core of substantial mass, roughly 10 times that of Earth, accumulates a significant amount of gas from the disc of material surrounding a newly formed star. A large core mass was once considered a prerequisite. However, WASP-107b suggests that this may not be the case.
By combining observations from the Near Infrared Camera (NIRCam) and the Mid-Infrared Instrument (MIRI) of the James Webb Space Telescope with the Wide Field Camera 3 (WFC3) of Hubble, the two most powerful space telescopes currently, they measured the abundance of numerous molecules in the atmosphere of WASP-107b.
These molecules include water vapor, methane, carbon dioxide, carbon monoxide, sulfur dioxide, and ammonia.
Cotton Candy Planet WASP-107b – (Graphic: LUCA ART SCHOOL/NASA/ESA).
Both spectra from Hubble and James Webb show a surprising deficit of methane in the atmosphere of WASP-107b: only a fraction of the expected amount based on its temperature of 500 degrees Celsius.
There is only one possible explanation: despite having a “cool” surface temperature compared to other observed “hot Jupiters,” this cotton candy planet possesses a very hot core, as methane is unstable at high temperatures.
This internal heat could be due to tidal heating from its elliptical orbit. The gravitational pull changes as the planet moves closer and farther from its host star, stretching the planet and causing this phenomenon.
After determining that this planet has enough internal heat to fully stir its atmosphere, researchers realized that the spectrum could also provide a new method to estimate the size of the core.
The results indicated that the core of this planet is twice as large as originally expected. A larger and consistently hot core is the reason this planet has such a thick gaseous layer and maintains its cotton candy state over time.
In other words, it is more like a hot version of Neptune than Jupiter.
Now, new analysis continues to reveal the uniqueness of this planet: it has an asymmetric atmosphere.
In the graphic image provided by scientists – which would be a real image if we could magnify what is observed many times – WASP-107b resembles a floating egg with a solid core and asymmetrical translucent layers surrounding it as it drifts across its host star.
“This is the first time that East-West asymmetry of an exoplanet has been observed as it transits its host star, from space,” said astronomer Matthew Murphy from the University of Arizona (USA).
We have learned a bit about what is in the atmosphere of this peculiar exoplanet.
Previous analyses based on data from the James Webb Space Telescope showed that it features an atmosphere filled with sulfur dioxide, water vapor, carbon dioxide, carbon monoxide, and clouds of sand.
Dr. Murphy and colleagues want to go further. Using new analysis techniques, they found that there must be differences in the atmospheric composition between the eastern and western hemispheres of the planet, according to a paper published in the journal Nature Astronomy.
Scientists have previously identified atmospheric asymmetry in other exoplanets, though not through direct observation as this time.
In ultra-hot exoplanets, it is believed that the cause is the rotation of the atmosphere around the planet.
As it reaches the dawn boundary, it heats up; as it reaches the dusk boundary, it cools down, condenses, and may even rain.
But WASP-107b has brought a new breakthrough.
Not only is there a temperature difference on either side of the exoplanet, with cooler mornings than evenings, but there is also a slight difference in cloud opacity.
This is intriguing, as models suggest that WASP-107b should not exhibit such asymmetry.
While a difference in chemical composition is the most reasonable hypothesis, scientists have yet to pinpoint whether the atmosphere in the eastern hemisphere contains compounds that are absent in the western hemisphere, or vice versa.
They hope to answer that question with many more hours of observation.
