Webb Spots Quartz Crystals In Clouds Of Exoplanet WASP-17b

This is a transmission spectrum of the hot gas giant exoplanet WASP-17 b captured by the NASA/ESA/CSA James Webb Space Telescope’s innovative Mid-Infrared Instrument (MIRI) on 12–13 March 2023. It reveals the first evidence for quartz (crystalline silica, SiO2) in the clouds of an exoplanet.

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.

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’s low-resolution spectrograph for nearly 10 hours, collecting more than 1275 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.

JWST-TST DREAMS: Quartz Clouds in the Atmosphere of WASP-17b

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, Laura L. Watkins

Clouds are prevalent in many of the exoplanet atmospheres that have been observed to date. For transiting exoplanets, we know if clouds are present because they mute spectral features and cause wavelength-dependent scattering. While the exact composition of these clouds is largely unknown, this information is vital to understanding the chemistry and energy budget of planetary atmospheres. In this work, we observe one transit of the hot Jupiter WASP-17b with JWST’s MIRI LRS and generate a transmission spectrum from 5-12 μm. These wavelengths allow us to probe absorption due to the vibrational modes of various predicted cloud species. Our transmission spectrum shows additional opacity centered at 8.6 μm, and detailed atmospheric modeling and retrievals identify this feature as SiO2(s) (quartz) clouds. The SiO2(s) clouds model is preferred at 3.5-4.2σ versus a cloud-free model and at 2.6σ versus a generic aerosol prescription. We find the SiO2(s) clouds are comprised of small ∼0.01 μm particles, which extend to high altitudes in the atmosphere. The atmosphere also shows a depletion of H2O, a finding consistent with the formation of high-temperature aerosols from oxygen-rich species. This work is part of a series of studies by our JWST Telescope Scientist Team (JWST-TST), in which we will use Guaranteed Time Observations to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS).

Comments: 19 pages, 7 figures, accepted for publication in ApJL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2310.08637 [astro-ph.EP] (or arXiv:2310.08637v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2310.08637
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Submission history
From: David Grant
[v1] Thu, 12 Oct 2023 18:00:20 UTC (2,171 KB)
https://arxiv.org/abs/2310.08637