Universe Today
The Space Telescope Science Institute (STScI) has announced the science objectives for Webb's General Observer Programs in Cycle 4 (Cycle 4 GO) program. The Cycle 4 observations include 274 programs that establish the science program for JWST's fourth year of operations, amounting to 8,500 hours of prime observing time. This is a significant increase from Cycle 3 observations and the 5,500 hours of prime time and 1,000 hours of parallel time it entailed.
These programs are broken down into eight categories, ranging from exoplanet habitability and the earliest galaxies in the Universe to supermassive black holes, stellar evolution, and Solar System astronomy. They were selected by the Cycle 4 Telescope Allocation Committee (TAC) in February 2025, which comprised two Executive Committee Chairs, 36 Panel Chairs and Vice Chairs, 183 Discussion Panelists, 315 External Panelists, and 220 Expert Reviewers.
In terms of exoplanet studies, the observation programs for Cycle 4 focus on exoplanet characterization, formation, and dynamics. In particular, the programs address ongoing questions about exoplanet habitability and the types of stars that can host habitable planets. For instance, program GO 7068, titled "Surveying Stellar Shenanigans: Exploring M dwarf Flares for Exoplanetary Insights," focuses on the question of red dwarf stars and the hazards posed by their flare activity.
The field of exoplanets has undergone a major transition in recent years. With over 5,800 confirmed candidates (5,849 as of the writing of this article), scientists are moving from the discovery process to characterization. This consists of obtaining spectra from exoplanet atmospheres to determine what chemical signatures are present. By detecting potential biosignatures (i.e., oxygen, carbon dioxide, water, methane, etc.), scientists can measure planetary habitability more accurately.
Interestingly, the JWST was not originally designed for exoplanet characterization. However, its extreme sensitivity to infrared (IR) wavelengths and advanced spectrometers mean that Webb can obtain transit spectra from exoplanets as they pass in front of their suns. Combined with its coronographs (which block out light from a system's star), it can also detect the faint light reflected by exoplanet atmospheres and surfaces.
Red Dwarfs
In the past decade, astronomers have detected numerous rocky planets orbiting nearby M-type (red dwarf) stars. Of the 30 potentially habitable exoplanets closest to Earth, 28 orbit red dwarf stars. This is particularly good news for astronomers and astrobiologists since red dwarf stars are the most common in the Universe and account for about 75% of stars in the Milky Way. What's more, research has indicated that there may be tens of billions of potentially habitable rocky planets orbiting red dwarf stars in the Milky Way.
On the other hand, red dwarf stars are also known for being variable and prone to significant flare activity compared to Sun-like stars. Recent studies have detected several "superflares" events from red dwarfs powerful enough to remove the atmospheres of any planets orbiting them. However, recent observations by the Transiting Exoplanet Survey Satellite (TESS) have shown that red dwarf stars tend to emit superflares from their poles, thus sparing orbiting planets.
Learning more about M-type stars and their effects on planetary habitability is the purpose of GO 7068, "Surveying Stellar Shenanigans: Exploring M dwarf Flares for Exoplanetary Insights." Dhvani Doshi, a PhD student at McGill University's Trottier Institute for Research on Exoplanets, is the principal investigator of this program. Using Webb's Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument, the team will observe five active M-type stars for 5 to 10 hours each to obtain spectra as they transit in front of their stars.
They also anticipate recording 400 flare events with energies exceeding 10^{30} erg, or 6.24^42 electronvolts (ev). Per the program description:
"Through detailed analysis of flare properties and behavior in the NIR regime, our proposal aims to address critical gaps in our understanding of stellar flare phenomena on M dwarfs, refining existing models and enhancing our ability to interpret exoplanetary spectra in the presence of stellar activity."
Direct Imaging
As noted, Webb's advanced instruments also make it uniquely qualified for Direct Imaging studies. These involve observing exoplanets directly as they orbit their suns, which was previously restricted to massive planets with wide orbits. Thanks to Webb's extreme sensitivity and advanced instruments, Cycle 4 GO includes several programs that will conduct DI studies of nearby exoplanets.
