Exoplanets & Exomoons

Webb Detects Tiny Quartz Crystals in Clouds of Hot Gas Giant WASP-17 b

By Keith Cowing
Press Release
November 4, 2023
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Webb Detects Tiny Quartz Crystals in Clouds of Hot Gas Giant WASP-17 b
The atmosphere of the hot gas giant planet WASP-17 b, depicted in this artist’s concept

The atmosphere of the hot gas giant planet WASP-17 b, depicted in this artist’s concept, is composed primarily of hydrogen and helium, along with small amounts of water vapor and hints of carbon dioxide and other molecules. Credit: NASA, ESA, CSA, and R. Crawford (STScI)

The finding tells scientists about the variety of materials that shape planetary environments, based on data from the MIRI instrument, which JPL managed through launch.

Researchers using NASA’s James Webb Space Telescope have detected evidence for quartz nanocrystals in the high-altitude clouds of WASP-17 b, a hot Jupiter exoplanet 1,300 light-years from Earth. The detection, which was uniquely possible with Webb’s MIRI (Mid-Infrared Instrument), marks the first time that silica (SiO2) particles have been spotted in an exoplanet atmosphere.

“We were thrilled!” said David Grant, a researcher at the University of Bristol in the U.K. and first author on a paper being published today in the Astrophysical Journal Letters. “We knew from Hubble observations that there must be aerosols – tiny particles making up clouds or haze – in WASP-17 b’s atmosphere, but we didn’t expect them to be made of quartz.”

Silicates (minerals rich in silicon and oxygen) make up the bulk of Earth and the Moon as well as other rocky objects in our solar system, and are extremely common across the galaxy. But the silicate grains previously detected in the atmospheres of exoplanets and brown dwarfs appear to be made of magnesium-rich silicates like olivine and pyroxene, not quartz alone – which is pure SiO2.

The result from this team, which also includes researchers from NASA’s Ames Research Center and NASA’s Goddard Space Flight Center, puts a new spin on our understanding of how exoplanet clouds form and evolve. “We fully expected to see magnesium silicates,” said co-author Hannah Wakeford, also from the University of Bristol. “But what we’re seeing instead are likely the building blocks of those, the tiny ‘seed’ particles needed to form the larger silicate grains we detect in cooler exoplanets and brown dwarfs.”

Waves of light detected in the clouds of the hot gas giant exoplanet WASP-17 b revealed the presence of quartz (crystalline silica, SiO2), as shown in this graph. This marks the first time that SiO2 has been identified in an exoplanet. Credit: NASA, ESA, CSA, and R. Crawford (STScI). Science: Nikole Lewis (Cornell University), David Grant (University of Bristol), Hannah Wakeford (University of Bristol) from the Space Telescope Science Institute.

Detecting Subtle Variations

With a volume more than seven times that of Jupiter and a mass less than one-half of Jupiter, WASP-17 b is one of the largest and puffiest known exoplanets. This, along with its short orbital period of just 3.7 Earth days, makes the planet ideal for transmission spectroscopy: a technique that involves measuring the filtering and scattering effects of a planet’s atmosphere on starlight.

Webb observed the WASP-17 system for nearly 10 hours, collecting more than 1,275 brightness measurements of 5- to 12-micron mid-infrared light as the planet crossed its star. By subtracting the brightness of individual wavelengths of light that reached the telescope when the planet was in front of the star from those of the star on its own, the team was able to calculate the amount of each wavelength blocked by the planet’s atmosphere.

What emerged was an unexpected “bump” at 8.6 microns, a feature that would not be expected if the clouds were made of magnesium silicates or other possible high-temperature aerosols like aluminum oxide, but which makes perfect sense if they are made of quartz.

JWST-TST DREAMS: Quartz Clouds in the Atmosphere of WASP-17b, Astrophysical Letters (open access)


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