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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 R J (refs.  1,2 ), whose extended atmosphere is eroding 3 . 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 (SO 2 ) 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 SO 2 (refs.  8-10 ). Here we report the 9σ detection of two fundamental vibration bands of SO 2 , 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., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Brown dwarfs serve as ideal laboratories for studying the atmospheres of giant exoplanets on wide orbits, as the governing physical and chemical processes within them are nearly identical 1,2 . Understanding the formation of gas-giant planets is challenging, often involving the endeavour to link atmospheric abundance ratios, such as the carbon-to-oxygen (C/O) ratio, to formation scenarios 3 . However, the complexity of planet formation requires further tracers, as the unambiguous interpretation of the measured C/O ratio is fraught with complexity 4 . Isotope ratios, such as deuterium to hydrogen and 14 N/ 15 N, offer a promising avenue to gain further insight into this formation process, mirroring their use within the Solar System 5-7 . For exoplanets, only a handful of constraints on 12 C/ 13 C exist, pointing to the accretion of 13 C-rich ice from beyond the CO iceline of the disks 8,9 . Here we report on the mid-infrared detection of the 14 NH 3 and 15 NH 3 isotopologues in the atmosphere of a cool brown dwarf with an effective temperature of 380 K in a spectrum taken with the Mid-Infrared Instrument (MIRI) of JWST. As expected, our results reveal a 14 N/ 15 N value consistent with star-like formation by gravitational collapse, demonstrating that this ratio can be accurately constrained. Because young stars and their planets should be more strongly enriched in the 15 N isotope 10 , we expect that 15 NH 3 will be detectable in several cold, wide-separation exoplanets., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

The formation of stars and planets is accompanied not only by the build-up of matter, namely accretion, but also by its expulsion in the form of highly supersonic jets that can stretch for several parsecs 1,2 . As accretion and jet activity are correlated and because young stars acquire most of their mass rapidly early on, the most powerful jets are associated with the youngest protostars 3 . This period, however, coincides with the time when the protostar and its surroundings are hidden behind many magnitudes of visual extinction. Millimetre interferometers can probe this stage but only for the coolest components 3 . No information is provided on the hottest (greater than 1,000 K) constituents of the jet, that is, the atomic, ionized and high-temperature molecular gases that are thought to make up the jet's backbone. Detecting such a spine relies on observing in the infrared that can penetrate through the shroud of dust. Here we report near-infrared observations of Herbig-Haro 211 from the James Webb Space Telescope, an outflow from an analogue of our Sun when it was, at most, a few times 10 4 years old. These observations reveal copious emission from hot molecules, explaining the origin of the 'green fuzzies' 4-7 discovered nearly two decades ago by the Spitzer Space Telescope 8 . This outflow is found to be propagating slowly in comparison to its more evolved counterparts and, surprisingly, almost no trace of atomic or ionized emission is seen, suggesting its spine is almost purely molecular., (© 2023. The Author(s).)

Terrestrial and sub-Neptune planets are expected to form in the inner (less than 10 AU) regions of protoplanetary disks 1 . Water plays a key role in their formation 2-4 , although it is yet unclear whether water molecules are formed in situ or transported from the outer disk 5,6 . So far Spitzer Space Telescope observations have only provided water luminosity upper limits for dust-depleted inner disks 7 , similar to PDS 70, the first system with direct confirmation of protoplanet presence 8,9 . Here we report JWST observations of PDS 70, a benchmark target to search for water in a disk hosting a large (approximately 54 AU) planet-carved gap separating an inner and outer disk 10,11 . Our findings show water in the inner disk of PDS 70. This implies that potential terrestrial planets forming therein have access to a water reservoir. The column densities of water vapour suggest in-situ formation via a reaction sequence involving O, H 2 and/or OH, and survival through water self-shielding 5 . This is also supported by the presence of CO 2 emission, another molecule sensitive to ultraviolet photodissociation. Dust shielding, and replenishment of both gas and small dust from the outer disk, may also play a role in sustaining the water reservoir 12 . Our observations also reveal a strong variability of the mid-infrared spectral energy distribution, pointing to a change of inner disk geometry., (© 2023. The Author(s).)