About this Article

STScI completed the proposal review and telescope allocation process for JWST Cycle 4 GO/AR, scheduled to begin July 1, 2025. During its fourth year of science operations, JWST will continue to enable groundbreaking work across all areas of astrophysics, from small bodies and giant planets in the solar system, to exoplanets and planetary systems young and old; from the birth and death of very low mass stars, to the most massive; to the study of galaxies throughout cosmic time, and the earliest and most distant stars. Cycle 4 will encompass approximately 8,500 hours of prime observations, during which JWST will continue to push the frontier of our knowledge further into the unknown. The Cycle 4 Science Program is the result of an unprecedented brainstorm by the worldwide astronomical community that submitted 2,377 proposals, setting a new record for proposals received in response to any Call for Proposals by a major observatory. 

Proposal Submission

The GO Cycle 4 Call for Proposals was released August 1, 2024 with a deadline of October 16, 2024. An extra week was provided for investigators who were facing extenuating and unforeseen circumstances beyond their control, such as the impact of Hurricane Helene. The total time request of the submitted 2,377 proposals was 75,138 hours (for 8,500 hours available in Cycle 4), corresponding to an over-subscription of around 9:1. All proposals were verified for completion.  A total of 106 proposals (primarily identified by reviewers) were investigated for compliance during the review. Regarding dual anonymous violations, 50 proposals were flagged of which 12 were disqualified, 22 were issued warnings and 16 were determined to not be violations. Regarding page limit or proposal format violations, 36 proposals were flagged of which 14 were disqualified, 17 were issued warnings, and 5 were determined to not be violations. 20 proposals were flagged for various other violations of which 4 were disqualified, 3 were issued warnings, and 13 were determined to not be violations. The 30 recommendations for disqualification were brought to the Director’s Office for approval. One additional proposal was withdrawn by the PI.

The 2,346 compliant proposals included: 2,082 GO proposals, 10 Pure Parallels proposals, 50 Survey proposals, 106 Regular Archival Research proposals, 20 Archival Legacy proposals, 88 Theory proposals, 9 Calibration proposals, 4 Cloud Computing proposals, and 15 Data Science Software proposals (some proposals are in multiple categories). They were submitted by a worldwide community of 6,730 unique investigators from 61 countries and 46 states from the United States (plus Washington, DC and Puerto Rico).

Adjustments to Proposals Selection Planning

In anticipation of a large number of proposal submissions, and to achieve a more balanced workload and sharing of responsibilities, STScI recruited the largest Telescope Allocation Committee (TAC) it has ever assembled, consisting of 2 Executive Committee (EC) Chairs, 36 Panel Chairs and Vice Chairs, 183 Discussion Panelists (Galactic TAC Discussion Panelists and Extragalactic TAC Discussion Panelists), 315 External Panelists (Galactic TAC External Panelists and Extragalactic TAC External Panelists), and 220 Expert Reviewers. The TAC members were well-distributed geographically and drawn from a wide range of institution types.

Adjustments were made to the Cycle 4 process following the JWST Users Committee (JSTUC) recommendations. GO proposal size boundaries were changed to achieve a more balanced workload and responsibility in telescope allocation for the External and Discussion panelists and the Executive Committee (EC), and to accommodate the growing complexity of JWST programs. GO Proposals were classified as Very Small (≤ 20 hours), Small (> 20 and ≤ 50 hours), Medium (> 50 and ≤ 130 hours) and Large (> 130 hours). Very Small GO proposals and Regular AR proposals were sent for review to the External panels. Small and Medium GO proposals and all Target of Opportunity and Survey proposals, regardless of size, were sent for review to the Discussion panels. The Discussion panels also advised the Panel Chair and Vice Chair on the scientific merit of a subset of the Large/Treasury proposals within their science area.  To decrease the EC workload and improve the match of proposal keywords and reviewer’s expertise, the Cycle 4 EC was split into two parts: Galactic and Extragalactic. The two ECs were in charge of reviewing Large GO proposals, Treasury GO proposals, Legacy AR proposals and other requests for substantial resources, such as Pure Parallel proposals. The two ECs also had the input from Expert Reviewers that provided reviews asynchronously.

