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Owing to their similarities with giant exoplanets, brown dwarf companions of stars provide insights into the fundamental processes of planet formation and evolution. From their orbits, several brown dwarf companions are found to be more massive than theoretical predictions given their luminosities and the ages of their host stars 1 – 3 . Either the theory is incomplete or these objects are not single entities. For example, they could be two brown dwarfs each with a lower mass and intrinsic luminosity 1 , 4 . The most problematic example is Gliese 229 B (refs.  5 , 6 ), which is at least 2–6 times less luminous than model predictions given its dynamical mass of 71.4 ± 0.6 Jupiter masses ( M Jup ) (ref.  1 ). We observed Gliese 229 B with the GRAVITY interferometer and, separately, the CRIRES+ spectrograph at the Very Large Telescope. Both sets of observations independently resolve Gliese 229 B into two components, Gliese 229 Ba and Bb, settling the conflict between theory and observations. The two objects have a flux ratio of 0.47 ± 0.03 at a wavelength of 2 μm and masses of 38.1 ± 1.0 and 34.4 ± 1.5  M Jup , respectively. They orbit each other every 12.1 days with a semimajor axis of 0.042 astronomical units ( au ). The discovery of Gliese 229 BaBb, each only a few times more massive than the most massive planets, and separated by 16 times the Earth–moon distance, raises new questions about the formation and prevalence of tight binary brown dwarfs around stars. Analysis of the cool brown dwarf Gliese 229 B suggests that it is actually a close binary of two less massive brown dwarfs, explaining its low luminosity and settling the conflict between theoretical predictions and measurements.

The atmospheres of the giant planets are reducing, being mainly composed of hydrogen, helium and methane. But the rings and icy satellites that surround these planets, together with the flux of interplanetary dust, could act as important sources of oxygen, which would be delivered to the atmospheres mainly in the form of water ice or silicate dust 1 , 2 , 3 , 4 , 5 , 6 , 7 . Here we report the detection, by infrared spectroscopy, of gaseous H 2 O in the upper atmospheres of Saturn, Uranus and Neptune. The implied H 2 O column densities are 1.5 × 10 15 , 9× 10 13 and 3× 10 14 molecules cm −2 respectively. CO 2 in comparable amounts was also detected in the atmospheres of Saturn and Neptune. These observations can be accounted for by external fluxes of 10 5 –10 7 H 2 O molecules cm −2 s −1 and subsequent chemical processing in the atmospheres. The presence of gaseous water and infalling dust will affect the photochemistry, energy budget and ionospheric properties of these atmospheres. Moreover, our findings may help to constrain the injection rate and possible activity of distant icy objects in the Solar System.

Water In Star-forming regions with Herschel (WISH) is a key program on the Herschel Space Observatory designed to probe the physical and chemical structures of young stellar objects using water and related molecules and to follow the water abundance from collapsing clouds to planet-forming disks. About 80 sources are targeted, covering a wide range of luminosities-from low (< 1) to high (>10)-and a wide range of evolutionary stages-from cold prestellar cores to warm protostellar envelopes and outflows to disks around young stars. Both the HIFI and PACS instruments are used to observe a variety of lines of HO , HO and chemically related species at the source position and in small maps around the protostars and selected outflow positions. In addition, high-frequency lines of CO, CO , and CO are obtained with Herschel and are complemented by ground-based observations of dust continuum, HDO, CO and its isotopologs, and other molecules to ensure a self-consistent data set for analysis. An overview of the scientific motivation and observational strategy of the program is given, together with the modeling approach and analysis tools that have been developed. Initial science results are presented. These include a lack of water in cold gas at abundances that are lower than most predictions, strong water emission from shocks in protostellar environments, the importance of UV radiation in heating the gas along outflow walls across the full range of luminosities, and surprisingly widespread detection of the chemically related hydrides OH and HO in outflows and foreground gas. Quantitative estimates of the energy budget indicate that HO is generally not the dominant coolant in the warm dense gas associated with protostars. Very deep limits on the cold gaseous water reservoir in the outer regions of protoplanetary disks are obtained that have profound implications for our understanding of grain growth and mixing in disks.

Water features in old stars The discovery in 2001 of water vapour around the ageing carbon star IRC+10216 was a surprise, because stellar evolution models predicted the virtual absence of water in carbon-rich stars. Several explanations were offered, but with only one water line detected in the spectrum of one carbon-rich evolved star, it was difficult to discriminate between the alternatives. Now observations with the European Space Agency's Herschel satellite have discovered dozens of water lines in the far-infrared and submillimetre spectrum of IRC+10216. These include high-excitation lines with energies corresponding to temperatures of around 1,000 K, which can be explained only if water is present in the warm inner sooty region of the envelope. Water has been predicted to be almost absent in carbon-rich stars, so the detection of water vapour around the ageing carbon star IRC + 10216 challenged our understanding of the chemistry in old stars. Several explanations for the water have been postulated, but with only one water line detected it is difficult to discriminate between them. Now, dozens of water vapour lines have been detected in the far-infrared and sub-millimetre spectrum of IRC + 10216. The detection 1 of circumstellar water vapour around the ageing carbon star IRC +10216 challenged the current understanding of chemistry in old stars, because water was predicted 2 to be almost absent in carbon-rich stars. Several explanations for the water were postulated, including the vaporization of icy bodies (comets or dwarf planets) in orbit around the star 1 , grain surface reactions 3 , and photochemistry in the outer circumstellar envelope 4 . With a single water line detected so far from this one carbon-rich evolved star, it is difficult to discriminate between the different mechanisms proposed. Here we report the detection of dozens of water vapour lines in the far-infrared and sub-millimetre spectrum of IRC +10216 using the Herschel satellite 5 . This includes some high-excitation lines with energies corresponding to ∼1,000 K, which can be explained only if water is present in the warm inner sooty region of the envelope. A plausible explanation for the warm water appears to be the penetration of ultraviolet photons deep into a clumpy circumstellar envelope. This mechanism also triggers the formation of other molecules, such as ammonia, whose observed abundances 6 are much higher than hitherto predicted 7 .

Water In Star-forming regions withHerschel(WISH) is a key program on theHerschel Space Observatorydesigned to probe the physical and chemical structures of young stellar objects using water and related molecules and to follow the water abundance from collapsing clouds to planet-forming disks. About 80 sources are targeted, covering a wide range of luminosities—from low (< 1 L ⊙ < 1     L ⊙ ) to high (>105 L ⊙ > 10 5     L ⊙ )—and a wide range of evolutionary stages—from cold prestellar cores to warm protostellar envelopes and outflows to disks around young stars. Both the HIFI and PACS instruments are used to observe a variety of lines ofH2O H 2 O ,H2 18O H 2 O 18 and chemically related species at the source position and in small maps around the protostars and selected outflow positions. In addition, high-frequency lines of CO, 13CO CO 13 , andC18O C O 18 are obtained withHerscheland are complemented by ground-based observations of dust continuum, HDO, CO and its isotopologs, and other molecules to ensure a self-consistent data set for analysis. An overview of the scientific motivation and observational strategy of the program is given, together with the modeling approach and analysis tools that have been developed. Initial science results are presented. These include a lack of water in cold gas at abundances that are lower than most predictions, strong water emission from shocks in protostellar environments, the importance of UV radiation in heating the gas along outflow walls across the full range of luminosities, and surprisingly widespread detection of the chemically related hydridesOH+ OH + andH2O+ H 2 O + in outflows and foreground gas. Quantitative estimates of the energy budget indicate thatH2O H 2 O is generally not the dominant coolant in the warm dense gas associated with protostars. Very deep limits on the cold gaseous water reservoir in the outer regions of protoplanetary disks are obtained that have profound implications for our understanding of grain growth and mixing in disks.

Protoplanetary disks around young Sun-like stars are the cradles of the vast majority of detected exoplanets. Probing these disks at multiple spatial scales is key to uncovering how planets form. We aim to spatially and spectrally resolve the inner disk and star-disk interaction region of the M0.3 T Tauri star DO Tau by combining two complementary techniques. We used high-resolution near-infrared spectra from CFHT/SPIRou to constrain the magnetospheric star-disk interaction process and optical long-baseline interferometry with ESO VLTI/GRAVITY to determine the sizes of the K-band continuum and Br\\(\\gamma\\) line emitting regions. From the SPIRou spectra, we confirmed that this ~0.5 M\\(_\\odot\\) star is a strong accretor. The HI and HeI lines exhibit strong variability on a daily timescale, consistent with the burster classification of DO Tau derived from its K2 light curve. We derived an upper limit of 0.35 on the ratio between the magnetospheric truncation radius and the disk corotation radius, indicative of an ordered unstable accretion regime. The size of the Br\\(\\gamma\\) line emitting region obtained from GRAVITY is much smaller than the K-band continuum emitting region. This compact Br\\(\\gamma\\) emission region (\\(R_{Br\\gamma} \\sim\\) 0.011 au) suggests that most of the line flux originates from the magnetospheric accretion region and/or from an inner wind close to the magnetosphere-disk interface. The inclination we derived for the inner disk (45-55{\\deg}) differs from that of the outer disk inferred from the ALMA continuum (30{\\deg}). This points toward a misalignment or warp of the outer disk that may originate from the suspected past encounter with the neighboring HV Tau system.

