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Carbon is an essential element for life but how much can be delivered to young planets is still an open question. The chemical characterization of planet-forming disks is a crucial step in our understanding of the diversity and habitability of exoplanets. Very low-mass stars (less than 0.2 M⊙) are interesting targets because they host a rich population of terrestrial planets. Here we present the James Webb Space Telescope detection of abundant hydrocarbons in the disk of a very low-mass star obtained as part of the Mid-InfraRed Instrument mid-INfrared Disk Survey (MINDS). In addition to very strong and broad emission from C2H2 and its 13C12CH2 isotopologue, C4H2, benzene and possibly CH4 are identified, but water, polycyclic aromatic hydrocarbons and silicate features are weak or absent. The lack of small silicate grains indicates that we can look deep down into this disk. These detections testify to an active warm hydrocarbon chemistry with a high C/O ratio larger than unity in the inner 0.1 astronomical units (AU) of this disk, perhaps due to destruction of carbonaceous grains. The exceptionally high C2H2/CO2 and C2H2/H2O column density ratios indicate that oxygen is locked up in icy pebbles and planetesimals outside the water iceline. This, in turn, will have important consequences for the composition of forming exoplanets.Highly abundant hydrocarbons in a very low-mass star’s disk are detected using the JWST. This unique chemical composition is probably due to the destruction of carbon grains, and the resulting high gaseous C/O ratio may have a profound impact on the composition of growing exoplanets.

Here, we show that the approximately 10-million-year-old β Pictoris system hosts a massive giant planet, β Pictoris b, located 8 to 15 astronomical units from the star. This result confirms that gas giant planets form rapidly within disks and validates the use of disk structures as fingerprints of embedded planets. Among the few planets already imaged, β Pictoris b is the closest to its parent star. Its short period could allow for recording of the full orbit within 17 years.

The imaging channel on the Mid-Infrared Instrument (MIRI) is equipped with four coronagraphs that provide high-contrast imaging capabilities for studying faint point sources and extended emission that would otherwise be overwhelmed by a bright point-source in its vicinity. Such targets might include stars that are orbited by exoplanets and circumstellar material, mass-loss envelopes around post-main-sequence stars, the near-nuclear environments in active galaxies, and the host galaxies of distant quasars. This paper describes the coronagraphic observing modes of MIRI, as well as performance estimates based on measurements of the MIRI flight model during cryo-vacuum testing. A brief outline of coronagraphic operations is also provided. Finally, simulated MIRI coronagraphic observations of a few astronomical targets are presented for illustration.

We describe a new type of coronagraph, based on the principle of a phase mask as proposed by Roddier and Roddier a few years ago but using an original mask design found by one of us (D. R.), a four‐quadrant binary phase mask (0, π) covering the full field of view at the focal plane. The mutually destructive interferences of the coherent light from the main source produce a very efficient nulling. The computed rejection rate of this coronagraph appears to be very high since, when perfectly aligned and phase‐error free, it could in principle reduce the total amount of light from the bright source by a factor of 108, corresponding to a gain of 20 mag in brightness at the location of the first Airy ring, relative to the Airy peak. In the real world the gain is of course reduced by a strong factor, but nulling is still performing quite well, provided that the perturbation of the phase, for instance, due to the Earth’s atmosphere, is efficiently corrected by adaptive optics. We show from simulations that a detection at a contrast of 10 mag between a star and a faint companion is achievable in excellent conditions, while 8 mag appears routinely feasible. This coronagraph appears less sensitive to atmospheric turbulence and has a larger dynamic range than other recently proposed nulling techniques: the phase‐mask coronagraph (by Roddier and Roddier) or the Achromatic Interfero‐Coronagraph (by Gay and Rabbia). We present the principle of the four‐quadrant coronagraph and results of a first series of simulations. We compare those results with theoretical performances of other devices. We briefly analyze the different limitations in space or ground‐based observations, as well as the issue of manufacturing the device. We also discuss several ways to improve the detection of a faint companion around a bright object. We conclude that, with respect to previous techniques, an instrument equipped with this coronagraph should have better performance and even enable the imaging of extrasolar giant planets at a young stage, when coupled with additional cleaning techniques.