The JSTUC strongly endorsed: (1) the reduction of the page limits to decrease reviewer workload and to align with other large NASA and community-wide facilities; and (2) the update and diversification of scientific keywords and scientific categories, to better match JWST science topic distributions, and to achieve better proposal distribution across panels. The updated scientific categories are the following:

• Solar System Astronomy
• Exoplanet Atmospheres and Habitability
• Exoplanet System Formation and Dynamics
• Stars and Stellar Populations
• Gas, Dust and the ISM
• Nearby Galaxies to Cosmic Noon
• High-Redshift Galaxies and the Distant Universe
• Super-Massive Black Holes and Active Galaxies

Approximately 250 proposals were re-assigned to a different scientific category than that originally identified by the proposers, ensuring the best matches between proposal keywords and reviewers’ expertise. The proposals were assigned for review taking into account reviewers’ expertise, conflicts of interests, and aiming for a balance workload.

Review Process

All documents and orientation material related to the review process are publicly available on JDox. The proposals sent to the External panels were reviewed asynchronously. After the final reviews and grades were submitted, these proposals were ranked and the top ranked proposals were recommended for approval. For the proposals sent to the Discussion and EC panels, the preliminary grades were used to triage proposals and to create a reading list of proposals selected for discussion by the panels.

The Discussion panels were constituted by 18 topical panels that met virtually for four days during the week of February 3, 2025. The two EC panels (Galactic and Extragalactic) met in person at STScI the following week. During this phase, Discussion and EC panels:

• Discussed proposals in turn and entered numerical scores as grades after each discussion.
• Assessed the final ranking of proposals for science balance, addressing science duplications within the panel (intra-panel).
• Reviewed team expertise for top ranked proposals.
• Wrote proposals feedback comments (signed-off by the respective panel Chair).
• Provided feedback to their Chairs and Vice Chairs on a subset of Large, Treasury, Legacy, and Pure Parallel proposals to help in the ECs deliberations.

Finally, the Chairs reviewed the list of top-ranked proposals recommended by the External panel in the same scientific category to assess the overall topical balance.

Duplication Checking and Adjudications during the TAC Meeting

As mentioned above, when assessing the science balance of the top-ranked proposals in their panel, the panelists are asked to identify science duplications. Science duplications can take a number of different forms, but are generally considered duplications when the scientific outcomes of different programs are very similar, and could overlap or be redundant. For example, if two programs wish to do the same science with the same target, even if the observations requested are not direct duplications, or if two programs propose to do the same science on different but very similar targets. There is no policy prohibiting science duplications, but in some cases the TAC may consider them an inefficient use of JWST time, leading to the rejection of one of the proposals. Science duplications among recommended proposals in a same panel (intra-panel) were addressed during the ranking process, while science publications among recommended proposals in different panels (cross-panel), including the External panels, were addressed by the corresponding panel Chairs and Vice Chairs during the Chairs tag-ups.

In addition, Panel Chairs and Vice Chairs adjudicated observation duplications among Cycle 4 recommended proposals. Observation duplications are observations of the same target or field using the same instrument, same mode, same optical elements and with an exposure time within about a factor of four. The primary goal of the JWST Duplicate Observations Policy is to maximize telescope efficiency by eliminating unnecessary observations. In general, observation duplications are only allowed if there is a clear scientific justification. Exceptions include partial duplications, impacting a subset of the observing program and where removing the observation from one or other program could harm the science. If there are no mitigating circumstances, one observation/visit/target will be disallowed. Previous cycle observations have priority. 

Intra-cycle observation duplications are adjudicated on a case-by-case basis following the TAC recommendations. To do this, prior to the review, all proposals were loaded into a database to run the intra-cycle observation duplication checking (this is a stand-alone process designed only to assist the proposal selection, and is separate from the duplication checking that happens after the proposals are accepted and the proposals become JWST programs). Once ranked lists were finalized, the proposals that were being recommended were flagged for observation duplications. Panel Chairs and Vice Chairs were asked to assist and analyze any identified instances with cross-panel issues; intra-panel were handled via the ranked list with concurrence by the Chairs. Ten instances were found for observation duplications that needed to be adjudicated during the TAC meeting. Panel Chairs and Vice Chairs recommended disallowing one or the other set of observations of a specific target or targets. Those recommendations were accepted for implementation and appropriate comments were applied.

Note that after the proposals are accepted and the Cycle 4 observations are ingested, they all undergo verification and duplication checking against observations in previous cycles and in Cycle 4. As indicated above, when an observation duplication is found, it is not rejected automatically. It is flagged for further review because there can be valid reasons for repeating observations of individual targets, and repeat observations that are justified scientifically are approved for execution.

