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This is a\u00a0transmission spectrum<\/a>\u00a0of the hot gas giant exoplanet WASP-17 b captured by the NASA\/ESA\/CSA James Webb Space Telescope’s<\/a> innovative Mid-Infrared Instrument (MIRI<\/a>)\u00a0on 12\u201313 March 2023. It reveals the first evidence for quartz (crystalline silica, SiO2<\/sub>) in the clouds of an exoplanet.<\/p>\n This marks the first time that SiO2<\/sub> has been identified in an exoplanet, and the first time any specific cloud species has been identified in a transiting exoplanet.<\/p>\n The 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 1275 measurements before, during, and after the transit.<\/p>\n For 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.<\/p>\n The solid purple line is a best-fit model to the Webb (MIRI), Hubble<\/a>, and Spitzer<\/a> 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.<\/p>\n