Artist impression of WASP-107b and its
parent star. Credit: Illustration: LUCA School of Arts, Belgium/ Klaas Verpoest
(visuals), Johan Van Looveren (typography). Science: Achrène Dyrek (CEA and
Université Paris Cité, France), Michiel Min (SRON, the Netherlands), Leen Decin
(KU Leuven, Belgium) / European MIRI EXO GTO team / ESA / NASA
A
team of European astronomers, co-led by researchers from the Institute of
Astronomy, KU Leuven, used recent observations made with the James Webb Space
Telescope to study the atmosphere of the nearby exoplanet WASP-107b. Peering
deep into the fluffy atmosphere of WASP-107b they discovered not only water
vapor and sulfur dioxide, but even silicate sand clouds. These particles reside
within a dynamic atmosphere that exhibits vigorous transport of material.
Astronomers worldwide are harnessing the
advanced capabilities of the Mid-Infrared Instrument (MIRI) aboard the James
Webb Space Telescope (JWST) to conduct groundbreaking observations of
exoplanets—planets orbiting stars other than our own sun. One of these
fascinating worlds is WASP-107b, a unique gaseous exoplanet that orbits a star
slightly cooler and less massive than our sun.
The mass of the planet is similar to that of Neptune but its size is much larger than that of Neptune, almost approaching the size of Jupiter. This characteristic renders WASP-107b rather 'fluffy' when compared to the gas giant planets within our solar system. The fluffiness of this exoplanet enables astronomers to look roughly 50 times deeper into its atmosphere compared to the depth of exploration achieved for a solar-system giant like Jupiter.
WASP-107b is a unique gaseous exoplanet that
orbits a star slightly cooler and less massive than our sun. The mass of the
planet is similar to that of Neptune but its size is much larger than that of
Neptune, almost approaching the size of Jupiter. This characteristic renders
WASP-107b rather 'fluffy' when compared to the gas giant planets within our
solar system. The fluffiness of this exoplanet enables astronomers to look
roughly 50 times deeper into its atmosphere compared to the depth of
exploration achieved for a solar-system giant like Jupiter. Credit:
Illustration: LUCA School of Arts, Belgium/ Klaas Verpoest (visuals), Johan Van
Looveren (typography). Science: Achrène Dyrek (CEA and Université Paris Cité,
France), Michiel Min (SRON, the Netherlands), Leen Decin (KU Leuven, Belgium) /
European MIRI EXO GTO team / ESA / NASA
The team of European astronomers
took full advantage of the remarkable fluffiness of this exoplanet, enabling
them to look deep into its atmosphere. This opportunity opened a window into
unraveling the complex chemical composition of its atmosphere.
The reason behind this is quite
straightforward: the signals, or spectral features, are far more prominent in a
less dense atmosphere compared to a more compact one. Their recent study, now
published in Nature, reveals the presence of water vapor, sulfur dioxide (SO2), and silicate clouds, but notably, there is no trace of the greenhouse
gas methane (CH4).
A dynamic atmosphere
These detections provide crucial
insights into the dynamics and chemistry of this captivating exoplanet. First,
the absence of methane hints at a potentially warm interior, offering a
tantalizing glimpse into the movement of heat energy in the planet's atmosphere.
Secondly, the discovery of sulfur dioxide (known for the odor of burnt
matches), was a major surprise.
Previous models had predicted its absence, but novel climate models of WASP-107b's atmosphere now show that the very fluffiness of WASP-107b accommodates the formation of sulfur dioxide in its atmosphere. Even though its host star emits a relatively small fraction of high-energy photons due to its cooler nature, these photons can reach deep into the planet's atmosphere thanks to its fluffy nature. This enables the chemical reactions required to produce sulfur dioxide to occur.