Telescope Allocation

The most important outcome of the TAC meetings are the ranked lists because telescope allocation is completed by stepping down those rankings. Each panel was provided an initial hour allocation based on the GO hours submitted to that panel (referred to 1N), and they were asked to carefully rank top proposals to twice that hour allocation (2N). Proposals of all types above the initial hour allocation (1N) were recommended, and the Chair provided guidance on the panel preferences regarding allocation below 1N. Telescope allocation was completed by stepping down the rankings provided by the panels, taking into account the overall science balance, the panel preferences, and the Chairs adjudications of observation duplications.  

A heartfelt thank you to all our reviewers that showed an extraordinary commitment to the successful completion of the selection process. The JWST TAC would not be possible without their critical support and contributions.

Cycle 4 Science Program

The STScI Director is the Selecting Official for JWST. The recommendations from the Cycle 4 TAC were presented to the STScI Director for endorsement on February 28, 2025. The results were announced to the community on March 11, 2025. Table 1 summarizes the main results. The Science Program is comprised of 274 proposals, with an acceptance rate of 1 in 8.6 for proposals and 1 in 8.7 for hours. For Very Small  proposals 112 were accepted for 1,338 hours, Small 86 for 3,014  hours, Medium 38 for 2,701 hours, and Large 8 for 1,524 hours. Figure 1 shows the size distribution of accepted proposals as a percentage of the total prime time of the Science Programs for Cycles 1 to 4. The Science Program includes 1 ToO with an activation less than 14 days (Disruptive), 13 ToO with an activation > than 14 days (non-Disruptive), 4 for Joint JWST-ALMA proposals (for 50.5 ALMA hours), 1 Joint JWST-HST (for 16 orbits), and 1 Joint JWST-NASA Keck (2 nights). Overall, 2,196  hours of Cycle 4 GO proposals (24.6%) have zero Exclusive Access Period.

The accepted proposals include representation from all major instrument observing modes (Table 2). The distribution of time in the different instruments for accepted proposals is: MIRI 32.5%, NIRCam 20.3%, NIRISS 7.1%, NIRSpec 40.2%, Imaging 23.5% and Spectroscopy 76.5%. The accepted proposals span the full range of science anticipated for JWST. Figure 2 shows the distribution by scientific category as a percentage of the total prime time of the Cycle 4 Science Program: 19.1% of prime hours correspond to accepted proposals in Exoplanet Atmospheres and Habitability, 9.5% to Exoplanet System Formation and Dynamics, 5.9% to Solar System; 13.3% to Stars and Stellar Populations,  8.3% to Gas, Dust and the ISM, 9.6% to Nearby Galaxies to Cosmic Noon, 24.9% to High-Redshift Galaxies and the Distant Universe, and 9.3% to Super-Massive Black Holes and Active Galaxies.

A full summary of the acceptance statistics is posted on the JSTUC webpage (Cycle 4 GO/AR Results). Information about the approved programs is now available in the Cycle 4 GO page. 

The Large, Treasury, and Archival Legacy programs selected by the Galactic Executive Committee were: 

• “SuperDisks: A high-fidelity public database of protoplanetary and debris disk MIRI-MRS spectra” (AR), aiming to exploit MRS archival observations to improve our understanding of inner protoplanetary disk composition and its connection with planet formation. 
• “Charting the Cosmic Shoreline” (245 hours), with the goal of finding high mean molecular weight atmospheres in six temperate exoplanets around M-dwarf harboring multiple-planet systems to understand where atmospheres are retained.
• “The Cold Worlds Spectral Library” (175 hours), with the goal of creating a high signal-to-noise library of cold brown dwarf spectra (2.8-20 microns) to help develop atmosphere models.
• “Exploring the magnetic environments of Uranus and Neptune with JWST” (139 hours), aiming to capture the changing auroral and ionospheric conditions over a full solar rotation (at a period when solar activity is peaking), providing an archetype for exoplanets magnetospheres.
• “The supremely deep trans-Neptunian object survey: A critical test of planet formation models” (135 hours),  with the goal of extending the known size distribution of the cold classical TNO population down to 1 km.
• “Mining JWST data for hidden asteroid gems” (Archival), with the goal of achieving a 10-fold increase in the identified sample of small asteroids, key to planetary-defense efforts, to the study of meteorite sources and to the study of the dynamical evolution of the asteroid belt.

