James Webb discovers quartz crystals in the atmosphere of an exoplanet

Thanks to the James Webb Space Telescope (JWST), astronomers have discovered quartz crystals in the clouds of a hot gas giant. This is the first case of the detection of silica (SiO2) in the atmosphere of an extrasolar world.

“Bloated” world in retrograde orbit

The discovery was made during the study of the exoplanet WASP-17b, located at a distance of 310 light-years from Earth. This is a very unusual world. WASP-17b moves in a retrograde orbit around its star — that is, in the direction opposite to the rotation of the parent star. Its orbit passes at a distance of 7 million km from the sun, which is why the atmosphere of the exoplanet is heated to temperatures reaching 1500 °C. 

WASP-17 in the artist’s image. Source: Graphics: NASA, ESA, CSA, and R. Crawfor, d (STScI)Science: Nikole Lewis (Cornell University), David Grant (University of Bristol), Hannah Wakeford (University of Bristol) Crawford (STScI)

Another interesting feature of this world is its extreme “bloat“. With a radius that is almost twice the radius of Jupiter, the mass of the exoplanet is only 0.5 of Jupiter’s. This gives an average density of only 0.08 g/cm3, which is 12.5 times less than the density of water.

All this makes WASP-17b a very interesting target for spectroscopic studies that allow scientists to look into its atmosphere. The researchers used JWST for this purpose. It observed the system for 10 hours, having carried out more than 1,275 measurements in the mid-infrared range at wavelengths from 5 to 12 microns. By subtracting the brightness of individual wavelengths of light that reached the telescope when the planet was in front of the star from the brightness of the star itself, astronomers calculated the amount of light of each wavelength blocked by the planet’s atmosphere.

Quartz clouds

Prior to the observations, astronomers assumed that they would be able to find traces of aerosols consisting of magnesium silicates or aluminum oxide in the atmosphere of WASP-17b. But when they plotted the measurements, they found a “bump” at a wavelength of 8.6 microns that did not correspond to these compounds. The only model that explains the observation is the presence of clouds on the planet consisting of quartz crystals.

The obtained JWST spectrum of the WASP-17 atmosphere. Source:  NASA, ESA, CSA, and R. Crawfor, d (STScI)Science: Nikole Lewis (Cornell University), David Grant (University of Bristol), Hannah Wakeford (University of Bristol) Crawford (STScI)

Unlike the mineral particles found in clouds on Earth, quartz crystals found in WASP-17 b clouds do not rise from its surface. Instead, they arise in the atmosphere itself, directly from the gas. Subsequent observations made with the Hubble telescope helped determine their size. Although the shape of these crystals is probably similar to the pointy hexagonal prisms that can be found in geodes and gem shops on Earth, the size of each of them is only about 10 nanometers.

So far, researchers cannot estimate the exact number and extent of the prevalence of quartz clouds. Given that the gas giant is constantly turned towards the star by the same hemisphere, it is likely that clouds circulate around the planet but evaporate when they reach the hotter daytime side.

According to https://www.nasa.gov

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