A transmission spectrum of WASP-17b — a hot-Jupiter exopanet around 1,300 light-years away — captured by the Mid-Infrared Instrument (MIRI) on the NASA/ESA/CSA James Webb Space Telescope reveals the first evidence for quartz (crystalline silica, SiO2) in the clouds of an exoplanet.
WASP-17b is located approximately 1,300 light-years from Earth in the constellation of Scorpius.
First discovered in 2009, this planet orbits the F-type main sequence star WASP-17.
With a volume more than 7 times that of Jupiter and a mass less than one-half of Jupiter, WASP-17b 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.
“We were thrilled! We knew from Hubble observations that there must be aerosols — tiny particles making up clouds or haze — in WASP-17b’s atmosphere, but we didn’t expect them to be made of quartz,” said Dr. David Grant, an astronomer at the University of Bristol.
Using Webb’s MIRI instrument, Dr. Grant and colleagues 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, they were 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.
While these crystals are probably similar in shape to the pointy hexagonal prisms found in geodes and gem…
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