We present the first high‐contrast images obtained at the ESO Very Large Telescope using a four‐quadrant phase mask coronagraph. The two‐night commissioning was carried out in 2004 January on NACO, the near‐IR camera with adaptive optics at UT4. We evaluated the behavior of the coronagraph on a variety of astrophysical targets: binary stars, circumstellar disks, and active galactic nuclei. The performance of the coronagraph is in agreement with our expectations based on numerical simulations. The phase mask provides a stellar peak attenuation of a factor of about 10 on average (for long exposure), and its performance is limited only by the phase residuals (mainly low‐order aberrations) that are left uncorrected by the adaptive optics system.

The performance of high contrast imaging systems is very often limited by the presence of static speckles in the point-spread function of the central source. Several techniques have already been proposed to discriminate a faint companion from these residual speckles. These techniques used different criteria to separate a speckle from a companion: polarization, spectral information or coherence. Here, we propose a new imaging device, the Self-Coherent Camera (SCC), that is based on the lack of coherence between the stellar light and the planet that is searched for. This SCC is a simple instrument that allows us to reach the fundamental limitation of the photon noise by calibrating the speckles in the recorded images. After the description of the general problem of discriminating speckles from planets, we will explain the principle of the SCC. Then, we will analyze the different limitations of this technique as well as the performance that can be reached with current telescopes.

For a comprehensive understanding of planetary formation and evolution, we need to investigate the environment in which planets form: circumstellar disks. Here we present high-contrast imaging observations of V4046 Sagittarii, a 20-Myr-old close binary known to host a circumbinary disk. We have discovered the presence of rotating shadows in the disk, caused by mutual occultations of the central binary. Shadow-like features are often observed in disks1,2, but those found thus far have not been due to eclipsing phenomena. We have used the phase difference due to light travel time to measure the flaring of the disk and the geometrical distance of the system. We calculate a distance that is in very good agreement with the value obtained from the Gaia mission’s Data Release 2 (DR2), and flaring angles of α = (6.2 ± 0.6)° and α = (8.5 ± 1.0)° for the inner and outer disk rings, respectively. Our technique opens up a path to explore other binary systems, providing an independent estimate of distance and the flaring angle, a crucial parameter for disk modelling.Moving shadows have been seen on the circumbinary disk around V4046 Sgr, cast by eclipses of the central binary system. Using geometrical arguments, the degree of flaring of the disk and the distance to the system have been calculated.

In the first paper in this series, we described the principle of a coronagraph utilizing a four‐quadrant phase mask and the results of numerical simulations obtained in the perfect case. In this second paper, we performed additional numerical simulations to assess in more detail the performances and limitations of this coronagraph under real conditions. The effect of geometrical parameters such as shape and size of both the phase mask and the Lyot stop is studied. We also analyze the effect of low‐ and high‐order aberrations generated, for instance, by the atmospheric turbulence. An important issue is the wavelength dependence of the phase mask. We show that the performance decreases rapidly as the spectral bandwidth is increased, and as a consequence, we discuss the manufacturing of achromatized masks using multiple thin films. An optical concept is proposed.

We report a laboratory experiment to assess the performance and limitations of the four‐quadrant phase mask coronagraph we proposed 2 years ago. A total flux rejection factor of 4400 was reached using off‐the‐shelf optical components. The peak intensity of the Airy pattern is correspondingly reduced by a factor of 44,000 with a stability of a few hours. In this paper, we discuss implications of this excellent result regarding the next generation of instruments for extrasolar planet detection.

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.  Observations with the sensitive mid-infrared spectrometer MIRI on board JWST reveal the presence of a water vapour reservoir in the terrestrial plant-forming zone of the young planetary system PDS 70.