IREx Researchers Are Awarded Coveted Observing Time on the Webb Telescope For Cycle 5

The competition was fiercer than ever to obtain precious observing time on the James Webb Space Telescope during its Cycle 5 period which will begin in July 2026. The Space Telescope Science Institute received a record-breaking 2 935 observing proposals requesting over 100 000 hours of time… when only about 8 000 hours were up for grabs! This represents an over subscription rate of nearly 13 to 1, larger than any other telescope has ever seen.

On March 13, the results of this competition were finally announced, and several IREx researchers were awarded coveted time on the telescope for their research programs. Canadian astronomers all around also had a great showing, with 5% of all awarded time being given to Canadian Principal Investigators (PIs). This fraction rises to over 10% when including Canadian co-PIs.

Find out more about IREx researchers’ Cycle 5 JWST programs here:

Loïc Albert, researcher and the NIRISS Instrument Scientist at the Université de Montréal.

Program 9579: The Fate of Jovian Worlds
PI: Susan Mullally (STScI)
co-PI: Loïc Albert (UdeM)
Time awarded: 108.2h using MIRI/Imaging
Summary: This program aims to directly image a population of old, cold giant planets orbiting nearby white dwarfs using JWST’s mid-infrared capabilities. Because white dwarfs are not very bright, they provide favourable contrast for detecting sub-Jupiter mass planets a large distance from their host star The team will conduct a common proper motion survey of 30 nearby systems over multiple observing cycles, targeting orbital distances between 4 and 500 AU (1 AU being the distance between the Earth and the Sun). JWST’s sensitivity makes it possible, for the first time, to detect planetary systems similar to our Solar System in these environments, with sensitivity down to less than half a Jupiter mass for all targets and below Saturn mass for most. The planets targeted in this survey are expected to be 1 to 10 billion years old, making them significantly colder than most directly imaged exoplanets. The program will constrain how frequently Jupiter- and Saturn-like planets occur around white dwarfs, and more broadly how planetary systems evolve after their host stars dies. Any detections will provide a valuable sample of cold, mature planets for future atmospheric and orbital characterisation.

Érika Le Bourdais, Ph.D. student at the Université de Montréal.

Program 9833: Journey to the Edge of WD 1145+017’s Circumstellar Disk
PI: Érika Le Bourdais (UdeM)
Time awarded: 7.8h using MIRI/Imaging, MIRI/LRS and NIRSpec/FR
Summary: WD 1145+017 is a polluted white dwarf surrounded by a complex debris disk and an actively disintegrating planetesimal, offering a unique laboratory to study the final stages of planetary systems. The system shows an unusually high abundance of heavy elements in both its atmosphere and surrounding gas, indicating ongoing accretion from its circumstellar environment. This program will use JWST’s MIRI and NIRSpec instruments to characterise the thermal structure, spatial distribution, and mineral composition of the dust disk. In particular, the team will analyse key infrared features, such as the 10μm silicate band, to constrain the properties of the disk material. These observations will provide the first comprehensive view of the pollution process in a white dwarf system, from the outer edge of the circumstellar disk to the star’s photosphere. The results will improve our understanding of how planetary systems break down after stellar evolution, and offer insight into the composition of exoplanets’ material.

Thomas Vandal, Ph.D. student at the Université de Montréal.

