The atmosphere of the exoplanet WASP-107b contains so much helium that it extends tens of kilometers into space.
WASP-107b's planetary core is much smaller than scientists previously thought for a gas giant of its size. With its extremely low density, WASP-107b is often called a "cotton candy" or "ultra-fluffy" planet. The new research was published in The Astronomical Journal on January 18.
WASP-107b is located 212 light-years from Earth. It orbits its host star at only 1/16 the distance between Earth and the Sun. Extreme heat from its proximity to its star causes the planet to puff up. Astronomers believe that WASP-107b is about the same size as Jupiter, the largest planet in our solar system, but only one-tenth as massive.
Atmosphere Analysis
WASP-107b has a very low density, with a core about four times the mass of Earth and an atmosphere that is 26 times Earth's mass. This means that the gaseous envelope comprises over 85% of the planet's mass.
An international team of astronomers led by Dr. Jessica Spake of the University of Exeter, UK, announced yesterday that they had detected helium in WASP-107b's atmosphere after more than a decade of searching. It is the first time that scientists have discovered helium on a planet outside our solar system.
The team used NASA's Hubble Space Telescope to observe WASP-107b. They detected helium by analyzing the infrared spectrum of the planet's atmosphere.
According to Dr. Spake, the study's lead author, this was a very difficult observation to make with current technology. New techniques allowed the scientists to detect the strong signature of helium in WASP-107b's atmosphere.
Exoplanet Characteristics
WASP-107b is one of the least dense gas planets known. It is about the size of Jupiter but only 12% as massive. WASP-107b is located about 200 light-years from Earth and takes over 6 days to orbit its host star.
The amount of helium detected in WASP-107b's atmosphere is so large that the planet's atmosphere extends tens of kilometers into space. This is also the first time such an extended atmosphere has been detected at infrared wavelengths. Because of its extended atmosphere, the planet is losing a significant amount of mass into space. It is estimated that WASP-107b has lost between 0.1% and 4% of its total atmospheric mass over the past billion years.
Origin and Evolution
"We have many questions regarding WASP-107b," said Caroline Piaulet, the study's first author and a researcher at the University of Montreal. "How did such a low-density planet form? How does it manage to hold onto its puffy atmosphere, especially so close to its host star? These questions motivate us to push further our analysis and try to uncover its formation history."
Scientists believe that gas giants like Jupiter and Saturn form when a large, rocky core, roughly 10 times the mass of Earth, accumulates gas from a disk of material surrounding a newborn star. Such a massive core was previously thought to be a necessary condition. However, WASP-107b suggests that this may not be accurate.
Combining observations from the James Webb Space Telescope's Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) with Hubble's Wide Field Camera 3 (WFC3), the two most powerful space telescopes currently in operation, the researchers measured the abundance of numerous molecules in WASP-107b's atmosphere.
These molecules include water vapor, methane, carbon dioxide, carbon monoxide, sulfur dioxide, and ammonia.
Hot Core and Atmospheric Circulation
Both the Hubble and James Webb spectra show a surprising lack of methane in WASP-107b's atmosphere: one thousand times less than expected based on its temperature of 500 degrees Celsius.
There is only one possible explanation: Despite its relatively "cool" surface temperature compared to other so-called "hot Jupiters," the cotton candy planet must have a very hot interior because methane is destroyed at high temperatures.
This internal heating could be caused by tidal heating due to its eccentric orbit. The varying gravitational pull as the planet swings closer to and farther from its parent star can stretch and flex the planet, causing it to heat up.
Once it was determined that the planet had enough internal heat to thoroughly stir its atmosphere, the researchers realized that the spectra could also provide a novel way to estimate the size of its core.
The results show that the planet's core is twice as large as previously thought. This larger, hotter core is the reason the planet has such a thick atmosphere and can maintain its cotton candy-like state over time.
In other words, it is a much hotter version of Neptune than Jupiter.