HWO projects may support: a) new "precursor" science observations that help to close mission architecture trades; and b) projects that mature HWO technologies and/or algorithms using Keck's 10-meter segmented telescopes as a testbed. Like other proposals for NASA-Keck time, HWO Sci-Tech proposals will be reviewed using a DAPR process. Science proposal topics may address any facet of the mission architecture and are not limited to high-contrast or exoplanet-related observations.
HWO programs are allocated a maximum of seven nights of combined Keck I and II time per semester. NASA solicited HWO proposals in 2025B.
The PI, title, abstract, and semesters in which time was awarded for the successful HWO proposals are listed below.
Time awarded in semesters 2025B, 2026A
The Habitable Worlds Observatory (HWO) will be NASA's next flagship space telescope to search for biosignatures on terrestrial worlds in the habitable zones of nearby Sun-like stars. The exact telescope architecture will depend on the core science requirements of the mission, which in turn reflect how many Sun-like stars with the right characteristics are available to survey in the solar neighborhood. A list of the most promising stars has been released to the community to carry out precursor science and target vetting. About one-third of these have significant astrometric accelerations between Hipparcos and Gaia, which may be caused by previously unknown giant planets, brown dwarfs, or stellar companions--all of potential concern for a campaign with HWO if they influence the orbital stability of habitable-zone terrestrial planets. We propose a Keck/NIRC2 high-contrast imaging survey to determine the nature of companions in these systems, with a focus on the subset of stars exhibiting long-term, low-amplitude accelerations. We will (1) identify the nature of companions accelerating FGK targets by probing their outer regions, (2) refine the orbits of known binaries, and (3) uniformly search for close-in stellar companions for 78% of the total 164-star HWO target list visible from Keck. Non-detections with deep ground-based imaging will be especially favorable to target with more sensitive coronagraphic observations using the James Webb Space Telescope to characterize the orbits and atmospheres of cold brown dwarfs and giant planets in these systems. In addition to establishing the best targets for finding nearby habitable-zone planets, results from this program will have important implications for the primary mirror size, inner working angle, and mission goals of HWO.
Time awarded in semester 2025B
Exoplanet direct imaging allows us to directly probe and characterize the exoplanet's atmosphere, potentially enabling biosignature detection. A key barrier to reaching the 10^-10 contrast levels required to directly image an Earth-analog with the Habitable Worlds Observatory (HWO) is maintaining wavefront stability on the order of tens of picometers, in particular in the presence of a segmented primary mirror. Keck Observatory is the only facility with all of the hardware components necessary for validating HWO segment phasing strategies: a large segmented primary mirror, capacitive edge sensors, deformable mirror, Zernike wavefront sensor (ZWFS), and high contrast science instruments. We propose to use Keck as an HWO testbed for developing and validating wavefront sensing and control loop strategies, demonstrating the full system-level segment control architecture for HWO using existing infrastructure.
Time awarded in semesters 2025B, 2026A, 2026B, 2027A
To discover rocky planets in the habitable zones of the nearest sun-like stars, and measure their masses, the exoplanet astronomy community must characterize and improve the long-term RV stability of the Extreme Precision Radial Velocity (EPRV) spectrographs on the largest-aperture telescopes. Rocky planets in habitable zones of sun-like stars produce RV signals smaller than 1 m/s with orbital periods of ~1 year. Thus, we need not only an RV precision better than 1 m/s, but also the assurance that the RV calibration is stable on timescales of several years. The Keck Planet Finder (KPF) is a recently commissioned EPRV spectrograph, with demonstrated precision of 30 cm/s on timescales of a single night to several weeks. However, the RV precision of the facility has not yet been demonstrated on timescales of >1 year. The KPF predecessor, HIRES, had a demonstrated stability of ~2 m/s over a 30 year baseline, and observed many of the candidate HWO target stars. However, HIRES is no longer being used routinely by the EPRV community; the most recent HIRES observations of many HWO targets were several years ago. If we allow large gaps in time to accumulate between HIRES and KPF observations, we will not be able to take full advantage of decades of previous investments with the Keck Observatory, and we will inhibit the detection of long-period planets. While a subset of the HWO targets have been observed on KPF in the intervening time, the long-term stability of KPF has not yet been demonstrated for these targets, let alone for the 67 other nearby bright FGK type stars of interest for HWO that are accessible from Keck. Further development of the Data Reduction Pipeline is a crucial step in reducing these errors. To give KPF the best possible chance of finding exo-Earths and/or setting mass upper limits for HWO targets, we need to (1) increase our sample size (at least at low cadence) to all RV-viable HWO targets, and (2) obtain 5 semesters of nearly contemporaneous RVs of these well-studied stars with KPF and HIRES, thereby bolting together the RV calibrations of the two instruments and maximizing the time baseline of useful observations. These results will be vital for figuring out which HWO candidate target stars are suitable for intensive EPRV monitoring, and help to forecast realistic detection limits that will result from future campaigns. We will obtain msini upper limits for the 67 HWO stars we study. We will ensure the long-term RV baselines of these stars from the HIRES to KPF eras, allowing the characterization of planetary systems architectures both at and beyond the habitable zones of these stars. Our program has the potential to contribute to the discovery of exo-Earths of HWO targets, although many additional RVs beyond what we request here are likely needed to accomplish the last task.
(last updated February 23rd, 2026 15:25:22)
The NASA Exoplanet Science Institute is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.
