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- Dyrek, Achrène, et al.
(author)
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SO2, silicate clouds, but no CH4 detected in a warm Neptune
- 2024
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In: Nature. - 0028-0836 .- 1476-4687. ; 625, s. 51-54
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Journal article (peer-reviewed)abstract
- WASP-107b is a warm (approximately 740 K) transiting planet with a Neptune-like mass of roughly 30.5 M⊕ and Jupiter-like radius of about 0.94 RJ (refs. 1,2), whose extended atmosphere is eroding3. Previous observations showed evidence for water vapour and a thick, high-altitude condensate layer in the atmosphere of WASP-107b (refs. 4,5). Recently, photochemically produced sulfur dioxide (SO2) was detected in the atmosphere of a hot (about 1,200 K) Saturn-mass planet from transmission spectroscopy near 4.05 μm (refs. 6,7), but for temperatures below about 1,000 K, sulfur is predicted to preferably form sulfur allotropes instead of SO2 (refs. 8,9,10). Here we report the 9σ detection of two fundamental vibration bands of SO2, at 7.35 μm and 8.69 μm, in the transmission spectrum of WASP-107b using the Mid-Infrared Instrument (MIRI) of JWST. This discovery establishes WASP-107b as the second irradiated exoplanet with confirmed photochemistry, extending the temperature range of exoplanets exhibiting detected photochemistry from about 1,200 K down to about 740 K. Furthermore, our spectral analysis reveals the presence of silicate clouds, which are strongly favoured (around 7σ) over simpler cloud set-ups. Furthermore, water is detected (around 12σ) but methane is not. These findings provide evidence of disequilibrium chemistry and indicate a dynamically active atmosphere with a super-solar metallicity.
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| 2. |
- Martin-Lagarde, Marine, et al.
(author)
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Magrathea : A proposal for a satellite mission on protoplanetary dust growth experiments
- 2018
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In: IAC-18. - : International Astronautical Federation.
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Conference paper (peer-reviewed)abstract
- The process of planet formation, from dust to protoplanetary disks, is not very well understood. The physics of both particle growth in protoplanetary disks and small particle dust gravity dynamics are well studied. However, the link between the two, i.e. the growth gap between dust grains and mm-sized particles, is still not understood. Additionally, current methods cannot model the full complexity of interactions in this phase of planet formation. Therefore, experiments in microgravity are crucial to revealing the underlying physics. Previous experiments have several limitations in particular their short duration and constrained dimensions. Accurately representing the conditions in the protoplanetary disk, such as the dust particle mean free path and large spatial extent of the dust, is very demanding, especially with larger, longer duration experiments.In order to create the best conditions for these experiments to be scientifically sound, with a reasonable solution, here we present a concept satellite with a 6 m3 chamber. The payload bay provides different measurements of ongoing collision processes, and samples of collision products. Its modularity and capacity is designed to carry several instruments in a carrousel, with 28 experiment canisters. Those experiments have a range of compositions (including silicates and Fayalite, both with or without ice layers), size distribution (between 1 µm and 100 mm), and shape properties, probing the conditions that could benefit grain growth. Each experiment will last up to one month allowing the record of approximately 106 collisions, with relative velocities of up to 5 mm/s, obtaining statistically meaningful results.With the science objectives and requirements formulated, payload solutions were prepared, and a conceptual mission and spacecraft design was developed. Considering the experiment phase will last up to 5 years, and during that time external influences should be minimised, the three most complex systems are the structure, thermal control, and attitude control. After several trade-offs and a cost analysis, a 1000 kg spacecraft solution was reached, set on a 800 km Sun-synchronous orbit. The mission would cost around 438 M Euros.The full work was developed during the 10 days of the 2017 Alpbach Summer School, by a group of fifteen young scientists and engineers, with various backgrounds, from all across Europe, with the support of two dedicated tutors. A concurrent engineering approach, with participants divided among several teams has been used to evaluate more than one scenario, and thus reach a concise solution.
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