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.
Credits
Illustration
NASA, ESA, CSA, Ralf Crawford (STScI)
Science
David Grant (University of Bristol), Hannah R. Wakeford (University of Bristol), Nikole Lewis (Cornell University)
| About The Object | |
|---|---|
| Object Name | WASP-17 b (also called Ditsö̀) |
| Object Description | Hot Jupiter Exoplanet |
| R.A. Position | 15h59m50.94s |
| Dec. Position | -28d03m42.46s |
| Constellation | Scorpius |
| Distance | 1,300 light-years (400 parsecs) |
| Dimensions | Diameter: 1.9 × Jupiter; Mass: 0.48 × Jupiter |
| About The Data | |
| Data Description | Low-resolution time-series spectroscopy (5-12 microns) |
| Instrument | MIRI |
| Exposure Dates | March 12-13, 2023 |
| About The Object | |
|---|---|
| Object Name | A name or catalog number that astronomers use to identify an astronomical object. |
| Object Description | The type of astronomical object. |
| R.A. Position | Right ascension – analogous to longitude – is one component of an object's position. |
| Dec. Position | Declination – analogous to latitude – is one component of an object's position. |
| Constellation | One of 88 recognized regions of the celestial sphere in which the object appears. |
| Distance | The physical distance from Earth to the astronomical object. Distances within our solar system are usually measured in Astronomical Units (AU). Distances between stars are usually measured in light-years. Interstellar distances can also be measured in parsecs. |
| Dimensions | The physical size of the object or the apparent angle it subtends on the sky. |
| About The Data | |
| Data Description |
|
| Instrument | The science instrument used to produce the data. |
| Exposure Dates | The date(s) that the telescope made its observations and the total exposure time. |
| Filters | The camera filters that were used in the science observations. |
| About The Image | |
| Image Credit | The primary individuals and institutions responsible for the content. |
| Publication Date | The date and time the release content became public. |
| Color Info | A brief description of the methods used to convert telescope data into the color image being presented. |
| Orientation | The rotation of the image on the sky with respect to the north pole of the celestial sphere. |
