This is the first time that quartz has been identified in the atmosphere of an exoplanet, and it was the James Webb Telescope that made this discovery possible, which is also the first of a specific type of cloud to be identified during transits on an exoplanet.
The Festival of Discoveries with the James Webb Space Telescope (JWST) does not disappoint, although unfortunately Hubert Reeves is no longer here to comment on it. This time and as explained in a NASA press release, Hubble’s successor has set its sights on WASP-17 b, one of the three exoplanets targeted by the Dreams (Deep Reconnaissance of Exoplanet Atmospheres) research program, a comprehensive collection of observations of a representative of each key class of exoplanets : a hot Jupiter, a hot Neptune and a temperate rocky planet.
WASP-17 b is a hot Jupiter located about 1,300 light-years from Earth and located in the mid-infrared using the Miri instrument (Webb’s mid-infrared instrument), discovered by David Grant, a researcher at the University of Bristol in the United Kingdom has. made the discovery with his colleagues. Discovery was published in an article in Astrophysical Journal Letters and can be read for free on arXiv.
“We were thrilled! “We knew from Hubble observations that there must be aerosols – tiny particles that form clouds or haze – in the atmosphere of WASP-17 b, but we did not expect them to be made of quartz,” explains the astrophysicist in the NASA press release.
“We fully expected to see magnesium silicates. But what we see instead are likely the building blocks of these particles, the tiny “seed” particles needed to form the larger silicate grains we discover in cooler exoplanets and brown dwarfs,” he explains. his colleague and co-author of the article, Hannah Wakeford, also from the University of Bristol.
Clouds of polymerized silicates
Astrophysicists have clearly identified the spectral signature of quartz nanocrystals in the high-altitude clouds of WASP-17 b. Remember that quartz, even though it has the chemical formula SiO2, is part of tectosilicates, which are minerals formed by connecting tetrahedral elementary patterns [SiO4]4− through all its vertices. So they are a kind of large polymerized molecules that form a crystal lattice.
It is not the first time that silicates, minerals rich in silicon and oxygen, have been detected in the atmosphere of exoplanets. These also included magnesium-rich minerals such as olivine and pyroxene. We can even cite the case of olivine crystals observed in exocomets with the defunct Spitzer telescope. We can even say that observations made over the years show that silicates are very common in the Milky Way and therefore rocky planets like Earth, which also contain a lot of silicates, may not be uncommon in the observable cosmos.
However, this is the first time that we have found the spectral signature of quartz crystals, a silicate largely described by the formula SiO2. This is not the case with olivine crystals such as forsterite with the formula Mg2SiO4 or even fayalite with the formula Fe2SiO4. It is even worse for pyroxenes, of which the example of augite is sufficient to show it as (Ca,Na)(Mg,Fe,Al).[(Si,Al)O3]2.
Quartz clouds discovered during planetary transits
Analysis of hot Jupiter’s atmosphere was facilitated by the fact that the exoplanet has a volume more than seven times that of Jupiter, although its mass is less than half that. This is due to the fact that WASP-17 b is one of the largest and most inflated exoplanets known due to its proximity to its star, giving it a temperature capable of melting certain metals. The greatly expanded atmosphere therefore makes it the ideal planet for transmission spectroscopy: a technique that consists of measuring the filtering and scattering effects of a planet’s atmosphere on starlight, in this case the Sun. from WASP-17 b. Webb observed the WASP-17 system for nearly ten hours and collected more than 1,275 measurements of light brightness in the mid-infrared range from 5 to 12 micrometers.
Methods for discovering exoplanets have changed significantly since the 1990s and can be divided into two main categories: direct methods and indirect methods. The three main methods are the direct imaging method, the indirect transit method and the indirect radial velocity method. Discover exoplanets in our nine-part web series. Every week there is a video on our YouTube channel. A playlist proposed by the CEA and the University of Paris-Saclay as part of the European research project H2020 Exoplanets-A. © CEA Research
David Grant also explains that when it comes to quartz nanocrystals, “WASP-17 b is extremely hot – about 1,500 degrees Celsius – and the pressure at which they form in the atmosphere is only about a thousandth of what we are at the earth’s surface”, These solid crystals can form directly from the gas without first passing through a liquid phase.
The researcher adds that the clouds containing these crystals, the exact amount of which is difficult to determine, are “likely present along the day-night transition (the terminator), the area that our observations study” winds could move these tiny mineral particles at thousands of miles per hour.”
We can also assume that the nanocrystal clouds circulate around the planet but evaporate when they reach the warmer side of the day.