Program 10110: Uncovering the coldest extra-solar worlds: a companion search down to 200K around the coolest brown dwarfs
PI: Clémence Fontanive (Edinburgh)
Co-PI: Thomas Vandal (UdeM)
Time awarded: 30.8h using NIRCam/Imaging
Summary: This program aims to explore the coldest known population of free-floating objects beyond our Solar System, known as Y dwarfs, which have temperatures below 500 degrees K. A significant gap remains between the coldest known Y dwarfs (~300 K) and Jupiter (~150 K), limiting our understanding of the transition between brown dwarfs and giant planets. Using JWST’s NIRCam, the team will conduct an imaging survey of 206 nearby late-type brown dwarfs within 20 parsecs of the Sun, searching for even colder companions down to ~200 K at separations of 1–3 AU. This sensitivity opens a previously unexplored region of parameter space, including low-mass companions and tightly bound systems that were inaccessible to earlier surveys. The program aims to identify new ultra-cold Y dwarfs, characterise their atmospheres, and discover benchmark binary systems suitable for dynamical mass measurements. Even a partial survey of the sample is expected to yield new discoveries or place strong constraints on the frequency of such objects. These observations will help bridge the gap between brown dwarfs and gas giant planets, improving models of atmospheric physics, formation, and evolution at the lowest masses.

Jared Splinter, Ph.D. student at McGill University.

Program 11301: Cloudy with a Chance of Disequilibrium Chemistry: A Comprehensive View of Silicate Clouds in a Hot Jupiter with a MIRI/LRS Phase Curve
PI: Jared Splinter (McGill University)
Time awarded: 69.5h using MIRI/LRS
Summary: This program will obtain a full-orbit phase curve of the hot Jupiter HD 189733 b using JWST’s MIRI Low Resolution Spectroscopy (LRS). Previous observations suggest that hot Jupiters exhibit a wide diversity in atmospheric properties, with evidence of clouds and disequilibrium chemistry playing a key role. While HD 189733 b is thought to host global cloud coverage, its atmospheric structure and composition remain poorly constrained due to the lack of a spectroscopic phase curve. The proposed observations will deliver a high signal-to-noise phase curve, enabling constraints on the planet’s global cloud distribution, composition, and thermal structure. MIRI’s wavelength coverage is particularly well suited to probing cooler nightside emission and identifying key molecular species such as methane and ammonia, as well as silicate cloud features. By mapping how atmospheric properties vary across the planet, these data will provide critical constraints on energy transport, cloud formation, and chemical processes in hot Jupiter atmospheres. The resulting dataset will serve as a benchmark for atmospheric models and help place HD 189733 b within the broader context of hot Jupiter diversity and formation.

Björn Benneke, Professor at the Université de Montréal and UCLA.

Program 12157: MIRI Clarity: Uncovering the Mysteries of Water Worlds and Sub-Neptunes in the Mid-Infrared
PI: Björn Benneke (UdeM/UCLA)
co-PI: Pierre-Alexis Roy (UCLA)
Time awarded: 57.6h using MIRI/LRS
Summary: Recent JWST observations have revealed a surprising diversity in the atmospheres of sub-Neptune planets, particularly near the radius valley where planets transition from gas-rich to more compact compositions. Near-infrared data suggest a progression from hydrogen-dominated atmospheres to water-rich and potentially water-dominated worlds, but overlapping molecular features and cloud effects often lead to ambiguous interpretations. This program will use JWST’s MIRI Low Resolution Spectroscopy (LRS) to observe five of the most favorable sub-Neptunes with previously detected molecular signatures. The mid-infrared wavelength range provides access to key spectral features, allowing for the direct detection of water and sulfur-bearing species that are difficult to constrain at shorter wavelengths. By combining these observations with existing data, the team aims to resolve degeneracies in atmospheric composition and better characterise the diversity of sub-Neptune atmospheres. The program will produce a uniform set of high-precision transmission spectra spanning 0.6 to 12 μm, establishing benchmark targets for understanding the most common class of planets in the Galaxy.

We also wish to congratulate IREx alumni Yayaati Chachan, Clémence Fontanive, Michael Radica, Pierre-Alexis Roy, and Jake Taylor who are all PIs or co-PIs on Cycle 5 programs. Many more JWST Cycle 5 GO programs will be supported by Canadian and IREx researchers as co-Investigators. To see all selected Cycle 5 programs, consult the STScI website. Congratulations to all astronomers with awarded time, as well as all astronomers who submitted proposals!