This artist’s concept shows what the exoplanet WASP-17 b could look like. WASP-17 b, also called Ditsö̀, is a hot gas giant that orbits its star at a distance of just 0.051 AU (about 4.75 million miles, or one-eighth the distance between Mercury and the Sun), completing one full circuit in about 3.7 Earth-days. The system lies within the Milky Way, about 1,300 light-years from Earth, in the constellation Scorpius. With a volume more than seven times that of Jupiter and a mass less than one-half of Jupiter, WASP-17 b is an extremely puffy planet. Its short orbital period, large size, and thick, extended atmosphere make it ideal for observation using transmission spectroscopy, which involves measuring the effects of the planet’s atmosphere on the starlight filtering through it. Credit: NASA, ESA, CSA, Ralf Crawford (STScI)
Flakes of silica “snow” fill the skies of puffy, searing-hot exoplanet WASP-17 b.
Catching a glimpse of one of the most common and familiar minerals on Earth rarely merits a headline. Quartz is found in beach sands, building stones, geodes, and gem shops around the world. It’s melted to produce glass, refined for silicon microchips, and used in watches to keep time.
So what’s so special about the latest discovery from
Webb’s unique ability to measure the extremely subtle effects of those crystals on starlight – and from a distance of more than seven million billion miles, no less – is providing critical information about the composition of exoplanet atmospheres and new insights into their weather.
A transmission spectrum of the hot gas giant exoplanet WASP-17 b captured by MIRI (Webb’s Mid-Infrared Instrument) on March 12-13, 2023, reveals the first evidence for quartz (crystalline silica, SiO2) in the clouds of an exoplanet.
The spectrum was made by measuring the change in brightness of 28 wavelength-bands of mid-infrared light as the planet transited its star. Webb observed the WASP-17 system using MIRI’s low-resolution spectrograph for nearly 10 hours, collecting more than 1,275 measurements before, during, and after the transit.
For each wavelength, the amount of light blocked by the planet’s atmosphere (white circles) was calculated by subtracting the amount that made it through the atmosphere from the amount originally emitted by the star.
The solid purple line is a best-fit model to the Webb (MIRI), Hubble, and Spitzer data. (The Hubble and Spitzer data cover wavelengths from 0.34 to 4.5 microns and are not shown on the graph.) The spectrum shows a clear feature around 8.6 microns, which astronomers think is caused by silica particles absorbing some of the starlight passing through the atmosphere.
The dashed yellow line shows what that part of the transmission spectrum would look like if the clouds in WASP-17 b’s atmosphere did not contain SiO2.
This marks the first time that SiO2 has been identified in an exoplanet, and the first time any specific cloud species has been identified in a transiting exoplanet.
Credit: NASA, ESA, CSA, Ralf Crawford (STScI), David Grant (University of Bristol), Hannah R. Wakeford (University of Bristol), Nikole Lewis (Cornell University)
Webb Space Telescope Detects Tiny Quartz Crystals in Clouds of Hot Gas Giant
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
“We were thrilled!” said David Grant, a researcher at the
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.”
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.
Crystals, Clouds, and Winds
While these crystals are probably similar in shape to the pointy hexagonal prisms found in geodes and gem shops on Earth, each one is only about 10 nanometers across – one-millionth of one centimeter.
“Hubble data actually played a key role in constraining the size of these particles,” explained co-author Nikole Lewis of Cornell University, who leads the Webb Guaranteed Time Observation (GTO) program designed to help build a three-dimensional view of a hot Jupiter atmosphere. “We know there is silica from Webb’s MIRI data alone, but we needed the visible and near-infrared observations from Hubble for context, to figure out how large the crystals are.”
Unlike mineral particles found in clouds on Earth, the quartz crystals detected in the clouds of WASP-17 b are not swept up from a rocky surface. Instead, they originate in the atmosphere itself. “WASP-17 b is extremely hot – around 2,700 degrees
Reference: “JWST-TST DREAMS: Quartz Clouds in the Atmosphere of WASP-17b” by David Grant, Nikole K. Lewis, Hannah R. Wakeford, Natasha E. Batalha, Ana Glidden, Jayesh Goyal, Elijah Mullens, Ryan J. MacDonald, Erin M. May, Sara Seager, Kevin B. Stevenson, Jeff A. Valenti, Channon Visscher, Lili Alderson, Natalie H. Allen, Caleb I. Cañas, Knicole Colón, Mark Clampin, Néstor Espinoza, Amélie Gressier, Jingcheng Huang, Zifan Lin, Douglas Long, Dana R. Louie, Maria Peña-Guerrero, Sukrit Ranjan, Kristin S. Sotzen, Daniel Valentine, Jay Anderson, William O. Balmer, Andrea Bellini, Kielan K. W. Hoch, Jens Kammerer, Mattia Libralato, C. Matt Mountain, Marshall D. Perrin, Laurent Pueyo, Emily Rickman, Isabel Rebollido, Sangmo Tony Sohn, Roeland P. van der Marel and Laura L. Watkins, 16 October 2023, The Astrophysical Journal Letters.
DOI: 10.3847/2041-8213/acfc3b
The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (