NASA Exoplanet Science Institute

Abstract Clouds are the largest source of uncertainty in climate simulations. For exoplanets, cloud simulation is particularly challenging because of the lack of observational data to tune parameterized cloud models. Here we apply Community Aerosol and Radiation Model for Atmospheres ( CARMA ), a size-resolved bin cloud microphysics model, to the atmospheric global climate model Community Atmosphere Model (CAM6) and simulate exoplanets with a range of planetary rotation rates. CARMA produces fewer liquid clouds than the native CAM6 parameterized cloud microphysics scheme (Morrison–Gettelman two-moment microphysics, MG), more ice clouds, and a significantly different ice cloud size distribution. Overall, this leads to a decrease in the magnitude of the net CRE by 4–10 W m −2 , which is unlikely to change the determination of habitability from a climate perspective in most cases. The difference in ice cloud size distribution is likely to strongly affect transmission spectral retrievals. Our work confirms that the MG parameterized cloud microphysics scheme can produce reasonable climate simulation when extrapolated to some exoplanet contexts and highlights the value of resolved cloud microphysics for evaluating parameterized schemes and for interpreting observations.

Abstract As the diversity of exoplanets continues to grow, it is important to revisit assumptions about habitability and classical HZ definitions. In this work, we introduce an expanded ’temperate’ zone, defined by instellation fluxes between 0.1 < S/S⊕ < 5, thus encompassing a broader range of potentially habitable worlds. We also introduce the TEMPOS survey, which aims to produce a catalogue of precise radii for temperate planets orbiting M dwarfs with Teff ≤ 3400 K. This work reports the discovery and characterisation of two planets in this temperate regime orbiting mid-type M dwarfs: TOI-6716 b, a Rb = 0.98 ± 0.07 R⊕ planet orbiting its M4 host star (R⋆ = 0.231 ± 0.015R ⊙, M⋆ = 0.223 ± 0.011 M ⊙, Teff = 3110 ± 80 K) with a period $P=4.7185898^{+0.0000054}_{-0.0000041}\, \mathrm{d}$ , and TOI-7384 b, a Rb = 3.56 ± 0.21 R⊕ planet orbiting an M4 (R⋆ = 0.319 ± 0.018R ⊙, M⋆ = 0.318 ± 0.016 M ⊙, Teff = 3185 ± 75 K) star every $P=6.2340258^{+0.0000034}_{-0.0000036}\, \mathrm{d}$ . The radii of TOI-6716 b and TOI-7384 b have precisions of 6.8 % and 5.9 % respectively. We validate these planets with multi-band ground-based photometric observations, high-resolution imaging and statistical analyses. We find these planets to have instellation fluxes close to the inner (hotter) edge of the temperate zone, with Sb = 4.4 ± 1.1 S⊕ and Sb = 4.9 ± 1.1 S⊕ for TOI-6716 b and TOI-7384 b respectively. Also, with a predicted TSM similar to the TRAPPIST-1 planets, TOI-6716 b is likely to be a good rocky-world JWST target, should it have retained its atmosphere.

Context . Ganymede is the only moon in the Solar System with an intrinsic magnetic field that actively interacts with the Jupiter magnetosphere. This precipitates energetic electrons that generate ultraviolet (UV) auroral emission. Aims . In sunlit auroral regions, the observed emission partly overlaps with the solar continuum reflected by the surface. An accurate modeling of the observed UV spectra therefore requires precise knowledge of the surface spectral reflectance. Methods . We analyzed Juno/UVS data acquired during the 34th perijove (PJ) flyby to constrain the Ganymede surface reflectance in the 140−205 nm range. We used the non-local thermal equilibrium radiative transfer model originally developed to simulate the auroral emission of Ganymede, which also accounts for the reflection of solar flux by the satellite surface, to fit the observed spectra in sunlit auroral regions. Results . Our results revealed that the reflectance varies strongly spatially and spectrally from 0.1% to 8% in the [140 nm; 205 nm] wavelength range. This indicates a significant surface heterogeneity. This variability likely reflects long-term interactions between the icy surface of Ganymede and precipitating energetic particles, which alter the ice structure and crystallinity and its chemical composition. In addition, the derived reflectance maps show no clear correlation with the visible surface features of Ganymede, suggesting that the UV reflectance is primarily shaped by irradiation-driven processes and not by the geological morphology. Conclusions . The resulting reflectance maps provide a critical input for future UV auroral emission modeling, particularly in preparation for observations by the Juice/UVS mission.

