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Microscopic crystals suspended in a distant giant planet reveal how atmospheres outside the Solar System can form clouds very different from those on Earth, with mineral particles detected by light filtered during the transit of WASP-17 b in front of its star.
The James Webb Space Telescope identified signs of quartz nanocrystals in the high clouds of WASP-17 b, a gas giant located about 1,300 light-years from Earth and classified as a hot Jupiter.
The detection, made with data from the MIRI instrument, marks the first identification of silica particles in an exoplanet atmosphere, according to NASA.
The discovery is noteworthy because it shows that clouds outside the Solar System can have compositions very different from those observed on Earth.
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Instead of water droplets or ice crystals, the upper layers of this planet carry extremely small mineral particles, suspended in an atmosphere subjected to high temperatures.
WASP-17 b is not a rocky planet nor does it have a known surface like Earth’s.
It is a gaseous world, very voluminous and low-density, that orbits close to its star and, therefore, receives intense radiation capable of shaping an unusual atmosphere.
Crystals in clouds of a hot Jupiter
The detected crystals are formed by silicon dioxide, also called silica, in the crystalline form known as quartz.
In practice, the material is associated with the same mineral found on Earth, but appears in WASP-17 b as nanometric particles scattered high in the atmosphere.
According to NASA, the identified grains are about 10 nanometers in diameter, a scale so small that thousands of them could fit side by side in the thickness of a human hair.
Even so, in large quantities, these particles leave detectable marks in the light analyzed by Webb.
The presence of quartz does not mean that the planet has solid landscapes covered by the mineral, as could occur on a rocky surface.
What the data indicate is the existence of mineral aerosols in high clouds, floating in a gaseous layer with no direct parallel to terrestrial meteorology.
On Earth, common clouds form when water vapor condenses into liquid droplets or ice crystals.
In WASP-17 b, the conditions are extreme enough to allow another type of formation, based on mineral particles that interact with the light of the host star.
How the James Webb detected quartz
The observation was made when WASP-17 b passed in front of its star, in a phenomenon known as transit.
In this situation, part of the starlight passes through the planet’s atmosphere before reaching the telescope, carrying chemical signals left by gases, particles, and clouds.
The MIRI instrument, short for Mid-Infrared Instrument, recorded variations in this light at specific wavelengths.
According to NASA, the Webb observed the system for nearly ten hours and collected more than 1,275 measurements during the planet’s passage.
This type of analysis is called transmission spectroscopy and allows the investigation of distant atmospheres without photographing the planet as a detailed disk.
When a certain substance absorbs part of the radiation, it leaves a signature on the spectrum, comparable to a chemical fingerprint.
In the case of WASP-17 b, the signature was associated with crystalline silica.
The European Space Agency reported that the spectrum obtained by Webb on March 12 and 13, 2023, revealed the first evidence of quartz in the clouds of an exoplanet.
Why the discovery matters
The identification of silica in WASP-17 b broadens the understanding of the variety of clouds that can exist on planets outside the Solar System.
Atmospheric models already predicted the presence of minerals in very hot worlds, but the detection of quartz helps to better detail this composition.
In other exoplanets, scientists consider the possibility of clouds formed by silicates and other particles resistant to high temperatures.
The observation of quartz crystals shows that the chemistry of these atmospheres can be more specific than previously imagined.
These clouds also influence the reading of other atmospheric components.
Suspended particles can block, scatter, or alter the light passing through the planet, making it difficult to identify gases such as water vapor, carbon dioxide, and other relevant compounds.
Therefore, understanding the type of cloud present on an exoplanet is as important as detecting molecules in the atmosphere.
Without this information, the models used to interpret the spectra can overestimate or underestimate the presence of substances in different gaseous layers.
WASP-17 b as a natural laboratory
WASP-17 b belongs to the group of hot Jupiters, giant gaseous planets that orbit very close to their stars.
This proximity creates inflated atmospheres, high temperatures, and physical processes that have no direct equivalent in the more familiar planets of the Solar System.
Although not considered a candidate for harboring life, this type of world functions as a natural laboratory to test models on atmospheric circulation, cloud formation, and the interaction between stellar radiation and suspended particles.
Each observation helps to compare planets that are very different from each other.
The Webb plays a central role in this advancement because it observes the universe primarily in the infrared, a light range suitable for investigating molecules and particles that are cold or barely visible in other wavelengths.
In the study of WASP-17 b, the mid-infrared was decisive in distinguishing the signature of quartz.
The discovery also shows how the word “cloud” changes in meaning when applied to other worlds.
Outside Earth, they can be made of minerals, metals, or compounds that would never form common clouds in an atmosphere like Earth’s.
The case of WASP-17 b does not reveal a landscape photographed directly, but an atmosphere reconstructed from light.
The scientific image is of a giant, overheated, and distant planet, with high clouds carried by microscopic quartz crystals.
The detection reinforces that exoplanet atmospheres can hide unexpected compositions, even in worlds already known to astronomers.
At 1,300 light-years away, WASP-17 b shows that seemingly familiar phenomena, like clouds, can take on completely different forms in other planetary systems.
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