This is the purpose of the GO 6915 program, titled "Direct Detection and Characterization of a Nearby Temperate Giant Planet." The Principal Investigator of this program is William Balmer, a Ph.D. candidate at Johns Hopkins University and the Space Telescope Science Institute (STScI). He and his colleagues propose directly imaging HD 22237 b using Webb's Near Infrared Camera (NIRCam) and Mid-Infrared Imager (MIRI) coronographs.
This nearby gas giant is about 37 light-years from Earth and is 5.19 Jupiter masses. As the team described in their proposal:
"These observations will constrain key atmospheric model uncertainties, like the strength of water-ice cloud opacity, the abundance of ammonia, and the strength of disequilibrium chemistry in the planet's atmosphere. This program is designed to efficiently detect the planet at high confidence, photometrically characterize the atmosphere, and refine the planet's sky-projected orbit ahead of Cycle 5; doing so will allow the community to estimate the feasibility of follow-up spectroscopy on the fastest timescale."
Another interesting program is GO 7612, "We can directly image super-Earth-sized planets near the habitable zone of Sirius B with JWST/MIRI." The PI for this program is Logan Pearce, a postdoctoral researcher from the University of Michigan. The team will conduct a direct imaging campaign using Webb's Mid-Infrared Imager and its coronagraph to search for super-earths and cold gas planets near the outer edge of Sirius B's habitable zone (HZ).
Located 8.7 light-years away, Sirius B - the companion star of Sirius A (an A-type main sequence white star) - is the closest white dwarf to the Solar System. For decades, scientists have wondered if white dwarf stars can support habitable planets. In recent years, research has indicated that planets would need to orbit closely to white dwarfs to be in their HZs. Similar to exoplanets that orbit M-type stars, rocky planets orbiting in the HZs of white dwarfs are likely to be tidally locked, with one side absorbing potentially dangerous levels of radiation.
"Our program holds the potential to detect rocky planets and cold (>70K) gas giants—a feat unlikely to be possible until the next generation of observatories comes online decades from now. If a planet-like signal is detected, follow-up proper motion measurements or spectroscopy will confirm its planetary nature and provide a detailed characterization of its physical and atmospheric properties. This program could be JWST's singular chance to directly image rocky planets in a nearby system, offering profound insights into planetary evolution around post-main sequence stars and in binary systems."
Rocky Exoplanets
In terms of exoplanet studies, Webb is also especially qualified for studying smaller, rocky planets that orbit more closely to their suns - which is where Earth-like planets are likely to reside. This presents astronomers with the exciting opportunity to examine Earth-like planets near the Solar System more closely. This includes the closest exoplanet to the Solar System, which is the purpose of the GO 7251 program, "Does Our Closest M-Dwarf Rocky Neighbor Have An Atmosphere? We Need to Find Out."
The rocky neighbor in question is LTT 1445A b, the nearest transiting rocky planet considered the most likely to have an atmosphere. The planet is a Super-Earth that orbits the primary star in a triple M-dwarf system located 22 light-years away. The planet's size (1.3 Earth radii and 2.73 Earth masses) and its equilibrium temperature (150.85 °C; 303.5 °F) are promising indications that it may have an atmosphere.
The program will follow up on recent observations made by the Hubble Space Telescope (HST) that obtained accurate measurements of the planet's size. While previous observations were made using Webb, the planet's proximity to its host star saturated most of its near-infrared observing modes. But thanks to the implementation of the NIRCam Short-Wavelength Grism Time Series, astronomers can now observe LTT1445A b without risk of saturation.
Katherine Bennett, a Ph.D. student in Planetary Sciences at Johns Hopkins University, is the program's principal investigator. Their planned observations will monitor LTT1445A b during eight transits using the NIRCam Grism Time Series template. As Bennet and her colleagues indicated in the program description:
"We note that LTT1445Ab's hotter and smaller sibling, LTT 1445Ac, is being targeted by the STScI Rocky Worlds DDT Program. By coupling the DDT emission photometry study with our NIRCam transmission spectroscopy study, we can map the presence of atmospheres within a single system. What's more, if LTT 1445Ab does not have an atmosphere, this would have profound implications for M-dwarf habitability in general."