The Large, Treasury, and Archival Legacy programs selected by the Extragalactic Executive Committee were: 

• “MINERVA: Unlocking the Hidden Gems of the Distant Universe and Completing HST and JWST’s Imaging Legacy with Medium Bands” (260 hours), observing in the well-studied HST/JWST extragalactic survey fields of PRIMER-UDS, PRIMER-COSMOS, CEERS/AEGIS, and JADES-GOODS-N.
• “Unlocking the nature of the first galaxies with ultra-deep rest-UV spectroscopy” (200 hours), by observing 154 galaxies at z > 5, this program aims to understand what powers galaxies' ionizing spectra; to reveal direct emission from very massive stars; to understand early star formation and black hole growth; and to constrain the onset of reionization.
• “The CLASSYIR Treasury: Unveiling the Cosmic Engines Powering Galaxies with JWST/MIRI” (79 hours), by observing 31 local star forming galaxies, together with existing datasets, this program aims to provide templates to understand the shape of the full ionizing spectra of the sources powering nebular emission across cosmic time.
• “J-Virgo:  A JWST Treasury Survey of the Virgo Cluster” (147 hours), a program that will use precise distances estimated with the TRGB method to create the first 3D map of a cluster within the virial radius, helping to understand the impact of cluster environment on galaxy evolution, and to anchor a Surface Brightness Fluctuations distance scale.
• “Vast Exploration for Nascent, Unexplored Sources” (VENUS) (243 hours), that by observing 60 well-studied massive clusters will search for apparently bright but intrinsically faint distant objects with the goals to identify star clusters and individual stars, to characterize the low-end of the black hole mass function, and to search for supernovae at z=1-8.

An Increasingly Broad JWST Community

The 274 accepted proposals have 2,173 unique investigators at institutions world-wide from 39 countries, 41 US states plus Washington, DC, 6 Canadian provinces and territories, and 21 ESA countries, plus 3 ESA-cooperating countries. 702 proposals were led by PIs from ESA countries (30% of proposals, 25.7% of total prime time in the Science Program), 78 from CSA (3.3% of proposals, for 9.6% of total time time). The statistics indicate a continued success at reaching an increasingly broad community, with a remarkable 41% of PIs being first time HST or JWST PIs (104 of 252 unique investigators).

What’s Next for Cycle 4 Accepted Proposals

All JWST observing proposals recommended by the TAC are subject to technical review before they are accepted for execution and become JWST programs. The technical review may identify changes to the implementation in order to optimize the observations. Recommended proposals are also checked for observation duplications against observations in previous cycles. Cycle 4 verification and duplication checking have already started. Cycle 4 will start July 1, 2025 and end June 30, 2026, but some Cycle 4 observations will be scheduled beyond Cycle 4 boundaries because of visibility windows and to maximize JWST observing efficiency. Likewise, about 10% of the time available between July 1, 2025 and June 30, 2026 (corresponding to the start and end dates of Cycle 4) will be used to execute observations from previous cycles.

Cycle 4 will initiate a formula-based system for setting grant allocations. STScI hosted two JWST Cycle 4 Grants Webinars on April 2, 2025 and April 8, 2025 to support the community with grant preparation prior to the budget deadline on May 8, 2025. All submitted budgets will be subject to review of allowability, scope and reasonableness by the Financial Review Committee, composed of members of the community, and STScI.  

Cycle 5 Timeline

The high oversubscription rate implies that there were unfortunately many excellent proposals well-liked by the reviewers that could not be selected in Cycle 4. But another opportunity will soon open. The JWST Cycle 5 Call for Proposals is scheduled to be released on August 1, 2025 with a deadline of Wednesday October 15, 2025.

 Get Involved

The JWST peer review processes is one of the most important community activities STScI undertakes during the year. Given the unpreceded response to the JWST Cycle 3 and 4 Call for Proposals, STScI will need to continue to recruit an increasing number of community members to serve as reviewers in future Cycles. If you are interested in serving, please volunteer. Typically, postdocs with at least two years of experience, and those more senior are eligible, but in exceptional cases, more junior researchers could be considered. Most reviewers reflect that, in spite of the time demand, serving as a reviewer is a rewarding activity. As described above, multiple adjustments were made to the Cycle 4 proposal review process to decrease the workload on the reviewer and these changes were positively received. STScI cannot run the proposals selection without the expertise and support of many community members, and highly values the time and energy they commit year after year to making these reviews a success.

Another way to get involved is to contact the JWST Users Committee (JSTUC). The JSTUC is responsible for advising STScI and the JWST Project on all aspects of observatory operations. This provides a practical way of ensuring that the observatory operations proceed in a coordinated manner in order to maximize its scientific performance.

