Michael W. McElwain

With the ability to directly image Earth-like exoplanets and search their atmospheres for biosignatures, the upcoming Habitable Worlds Observatory (HWO) will also collect high signal-to-noise ratio (S/N) reflected-light photometry and spectra of nearby gas giant exoplanets. Such high-quality data would allow investigations into the formation and evolution of low-mass, low-temperature gas giants and could enable the detection of exomoons around these planets. We use the EXOSIMS direct imaging mission simulator to model HWO observations of Jupiter-radius gas giants at Earth-like and Jupiter-like instellations around the 164 stars in the ExEP target list (1.3 pc≤d≤23 pc). We find that HWO should be able to achieve S/N≥5 broadband visible-light detections of gas giants in this instellation range within 5 min of integration. At Jupiter-like instellations, 10 h of R=1000 near-IR spectroscopy with HWO should reveal water, methane, and ammonia absorption features in the atmospheres of gas giants orbiting any ExEP star, offering unique insight into the formation conditions and histories of gas giants at a wide range of semi-major axes and masses. HWO optical time-series photometry should exceed 1% flux precision for gas giants at Jupiter’s instellation level at d≤7 parsecs and for Earth-instellation gas giants around any ExEP target star. Time-series light curves at this cadence and precision could, over tens of hours, reveal rotation-induced variability comparable to Jupiter’s. Eclipses of Mars-sized exomoons may be detectable in high-cadence light curves (∼5 min exposures) of Jupiter-sized planets in the habitable zones of ExEP stars at d≤10 parsecs. For any hypothetical Earth-like exomoons with oxygen-rich atmospheres at d≤7 parsecs from the Solar System, HWO might be able to detect the spectral signature of molecular oxygen amid the parent planet’s photon noise in deep (∼400 h integration) spectroscopic HWO observations at R=1000. Such moons, if they exist, represent additional habitable worlds that HWO could investigate for biosignatures.

We report the confirmation and characterization of four transiting giant planets orbiting early M dwarfs discovered by the Searching for GEMS survey: TOI-7189 b, TOI-7265B b, TOI-7393 b, and TOI-7394B b. Joint modeling of Transiting Exoplanet Survey Satellite and ground-based photometry with precision radial velocities from the Habitable-zone Planet Finder and NEID spectrographs yields self-consistent orbital and physical parameters for all systems. The planets have short orbital periods (P = 1.25–4.17 days), masses spanning from 0.5 M_J to 2.1 M_J, and radii comparable to Jupiter (0.95 R_J < R_p < 1.02 R_J). TOI-7189 b (0.50 M_J), TOI-7265B b (0.71 M_J), and TOI-7393 b (0.61 M_J) are Saturn-like in mass and density, whereas TOI-7394B b is a dense super-Jupiter (2.10 M_J, ρ_p ≈ 2.4 g cm⁻³) on a 1.25-day orbit. All hosts are early M dwarfs with a narrow range of stellar properties, enabling a controlled comparison of giant-planet outcomes around low-mass stars. Three systems orbit super-solar-metallicity stars, while TOI-7393 ([Fe/H] = −0.35 ± 0.16) is the most metal-poor GEMS host identified to date and exhibits kinematics approaching the thin/thick-disk transition, suggestive of an older stellar population. Together, these systems reveal substantial diversity in the masses and bulk properties of short-period giant planets orbiting early M dwarfs, demonstrating that markedly different planetary outcomes can arise around stars with otherwise similar fundamental properties.

The Habitable Worlds Observatory (HWO) is the first telescope ever designed to search for life and will be a powerhouse of discovery across topics in astrophysics. The observatory was the top recommendation of the Astro2020 Decadal Survey for large missions, and a new HWO Technology Maturation Project Office was formed in August 2024 to mature the architecture, science, and technology. In this paper, we review the overall approach taken to mature the mission concept. We show progress on architecture development, integrated modeling, science cases, and technology roadmaps consistent with preformulation studies. We discuss plans for instrument studies, international engagement, and science engagement, including a Community Science and Instrument Team. Finally, we describe the plan forward to the Mission Concept Review.

Existing state-of-the-art wavefront sensing and control setups for the imaging of exoplanets utilize two high-actuator count flat deformable mirrors (DMs) to control both phase and amplitude aberrations. One of the objectives of the Exoplanet Spectroscopy (ExoSpec) project at Goddard Space Flight Center is to improve upon this regime through the development of parabolic deformable mirrors, which can address several of the key limitations in existing setups. Specifically, the need for flat DMs to be located in conjugate pupil planes drives unique packaging challenges that can be overcome by allowing the off-axis imaging elements to be controllable as well. In addition, simulations show that the use of deformable powered elements will increase the overall controllable bandwidth, up to 35% over 5 to 12λ/D. To pursue this effort, the ExoSpec group has begun testing a first-generation parabolic DM, which is already informing a second generation design. We will provide a comprehensive update on its characterization, including influence function measurements, linearity analysis, closed-loop wavefront control performance, and thermal stability assessment.

