![\"Illustration](\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2023\/10\/stsci-01hc3ay82pxh352b641zrynnns.png?w=2048\")
<\/figure>\u201cWe were thrilled!\u201d said David Grant, a researcher at the University of Bristol in the UK and first author on a paper being published today in the Astrophysical Journal Letters<\/a>. \u201cWe knew from Hubble observations that there must be aerosols\u2014tiny particles making up clouds or haze\u2014in WASP-17 b\u2019s atmosphere, but we didn\u2019t expect them to be made of quartz.\u201d<\/p>\n<\/p>\n 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 \u2013 which is pure SiO2.<\/p>\n The result from this team, which also includes researchers from NASA\u2019s Ames Research Center and NASA\u2019s Goddard Space Flight Center, puts a new spin on our understanding of how exoplanet clouds form and evolve. \u201cWe fully expected to see magnesium silicates,\u201d said co-author Hannah Wakeford, also from the University of Bristol. \u201cBut what we\u2019re seeing instead are likely the building blocks of those, the tiny \u2018seed\u2019 particles needed to form the larger silicate grains we detect in cooler exoplanets and brown dwarfs.\u201d<\/p>\n<\/p>\n With a volume more than seven times that of Jupiter and a mass less than one-half 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> : a technique that involves measuring the filtering and scattering effects of a planet\u2019s atmosphere on starlight.<\/p>\n 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\u2019s atmosphere.<\/p>\n What emerged was an unexpected \u201cbump\u201d at 8.6 microns<\/a>, 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.<\/p>\n<\/p>\n Download full resolution images for this article from the Space Telescope Science Institute (STScI)<\/a><\/strong><\/p>\n<\/p>\n 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\u2014one-millionth of one centimeter.<\/p>\n \u201cHubble data actually played a key role in constraining the size of these particles,\u201d explained co-author Nikole Lewis of Cornell University, who leads the Webb Guaranteed Time Observation (GTO) program<\/a> designed to help build a three-dimensional view of a hot Jupiter atmosphere. \u201cWe know there is silica from Webb\u2019s MIRI data alone, but we needed the visible and near-infrared observations from Hubble for context, to figure out how large the crystals are.\u201d<\/p>\n 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. \u201cWASP-17 b is extremely hot\u2014around 1,500 degrees Celsius (2,700\u00b0F)\u2014and the pressure where they form high in the atmosphere is only about one-thousandth of what we experience on Earth\u2019s surface,\u201d explained Grant. \u201cIn these conditions, solid crystals can form directly from gas, without going through a liquid phase first.\u201d<\/p>\n Understanding what the clouds are made of is crucial for understanding the planet as a whole. Hot Jupiters like WASP-17 b are made primarily of hydrogen and helium, with small amounts of other gases like water vapor (H2O) and carbon dioxide (CO2). \u201cIf we only consider the oxygen that is in these gases, and neglect to include all of the oxygen locked up in minerals like quartz (SiO2), we will significantly underestimate the total abundance,\u201d explained Wakeford. \u201cThese beautiful silica crystals tell us about the inventory of different materials and how they all come together to shape the environment of this planet.\u201d<\/p>\n Exactly how much quartz there is, and how pervasive the clouds are, is hard to determine. \u201cThe clouds are likely present along the day\/night transition (the terminator), which is the region that our observations probe,\u201d said Grant. Given that the planet is tidally locked with a very hot day side and cooler night side, it is likely that the clouds circulate around the planet, but vaporize when they reach the hotter day side. \u201cThe winds could be moving these tiny glassy particles around at thousands of miles per hour.\u201d<\/p>\n WASP-17 b is one of three planets targeted by the JWST-Telescope Scientist Team\u2019s<\/a> Deep Reconnaissance of Exoplanet Atmospheres using Multi-instrument Spectroscopy (DREAMS) investigations, which are designed to gather a comprehensive set of observations of one representative from each key class of exoplanets: a hot Jupiter, a warm Neptune, and a temperate rocky planet. The MIRI observations of hot Jupiter WASP-17 b were made as part of GTO program 1353<\/a>.<\/p>\n The James Webb Space Telescope is the world\u2019s 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 (European Space Agency) and the Canadian Space Agency.<\/p>\n<\/p>\n<\/p>\n Media Contacts:<\/strong><\/em><\/p>\n Laura\u00a0Betz<\/strong><\/em> Christine\u00a0Pulliam<\/strong><\/em>Detecting Subtle Variations<\/h2>\n
![alt=\"Graphic titled \u201cHot Gas Giant Exoplanet WASP-17 b Composition of Cloud Particles, MIRI Low-Resolution Time-Series Spectroscopy\u201d showing 28 data points plotted as white circles with vertical error bars on a graph of amount of light blocked in percent on the y-axis versus wavelength of light in microns on the x-axis. The y-axis ranges from 1.45 to 1.65 percent. The x-axis ranges from 5 to 12 microns. A jagged purple line is labeled \u201cModel spectrum based on Webb, Hubble, and Spitzer data.\u201d One broad, prominent peak visible in the data and model is highlighted with a vertical green band labeled \u201cLight blocked by quartz (S I O 2) crystals.\u201d The peak is centered at about 8.6 microns and 1.59 percent. Running across the green band below the purple peak, is a jagged dashed yellow line labeled \u201cWhat the spectrum would look like with no quartz clouds.\u201d This line slopes down to the right. In the background is an illustration of a planet with wispy clouds and a hazy blueish glow along the horizon.\"](\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2023\/10\/stsci-01hcjc3jfvr4jjq96jp0wgamg1.png?w=2048\")
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\nThe spectrum was made by measuring the change in brightness of 28 wavelength-bands of mid-infrared light as the planet transited the star. Webb observed the WASP-17 system using MIRI\u2019s low-resolution spectrograph for nearly 10 hours, collecting more than 1,275 measurements before, during, and after the transit.
\nFor each wavelength, the amount of light blocked by the planet\u2019s atmosphere (white circles) was calculated by subtracting the amount that made it through the atmosphere from the amount originally emitted by the star.
\nThe 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.
\nThe dashed yellow line shows what that part of the transmission spectrum would look like if the clouds in WASP-17 b\u2019s atmosphere did not contain SiO2.
\nThis 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.\n<\/div>\nCrystals, Clouds, and Winds<\/h2>\n
NASA\u2019s Goddard Space Flight Center, Greenbelt, Md.<\/strong><\/em>
laura.e.betz@nasa.gov<\/a><\/strong><\/em><\/p>\n
Space Telescope Science Institute, Baltimore, Md.<\/strong><\/em>
cpulliam@stsci.edu<\/a><\/strong><\/em><\/p>\nShare<\/h2>\n<\/div>\n