Aims: The presence of a Yukawa-like correction to Newtonian gravity is investigated at the Galactic Center, leading to a new upper limit for the intensity of such a correction. Methods: We perform a Markov Chain Monte Carlo analysis using the astrometric and spectroscopic data of star S\\(2\\) collected at the Very Large Telescope by GRAVITY, NACO and SINFONI instruments, covering the period from \\(1992\\) to \\(2022\\). Results: The precision of the GRAVITY instrument allows us to derive the most stringent upper limit at the Galactic Center for the intensity of the Yukawa contribution (\\(\\propto \\, \\alpha e^{- \\lambda r}\\)) to be \\(|\\alpha| < 0.003\\) for a scale length \\(\\lambda = 3 \\cdot 10^{13}\\, \\rm m\\, (\\sim 200 \\, \\rm AU)\\). This improves by roughly one order of magnitude all estimates obtained in previous works.

Direct astrometric detection of exomoons remains unexplored. This study presents the first application of high-precision astrometry to search for exomoons around substellar companions. We investigate whether the orbital motion of the companion HD 206893 B exhibits astrometric residuals consistent with the gravitational influence of an exomoon or binary planet. Using the VLTI/GRAVITY instrument, we monitored the astrometric positions of HD 206893 B and c across both short (days to months) and long (yearly) timescales. This enabled us to isolate potential residual wobbles in the motion of component B attributable to an orbiting moon. Our analysis reveals tentative astrometric residuals in the HD 206893 B orbit. If interpreted as an exomoon signature, these residuals correspond to a candidate (HD 206893 B I) with an orbital period of approximately 0.76 years and a mass of \\(\\sim\\)0.4 Jupiter masses. However, the origin of these residuals remains ambiguous and could be due to systematics. Complementing the astrometry, our analysis of GRAVITY \\(R=4000\\) spectroscopy for HD 206893 B confirms a clear detection of water, but no CO is found using cross-correlation. We also find that AF Lep b, and \\(\\beta\\) Pic b are the best short-term candidates to look for moons with GRAVITY+. Our observations demonstrate the transformative potential of high-precision astrometry in the search for exomoons, and proves the feasibility of the technique to detect moons with masses lower than Jupiter and potentially down to less than Neptune in optimistic cases. Crucially, further high-precision astrometric observations with VLTI/GRAVITY are essential to verify the reality and nature of this signal and attempt this technique on a variety of planetary systems.

The dust- and gas-rich protoplanetary disks around young stellar systems play a key role in star and planet formation. While considerable progress has recently been made in probing these disks on large scales of a few tens of astronomical units (au), the central au needs to be more investigated. We aim at unveiling the physical processes at play in the innermost regions of the strongly accreting T Tauri Star S CrA N by means of near-infrared interferometric observations. The K-band continuum emission is well reproduced with an azimuthally-modulated dusty ring. As the star alone cannot explain the size of this sublimation front, we propose that magnetospheric accretion is an important dust-heating mechanism leading to this continuum emission. The differential analysis of the Hydrogen Br\\(\\) line is in agreement with radiative transfer models combining magnetospheric accretion and disk winds. Our observations support an origin of the Br\\(\\) line from a combination of (variable) accretion-ejection processes in the inner disk region.

The ionisation cones of NGC5728 have a deficit of molecular gas based on millimetre observations of CO(2-1) emission. Although photoionisation from the active nucleus may lead to suppression of this transition, warm molecular gas can still be present. We report the detection of eight mid-infrared rotational H\\(_2\\) lines throughout the central kiloparsec, including the ionisation cones, using integral field spectroscopic observations with JWST/MIRI MRS. The H\\(_2\\) line ratios, characteristic of a power-law temperature distribution, indicate that the gas is warmest where it enters the ionisation cone through disk rotation, suggestive of shock excitation. In the nucleus, where the data can be combined with an additional seven ro-vibrational H\\(_2\\) transitions, we find that moderate velocity (30 km s\\(^{-1}\\)) shocks in dense (\\(10^5\\) cm\\(^{-3}\\)) gas, irradiated by an external UV field (\\(G_0 = 10^3\\)), do provide a good match to the full set. The warm molecular gas in the ionisation cone that is traced by the H\\(_2\\) rotational lines has been heated to temperatures \\(>200\\) K. Outside of the ionisation cone the molecular gas kinematics are undisturbed. However, within the ionisation cone, the kinematics are substantially perturbed, indicative of a radial flow, but one that is quantitatively different from the ionised lines. We argue that this outflow is in the plane of the disk, implying a short 50 pc acceleration zone up to speeds of about 400 km s\\(^{-1}\\) followed by an extended deceleration over \\(\\sim\\)700 pc where it terminates. The deceleration is due to both the radially increasing galaxy mass, and mass-loading as ambient gas in the disk is swept up.