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Clouds are prevalent in many of the exoplanet atmospheres that have been observed to date. For transiting exoplanets, we know if clouds are present because they mute spectral features and cause wavelength-dependent scattering. While the exact composition of these clouds is largely unknown, this information is vital to understanding the chemistry and energy budget of planetary atmospheres. In this work, we observe one transit of the hot Jupiter WASP-17b with JWST’s Mid-Infrared Instrument Low Resolution Spectrometer and generate a transmission spectrum from 5 to 12 μm. These wavelengths allow us to probe absorption due to the vibrational modes of various predicted cloud species. Our transmission spectrum shows additional opacity centered at 8.6 μm, and detailed atmospheric modeling and retrievals identify this feature as SiO2(s) (quartz) clouds. The SiO2(s) clouds model is preferred at 3.5–4.2σ versus a cloud-free model and at 2.6σ versus a generic aerosol prescription. We find the SiO2(s) clouds are composed of small ∼0.01 μm particles, which extend to high altitudes in the atmosphere. The atmosphere also shows a depletion of H2O, a finding consistent with the formation of high-temperature aerosols from oxygen-rich species. This work is part of a series of studies by our JWST Telescope Scientist Team (JWST-TST), in which we will use Guaranteed Time Observations to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS).

The Gemini Planet Imager is a dedicated facility for directly imaging and spectroscopically characterizing extrasolar planets. It combines a very high-order adaptive optics system, a diffraction-suppressing coronagraph, and an integral field spectrograph with low spectral resolution but high spatial resolution. Every aspect of the Gemini Planet Imager has been tuned for maximum sensitivity to faint planets near bright stars. During first-light observations, we achieved an estimated H band Strehl ratio of 0.89 and a 5-σ contrast of 10 ⁶ at 0.75 arcseconds and 10 ⁵ at 0.35 arcseconds. Observations of Beta Pictoris clearly detect the planet, Beta Pictoris b, in a single 60-s exposure with minimal postprocessing. Beta Pictoris b is observed at a separation of 434 ± 6 milliarcseconds (mas) and position angle 211.8 ± 0.5°. Fitting the Keplerian orbit of Beta Pic b using the new position together with previous astrometry gives a factor of 3 improvement in most parameters over previous solutions. The planet orbits at a semimajor axis of [Formula] near the 3:2 resonance with the previously known 6-AU asteroidal belt and is aligned with the inner warped disk. The observations give a 4% probability of a transit of the planet in late 2017.

Gravitational deflection of starlight around the Sun during the 1919 total solar eclipse provided measurements that confirmed Einstein’s general theory of relativity. We have used the Hubble Space Telescope to measure the analogous process of astrometric microlensing caused by a nearby star, the white dwarf Stein 2051 B. As Stein 2051 B passed closely in front of a background star, the background star’s position was deflected. Measurement of this deflection at multiple epochs allowed us to determine the mass of Stein 2051 B—the sixth-nearest white dwarf to the Sun—as 0.675 ± 0.051 solar masses. This mass determination provides confirmation of the physics of degenerate matter and lends support to white dwarf evolutionary theory.

It has been suggested that β Pic b has a supersolar metallicity and subsolar C/O ratio. Assuming solar carbon and oxygen abundances for the star β Pic and therefore the planet’s parent protoplanetary disk, β Pic b’s C/O ratio suggests that it formed via core accretion between its parent protoplanetary disk’s H2O and CO2 ice lines. However, β Pic b’s high metallicity is difficult to reconcile with its mass M p = 11.7 M Jup. Massive stars can present peculiar photospheric abundances that are unlikely to record the abundances of their former protoplanetary disks. This issue can be overcome for early-type stars in moving groups by inferring the elemental abundances of the FGK stars in the same moving group that formed in the same molecular cloud and presumably share the same composition. We infer the photospheric abundances of the F dwarf HD 181327, a β Pic moving group member that is the best available proxy for the composition of β Pic b’s parent protoplanetary disk. In parallel, we infer updated atmospheric abundances for β Pic b. As expected for a planet of its mass formed via core-accretion beyond its parent protoplanetary disk’s H2O ice line, we find that β Pic b’s atmosphere is consistent with stellar metallicity and confirm that it has superstellar carbon and oxygen abundances with a substellar C/O ratio. We propose that the elemental abundances of FGK dwarfs in moving groups can be used as proxies for the otherwise difficult-to-infer elemental abundances of early-type and late-type members of the same moving groups.