A transmission spectrum of the warm Neptune exoplanet WASP-107b, captured by
the Low Resolution Spectrometer (LRS) of the Mid InfraRed Instrument (MIRI) on
board JWST, reveals evidence for water vapour, sulfur dioxide, and silicate
(sand) clouds in the planet's atmosphere. Credit: Michiel Min / European MIRI
EXO GTO team / ESA / NASA
But
that's not all they've observed. Both the spectral features of sulfur dioxide
and water vapor are significantly diminished compared to what they would be in
a cloudless scenario. High-altitude clouds partially obscure the water vapor
and sulfur dioxide in the atmosphere.
While clouds have been inferred on other
exoplanets, this marks the first instance where astronomers can definitively
identify the chemical composition of these clouds. In this case, the clouds
consist of small silicate particles, a familiar substance for humans found in
many parts of the world as the primary constituent of sand.
"JWST is revolutionizing exoplanet
characterization, providing unprecedented insights at remarkable speed,"
says lead author Prof. Leen Decin of KU Leuven. "The discovery of clouds
of sand, water, and sulfur dioxide on this fluffy exoplanet by JWST's MIRI
instrument is a pivotal milestone. It reshapes our understanding of planetary
formation and evolution, shedding new light on our own solar system."
In contrast to Earth's atmosphere, where water freezes at low temperatures, in gaseous planets reaching temperatures around 1000 degrees Celsius, silicate particles can freeze out to form clouds. However, in the case of WASP-107b, with a temperature of around 500 degrees Celsius in the outer atmosphere, traditional models predicted that these silicate clouds should be forming deeper within the atmosphere, where temperatures are substantially higher. In addition, sand clouds high up in the atmosphere rain out. How is it then possible that these sand clouds exist at high altitudes and continue to endure?
Peering deep into the fluffy atmosphere
of WASP-107b a team of European astronomers discovered not only water vapour
and sulfur dioxide, but even silicate sand clouds. Credit: Illustration: LUCA
School of Arts, Belgium/ Klaas Verpoest (visuals), Johan Van Looveren
(typography). Science: Achrène Dyrek (CEA and Université Paris Cité, France),
Michiel Min (SRON, the Netherlands), Leen Decin (KU Leuven, Belgium) / European
MIRI EXO GTO team / ESA / NASA
According to lead author Dr.
Michiel Min, "The fact that we see these sand clouds high up in the
atmosphere must mean that the sand rain droplets evaporate in deeper, very hot
layers and the resulting silicate vapor is efficiently moved back up, where
they recondense to form silicate clouds once more. This is very similar to the
water vapor and cloud cycle on our own Earth but with droplets made of
sand."
This continuous cycle of
sublimation and condensation through vertical transport is responsible for the
enduring presence of sand clouds in WASP-107b's atmosphere.
This pioneering research not only
sheds light on the exotic world of WASP-107b but also pushes the boundaries of
our understanding of exoplanetary atmospheres. It marks a significant milestone
in exoplanetary exploration, revealing the intricate interplay of chemicals and
climatic conditions on these distant worlds.
"JWST enables a deep
atmospheric characterization of an exoplanet that does not have any counterpart
in our solar system, we are unraveling new worlds," says lead author Dr.
Achrène Dyrek at CEA Paris.
Design and development of the MIRI instrument
Belgian engineers and scientists
played a key role in the design and development of the MIRI instrument,
including the Center Spatial de Liege (CSL), Thales Alenia Space (Charleroi)
and OIP Sensor Systems (Oudenaarde). At the Institute of Astronomy at KU
Leuven, instrument scientists tested the MIRI instrument extensively in special
test chambers simulating the space environment in laboratories in the UK, at
NASA Goddard and NASA Johnson Space centers.
"With colleagues across Europe
and the United States we have been building and testing the MIRI instrument for
almost 20 years. It is rewarding to see our instrument unravel the atmosphere of this intriguing exoplanet," says
instrument specialist Dr. Bart Vandenbussche of KU Leuven.
This study combines the results of several independent analyses of the JWST observations, and represents the years of work invested not only in building the MIRI instrument but also in the calibration and analysis tools for the observational data acquired with MIRI," says Dr. Jeroen Bouwman of the Max-Planck-Institut für Astronomie, Germany.
by KU Leuven
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