You can also volunteer to serve on the JSTUC. Members are drawn from the U.S, ESA and CSA communities, and membership lasts for three years. The committee meets twice a year, typically in the Spring and in the Fall, with additional communications as warranted. Several members rotate off after every meeting, approximately every 6 months, so we are always in search of new JSTUC members. Self-nomination is very welcome. Submissions are encouraged to include a short cover letter summarizing the nominee’s relevant background and JWST-related interests and a curriculum vitae, and should be submitted to jstuc-nominations@stsci.edu. Nominations will be considered on a rolling basis.

Acknowledgements

STScI is extremely grateful to everyone that was involved in any of the many stages and tasks related to the proposal selection process. Every cycle we received numerous verbal comments and e-mails from reviewers and NASA officials who greatly appreciated the professionalism and help shown by all reviewers and STScI staff. 

We thank all JWST Cycle 4 reviewers, namely the 2 Executive Committee Chairs, 36 Panel Chairs and Vice Chairs, 183 Discussion Panelists, 315 External Panelists, and 220 Expert Reviewers. Thanks to their generous support, expertise, and commitment, STScI was able to continue implementing a careful peer-review selection process in spite of the unpreceded high number of proposal submissions. Their contribution plays an important role at maximizing the science return of the mission.

In addition, numerous STScI personnel supported the review at its different stages. The overall coordination was led by the TAC Managers Katey Alatalo and Amaya Moro-Martín, with extensive support from Technical Managers Aleksandra Hamanowicz, Brett Blacker, and Amber Armstrong who devised and coordinated the TAC logistics and technical aspects.  A heartfelt thank you to Brett Blacker for coming back from retirement to support the JWST Cycle 4 proposal selection. Meeting logistics were led by Sherita Hanna in the Events Planning Group.

Among the others involved in making the process a success were:

• Director’s Office: Nancy Levenson, Mercedes López-Morales, Jennifer Lotz, Neill Reid
• Event Support (EPG and ESA): Melody Easton, Sherita Hanna, Marleen Palacios Calderon, Victory Ramnarine, Jean-Baptiste Regnard (ESA), Shemiah Smith-Ramos, Darlene Spencer
• Instruments & Telescope Support: Marta Boyer, Alicia Canipe, Dave Golimowski, Diane Karakla, Sarah Kendrew, Stephanie LaMassa, Katie Murray, Alberto Noriega Crespo, Patrick Ogle, Brian O’Sullivan, Deepashri Thatte, Kevin Volk
• Observers (JWST Mission Office): Stacey Bright, Tom Brown, Macarena Garcia-Marin, Jeff Valenti
• Observers (CSA): Jean Dupuis
• Observers (ESA): Chris Evans, Paule Sonnentrucker
• Observers (NASA): Mic Bagley, Knicole Colon, Hannah Jang-Condell, Michael McElwain, Stefanie Millan, Jane Rigby, Amber Straughn
• OPO: John Godfrey, Pam Jeffries
• Panel Support Staff: Gagandeep Anand, Amber Armstrong, Tri Astraatmadja, David Coulter, Alejandro Crespo Gómez, Milo Docher, Ivanna Escala, Chamani Gunasekera, Aiden Kovacs, Logan Jones, Mariarosa Marinelli, Daniel Maschmann, Shelly Meyett , Blair Porterfield, Adarsh Ranjan, Christian Soto, Giovanni Strampelli, Ryan Rickards Vaught, Alison Vick, Weston Eck, Brian York
• Scheduling: Beth Perriello, Tony Roman
• Science Mission Office: Katey Alatalo, Amber Armstrong, Brett Blacker, Andy Fruchter, Aleksandra Hamanowicz, Amy Jones, Susan Kassin, Claus Leitherer, Rebecca Levy, Joshua Lothringer, Crystal Mannfolk, Amaya Moro-Martín, Nikolay Nikolov, Jamila Pegues, Marc Postman, Dave Stark, Linda Smith, Laura Watkins
• Tech Support: Gary Gilbert, Kevin Flinn, Rob Gontrun and the ITSD team.
• WASABI Support:  Jeff Bucklew, Aasif Chanandin, Alex Framerini, Craig Hollinshead, Lauretta Nagel, Doug Paul
• Facilities: Raven Baxter, Brad Bukowsky, Andre DeShazo, Bermond Few, Rob Franklin, Tiffany Lallo, Trevor Thompson, Richard Washington, Mike Venturella, Gee Williams.
• Housekeeping/Custodial Staff: Carrie Harris, William White.
• Catering: Carma’s Catering and Alma Cocina Latina

Thank you!

 
CSA & ESA Hours/Proposals is GO/Survey only; +18.6 Hours are from Calibration Pool

Imaging 23.5% and Spectroscopy 76.5%.