Direct imaging observations are biased toward wide-separation, massive companions that have degenerate formation histories. Although the majority of exoplanets are expected to form via core accretion, most directly imaged exoplanets have not been convincingly demonstrated to follow this formation pathway. We obtained new interferometric observations of the directly imaged giant planet AF Lep b with the VLTI/GRAVITY instrument. We present three epochs of ∼50 μas relative astrometry and the K-band spectrum of the planet for the first time at a resolution of R = 500. Using only these measurements, spanning less than 2 months, and the Hipparcos-Gaia Catalogue of Accelerations, we are able to significantly constrain the planet’s orbit; this bodes well for interferometric observations of planets discovered by Gaia DR4. Including all available measurements of the planet, we infer an effectively circular orbit (e < 0.02, 0.07, and 0.13 at 1σ, 2σ, and 3σ, respectively) in spin–orbit alignment with the host and measure a dynamical mass of M p = 3.75M Jup ± 0.5M Jup. Models of the spectrum of the planet show that it is metal-rich ([M/H] = 0.75 ± 0.25), with a C/O abundance encompassing the solar value. This ensemble of results shows that the planet is consistent with core accretion formation.

Age-benchmark brown dwarf and planetary-mass-object spectroscopy is key to characterizing substellar evolution. In this paper, we present the JHK medium-resolution (R ∼ 3000) spectra of 25 7–76 MJup (spectral types L3.0–M6.0) brown dwarfs and planetary mass objects in the Orion Nebula Cluster, obtained with MOSFIRE installed at the W. M. Keck I telescope. We obtained the spectral types of the targets in our sample using template brown dwarf and planetary-mass-object spectra. We confirmed their extreme youth (<5 Myr) and membership of the cluster using spectral indices as well as the diversity of their spectra, even for targets with similar spectral types. Six of our targets presented Paschen β and Brackett γ emission lines, suggesting the existence of accreting protoplanetary disks for objects with masses as low as 7 MJup. After analyzing the emission lines of those objects, and measuring their accretion rates, we compared them to those of stars, brown dwarfs, and planetary mass objects, confirming that planetary mass young objects deplete their disks quickly at young ages. Finally, we illustrate the spectral evolution of a 7–10 MJup planetary mass object through its life from 1–3 to 200 Myr old, using one of our latest spectral type targets and other targets from the literature with older ages but similar estimated masses. The spectra are publicly available for the community’s use as data behind the figures.

We develop and disseminate effective point-spread functions and geometric-distortion solutions for high-precision astrometry and photometry with the JWST NIRISS instrument. We correct field dependencies and detector effects, and assess the quality and the temporal stability of the calibrations. As a scientific application and validation, we study the proper motion (PM) kinematics of stars in the JWST calibration field near the Large Magellanic Cloud (LMC) center, comparing to a first-epoch Hubble Space Telescope (HST) archival catalog with a 16 yr baseline. For stars with G ∼ 20, the median PM uncertainty is ∼13 μas yr−1 (3.1 km s−1), better than Gaia DR3 typically achieves for its very best-measured stars. We kinematically detect the known star cluster OGLE-CL LMC 407, measure its absolute PM for the first time, and show how this differs from other LMC populations. The inferred cluster dispersion sets an upper limit of 24 μas yr−1 (5.6 km s−1) on systematic uncertainties. Red-giant-branch stars have a velocity dispersion of 33.8 ± 0.6 km s−1, while younger blue populations have a narrower velocity distribution, but with a significant kinematical substructure. We discuss how this relates to the larger velocity dispersions inferred from Gaia DR3. These results establish JWST as capable of state-of-the-art astrometry, building on the extensive legacy of HST. This is the first paper in a series by our JWST Telescope Scientist Team, in which we will use Guaranteed Time Observations to study the PM kinematics of various stellar systems in the Local Group.