Similarly, program GO 7875 ("The only known atmosphere on a rocky exoplanet?") will dedicate observation time to 55 Cancri e. This Super-Earth, located 41 light-years away, measures 1.875 Earth radii and has a mass 7.99 times that of Earth. Its close orbit to 55 Cancri A means it is extremely hot, with an estimated equilibrium temperature of 2000 K (1725 °C; 3140 °F). This has led astronomers to theorize that the entire planet is covered in an ocean of lava.
While not a good candidate for astrobiology studies, it is currently the only rocket exoplanet with evidence of an atmosphere. The program's principal investigator is Michael Zhang, an Inaugural E. Margaret Burbidge Prize Postdoctoral Fellow at the University of Chicago. This program will conduct MIRI MRS observations of the exoplanet during three eclipses, which will allow them to confirm the existence of an atmosphere, obtain spectra, and constrain its carbon dioxide abundance. Per the program description:
"As an old, ultra-hot (Teq=2000 K), and ultra-short-period planet, 55 Cnc e may seem a-priori like a particularly hostile place for any gaseous envelope. Understanding whether and/or how such an envelope exists on 55 Cnc e, the most observationally favorable super-Earth, has strong implications for the survivability of rocky planet atmospheres more generally."
Another exciting program is GO 7953, "Exo-Geology: Surface Spectral Features from a Rocky Exoplanet." Led by PI Kimberly Paragas, a graduate student in the Planetary Science option at the California Institute of Technology (Caltech). This program will leverage the JWST's capabilities to conduct the very first spectroscopic characterization of a rocky exoplanet's surface.
This program will observe LHS 3844 b, a Super-Earth orbiting an M-type star 49 light-years from Earth. This exoplanet is considered the most promising surface characterization target in the exoplanet census. "This will allow us to leverage the vast expertise developed for Solar System rocky bodies to establish a new field of 'exo-geology' whose goal is to explore the geological histories and mantle compositions of rocky exoplanets is to explore the geological histories and mantle compositions of rocky exoplanets," states the team in their proposal.
Planet Formation
The Cycle 4 General Observations will also use Webb's IR imaging capabilities to explore how planets form from debris disks. This will address key questions in astrobiology, not the least of which is how habitable planets evolve. To this end, program GO 6940, "Determining the Origin of Water Ice in the Beta Pictoris Debris Disk," was selected as part of Cycle Four. This campaign is led by PI Sarah Betti, an STScI postdoctoral fellow.
This program will use Webb's Near-Infrared Spectrometer (NIRSpec) and spectrograph to obtain medium-resolution spectroscopy to resolve water and carbon dioxide ices in the Beta Pictoris debris disk. Recent spectrometric observations have the presence of ices across the whole disk for the first time in a debris disk, including a hint of a significant ice population at its outer edge. These grains were not expected to survive, leading to a shift in scientists' understanding of debris disk chemistry.
This discovery also raised new questions about the role of giant collisions in producing the observed ice grains. As a result, the characterization of the origin and composition of these ices is vital to our understanding of late-stage planet formation and ice transport in disks. To this end, this program aims to conduct MIRI spectroscopy of the system's disk to resolve frozen volatiles, allowing astronomers to learn more about how planet formation occurs in debris disks.
"By mapping the whole dust clump, we can uncover the origin, chemical composition, and thermal history of the ices in this disk," per the program proposal.
These programs offer a small taste of what the JWST will study during this observation cycle. In addition to exoplanet studies, teams from around the world will use observation time to learn more about a wealth of cosmological phenomena and unresolved questions in astronomy, astrophysics, astrobiology, cosmology, and planetary geology.
Further Reading: STScI