A primary goal of the Habitable Worlds Observatory (HWO) is to detect and measure the abundance of biosignature molecules, such as water (H2O) and oxygen (O2), in the atmosphere of Earth analogs. This is expected to require deep spectroscopic observations lasting hundreds of hours per planet. In this context, it is essential to optimize the spectral resolution of the spectrograph to both maximize the number of planets that can be studied over the lifetime of the mission and also to reduce the risks of false detections. The purpose of this work is to provide a framework to explore the spectral resolution design trade-space for HWO. This framework must be valid and comparable across all spectral resolutions from low (R10,000), and account for the spectral correlation of the residual starlight (i.e., speckle noise chromaticity). Leveraging the concept of “template matching,” we develop a simulation toolkit based on the Python package EXOSIMS to compute the detection significance of planets and molecules. We then simulate observations of Earth analogs around 164 stars using representative mission parameters to explore the effects of the detector noise and the correlated speckle noise floor. Our findings suggest that a moderate- or high-resolution spectrograph (R>1000) will provide higher sensitivity to critical molecules compared with a low-resolution spectroscopy mode (e.g., R∼140). The correlated speckle noise may also entirely suppress our ability to detect biosignatures at low spectral resolutions. We conclude that a more comprehensive study, combined with detailed models of its stability and other sources of correlated noise, is necessary to fully explore the trade space of spectral resolution and detectability of key species.

We present the discovery of GJ 251 c, a candidate super-Earth orbiting in the habitable zone (HZ) of its M dwarf host star. Using high-precision Habitable-zone Planet Finder and NEID RVs, in conjunction with archival RVs from the Keck I High Resolution Echelle Spectrometer, the Calar Alto High-resolution Search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrograph, and the Spectropolarimétre Infrarouge, we improve the measured parameters of the known planet, GJ 251 b ( P _b = 14.2370 days; m sin ( i ) = 3.85 − 0.33 + 0.35 M _⊕ ), and we significantly constrain the minimum mass of GJ 251 c, placing it in a plausibly terrestrial regime ( P _c = 53.647 ± 0.044 days; m sin i c = 3.84 ± 0.75 M _⊕ ). Using activity mitigation techniques that leverage chromatic information content, we perform a color-dependent analysis of the system and a detailed comparison of more than 50 models that describe the nature of the planets and stellar activity in the system. Due to GJ 251’s proximity to Earth (5.5 pc), next generation, 30 meter class telescopes will likely be able to image terrestrial planets in GJ 251’s HZ. In fact, GJ 251 c is currently the best candidate for terrestrial, HZ planet imaging in the northern sky.

The NEID Earth Twin Survey (NETS) has been delivering a rich set of precise radial velocity (RV) measurements for 41 bright, nearby main-sequence stars. Here, we describe the status of the survey after 3 yr on sky, and we present the full set of RV measurements and accompanying stellar activity indicators. We discuss intermediate survey diagnostics, including calibration of the known RV zero-point offset introduced following the Contreras fire in 2022 and the identification of an undiagnosed and previously unknown zero-point offset in 2021. An analysis of our data set using RVSearch demonstrates that for these target stars, NEID is independently sensitive to nearly all known planets with periods shorter than the NETS observing baseline. We also highlight a number of newly detected RV signals, which present exciting opportunities for future investigations.

The population of giant planets on wide orbits around low-mass M dwarf stars is poorly understood, but the unprecedented sensitivity of JWST NIRCam coronagraphic imaging now provides direct access to planets significantly less massive than Jupiter beyond 10 au around the closest, youngest M dwarfs. We present the design, observations, and results of JWST Guaranteed Time Observation Program 1184, a Cycle 1 NIRCam coronagraphic imaging survey of nine very nearby and young low-mass stars at 3–5 μm wavelengths. In the F356W and F444W filters, we achieve survey median 5σ contrasts deeper than 10⁻⁵ at a separation of 1″, corresponding to 0.20 M _Jup in F444W and 1.30 M _Jup in F356W at planet–star separations of 10 au. Our results include 3–5 μm debris disk detections and the identification of many extended and point-like sources in the final postprocessed images. In particular, we have identified a marginal point-source candidate having flux and color limits consistent with model predictions for a young sub-Jupiter-mass exoplanet. Under the assumption that the candidate is not confirmed, we place the first direct-imaging occurrence constraints on M dwarf wide-orbit (semimajor axes of 10–100 au), sub-Jupiter-mass exoplanets (0.3–1 M _Jup). We find frequency limits of σ and 3σ confidence, respectively. This survey showcases the unprecedented capabilities of JWST NIRCam coronagraphic imaging when targeting young, low-mass stars and acts as a precursor to broader surveys to place deep statistical constraints on wide-orbit, sub-Jupiter-mass planets around M dwarfs.