We present JWST MIRI Medium Resolution Spectrograph (MRS) observations of the β Pictoris system. We detect an infrared excess from the central unresolved point source from 5 to 7.5 μm which is indicative of dust within the inner ∼7 au of the system. We perform point-spread function (PSF) subtraction on the MRS data cubes and detect a spatially resolved dust population emitting at 5 μm. This spatially resolved hot dust population is best explained if the dust grains are in the small grain limit (2πa ≪ λ). The combination of unresolved and resolved dust at 5 μm could suggest that dust grains are being produced in the inner few astronomical units of the system and are then radiatively driven outwards, where the particles could accrete onto the known planets in the system, β Pictoris b and c. We also report the detection of an emission line at 6.986 μm that we attribute to [Ar ii]. We find that the [Ar ii] emission is spatially resolved with JWST and appears to be aligned with the dust disk. Through PSF-subtraction techniques, we detect β Pictoris b at the 5σ level in our MRS data cubes and present the first mid-infrared spectrum of the planet from 5 to 7 μm. The planet’s spectrum is consistent with having absorption from water vapor between 5 and 6.5 μm. We perform atmosphere model grid fitting of the spectra and photometry of β Pictoris b and find that the planet’s atmosphere likely has a substellar C/O ratio.

High-contrast observations with JWST can reveal key composition and vertical mixing dependent absorption features in the spectra of directly imaged planets across the 3–5 μm wavelength range. We present novel coronagraphic images of the HR 8799 and 51 Eri planetary systems using the NIRCam Long Wavelength Bar in an offset “narrow” position. These observations have revealed the four known gas giant planets encircling HR 8799, even at spatial separations challenging for a 6.5 m telescope in the mid-infrared, including the first ever detection of HR 8799 e at 4.6 μm. The chosen filters constrain the strength of CO, CH4, and CO2 absorption in each planet’s photosphere. The planets display a diversity of 3–5 μm colors that could be due to differences in composition and ultimately be used to trace their formation history. They also show stronger CO2 absorption than expected from solar metallicity models, indicating that they are metal enriched. We detected 51 Eri b at 4.1 μm and not at longer wavelengths, which, given the planet’s temperature, is indicative of out-of-equilibrium carbon chemistry and an enhanced metallicity. Updated orbits fit to the new measurement of 51 Eri b validate previous studies that find a preference for high eccentricities ( e=0.57−0.09+0.03 ), which likely indicates some dynamical processing in the system’s past. These results present an exciting opportunity to model the atmospheres and formation histories of these planets in more detail in the near future, and are complementary to future higher-resolution, continuum-subtracted JWST spectroscopy.

We have performed a comprehensive study of the Orion Nebula Cluster (ONC) combining the photometric data obtained by the two Hubble Space Telescope Treasury programs that targeted this region. To consistently analyze the rich data set obtained in a wide variety of filters, we adopted a Bayesian approach to fit the spectral energy distribution of the sources, deriving mass, age, extinction, distance, and accretion for each source in the region. The three-dimensional study of mass distribution for bona fide cluster members shows that mass segregation in the ONC extends to subsolar masses, while the age distribution strongly supports the idea that star formation in the ONC is best described by a major episode of star formation that happened ∼1 Myr ago. For masses ≳0.1 M ⊙, our derived empirical initial mass function (IMF) is in good agreement with a Chabrier system IMF. Both the accretion luminosity (L acc) and mass accretion rates ( Ṁacc ) are best described by broken power-law relations. This suggests that for the majority of young circumstellar disks in this cluster the excess emission may be dominated by X-ray-driven photoevaporation by the central star rather than external photoevaporation. If this is the case, the slopes of the power-law relations may be largely determined by the initial conditions set at the onset of the star formation process, which may be quite similar between regions that eventually form clusters of different sizes.