It Rains Sand on the “Fluffy” Exoplanet Wasp-107B

wasp-107b

A team of European astronomers utilized the James Webb Space Telescope (JWST) to scrutinize the gas envelope of a nearby exoplanet in greater detail. Through an in-depth examination using specialized instruments in the atmosphere of WASP-107b, the researchers not only identified water vapor and sulfur dioxide but also observed silicate sand clouds.

With these advanced scientific capabilities, astronomers can unravel the mysteries of exoplanets. Instruments on the James Webb Telescope, the largest space-based mirror telescope, facilitate particularly promising investigations into celestial bodies. One such instrument is the Mid-Infrared Instrument (MIRI), integrated with the JWST.

Smaller and Lighter Than the Sun

This instrument functions as a virtual laboratory in space, detecting heat radiation from gas and microscopic dust. The data obtained allows scientists to infer the presence of molecules in space and examine the composition of fine dust in the universe.

Michiel Min and his team from the SRON Netherlands Institute for Space Research used MIRI to study the exoplanet WASP-107b, which orbits around WASP-107, a slightly cooler and less massive star, about 200 light-years away in the “Virgo” constellation. The planet, discovered in 2017, has similarities to Neptune in mass but is closer in size to Jupiter.

Previous observations in 2018, conducted with the Hubble Space Telescope, had detected helium in the atmosphere of WASP-107b. However, the more advanced capabilities of MIRI enabled a more detailed analysis of the composition of clouds on the exoplanet. The results of this analysis have been published in the scientific journal Nature.

The distinctive characteristics of the planet’s atmosphere, which the astronomers described as particularly “fluffy,” made this observational success possible. The collaborative study, involving the development of MIRI since 2003, contributes significantly to our understanding of the atmospheric composition of distant exoplanets.

The "fluffy" world allowed the scientists to look particularly deep into the atmosphere with the James Webb telescope.
The “fluffy” world allowed the scientists to look particularly deep into the atmosphere with the James Webb telescope. Image: LUCA School of Arts, Belgium/ Klaas Verpoest (visuals), Johan Van Looveren.

Surprising Sulphur Dioxide

The transmission spectrum of the exoplanet WASP-107b comes from the low-resolution spectrometer
The transmission spectrum of the exoplanet WASP-107b comes from the low-resolution spectrometer (LRS) of the Mid-Infrared Instrument (MIRI) on board the JWST. It shows evidence of water vapor, sulfur dioxide and sand clouds in the planet’s atmosphere. Image: Michiel Min / European MIRI EXO GTO team / ESA / NASA.

This combination results in a relaxed outer shell of the exoplanet, allowing researchers to peer about 50 times deeper into the atmosphere with MIRI than would be possible with Jupiter. This enables the identification of water vapor, sulfur dioxide (SO2), and silicate clouds, while methane (CH4) remains elusive.

The absence of methane suggests a potentially warm interior, providing valuable insights into the movement of thermal energy within the planet’s atmosphere. Furthermore, the discovery of sulfur dioxide, known for the smell of burnt matches, was surprising as previous models had predicted its absence, according to the Vienna-based astrophysicist.

Researchers attribute the unexpected finding to the fact that the host star of the celestial body sends relatively little light and, consequently, less energy to WASP-107b. However, this energy can penetrate deeper into the interior, favoring the formation of sulfur dioxide.

Sand Clouds

The exoplanet WASP-107b, which is around 200 light years away, orbits its parent star in a comparatively close orbit.
The exoplanet WASP-107b, which is around 200 light years away, orbits its parent star in a comparatively close orbit. Image: ESA/Hubble, NASA.

The data, however, also indicate that high-altitude clouds in the atmosphere partially obscure water vapor and sulfur dioxide. These clouds, however, have a composition entirely different from what is known on Earth: they consist of tiny silicate particles, the main component of sand. The discovery of clouds of sand, water, and sulfur dioxide on this fluffy exoplanet by JWST’s MIRI instrument is a pivotal milestone. It reshapes our understanding of planetary formation and evolution, shedding new light on our own Solar System, as Prof. Leen Decin points out.

In addition to the sand clouds, there are indications of actual sand rain on this distant celestial body. The clouds cause sand particles to rain down at temperatures of around 500 degrees Celsius. The observation of these sand clouds high in the atmosphere implies that the sand raindrops must evaporate in deeper, very hot layers, and the resulting silicate vapor is efficiently transported back up, where it condenses again into silicate clouds.

This continuous cycle of sublimation and condensation through vertical transport is similar to the water vapor and cloud cycle on Earth, albeit with sand droplets, explained lead author Michiel Min. This process is responsible for the persistent presence of sand clouds in the atmosphere of WASP-107b, according to the astrophysicist.

Source: https://dx.doi.org/10.1038/s41586-023-06849-0