Context . Super-Earths and mini-Neptunes are missing from our Solar System, yet they appear to be the most abundant planetary types in our Galaxy. A detailed characterization of key planets within this population is important for understanding the formation mechanisms of rocky and gas giant planets and the diversity of planetary interior structures. Aims . In 2019, NASA’s TESS satellite found a transiting planet candidate in a 17.6-day orbit around the star TOI-283. We started radial velocity (RV) follow-up observations with ESPRESSO to obtain a mass measurement. Mass and radius are measurements critical for planetary classification and internal composition modeling. Methods . We used ESPRESSO spectra to derive the stellar parameters of the planet candidate host star TOI-283. We then performed a joint analysis of the photometric and RV data of this star, using Gaussian processes to model the systematic noise present in both datasets. Results . We find that the host is a bright K-type star ( d = 82.4 pc, T eff = 5213 ± 70 K, V = 10.4 mag) with a mass and radius of M ⋆ = 0.80 ± 0.01 M ⊙ and R ⋆ = 0.85 ± 0.03 R ⊙ . The planet has an orbital period of P = 17.617 days, a size of R p = 2.34 ± 0.09 R ⊕ , and a mass of M p = 6.54 ± 2.04 M ⊕ . With an equilibrium temperature of ~600 K and a bulk density of ρ p = 2.81 ± 0.93 g cm −3 , this planet is positioned in the mass-radius diagram where planetary models predict H 2 O- and H/He-rich envelopes. The ESPRESSO RV data also reveal a long-term trend that is probably related to the star’s activity cycle. Further RV observations are required to confirm whether this signal originates from stellar activity or another planetary body in the system.

Abstract The HWO Target Stars and Systems 2025 (TSS25) list is a community-developed catalog of potential stellar targets for the Habitable Worlds Observatory (HWO) in its survey to directly image Earth-sized planets in the habitable zone. The TSS25 list categorizes potential HWO targets into priority tiers based on their likelihood to be surveyed and the necessity of obtaining observations of their stellar properties prior to the launch of the mission. This target list builds upon previous efforts to identify direct imaging targets and incorporates the results of multiple yield calculations assessing the science return of current design concepts for HWO. The TSS25 list identifies a sample of target stars that have a high probability to be observed by HWO (Tiers 1 and 2), independent of assumptions about the mission’s final architecture. These stars should be the focus of community precursor science efforts in order to mitigate risks and maximize the science output of HWO. This target list is publicly available and is a living catalog that will be continually updated leading up to the mission.

Abstract Betelgeuse—the closest M-supergiant to the Sun—has recently been predicted to host a lower-mass stellar companion that orbits the primary with a period of ∼6 yr. The putative stellar companion is thought to cause the long photometric modulation observed in Betelgeuse, which cannot be explained by stellar pulsations. Additionally, radial velocity and astrometric data also point to a stellar companion. Here we present diffraction-limited optical speckle imaging observations obtained on the 8.1 m Gemini North telescope in 2020 and 2024. The 2020 observations were taken during the Great Dimming event and at a time when the stellar companion was predicted to be unobservable because it was directly in line with Betelgeuse itself. The 2024 observations were taken 3 days after the predicted time of greatest elongation for the companion. A comparison of the 2020 and 2024 data reveals no companion in 2020 (as expected) and the probable detection of a companion in 2024. The presumed stellar companion has an angular separation and position angle of 52 mas and 115° east of north, respectively, which is in excellent agreement with predictions from dynamical considerations. The detected companion is roughly 6 magnitudes fainter than Betelgeuse at 466 nm. While this is only a 1.5σ detection, five results are in reasonable agreement with the predictions: the appearance of the companion at quadrature; the angular separation from Betelgeuse; the position angle with respect to Betelgeuse; the magnitude difference; and the estimated mass of the companion.

Direct characterization of potentially habitable terrestrial exoplanets around Sun-like stars requires extremely precise instrumentation capable of measuring a planet-star contrast ratio of 10-10. This instrumentation challenge pushes the limits of optical technology, with state-of-the-art coronagraphs requiring extremely precise wavefront control and large, complex, and expensive instrument designs. These bulk optics coronagraph instruments typically have limited measurable optical bandwidths and high sensitivity to the overall telescope pupil design (i.e. on-axis vs off-axis telescope configurations) and high sensitivity to optical aberrations. The AstroPIC project is applying programmable integrated photonics to develop a new kind of coronagraph instrument that is capable of reaching the theoretical limits of optimal coronagraph performance. This will result in a coronagraph instrument that is orders of magnitude smaller, less massive, and more flexible compared to traditional bulk optics designs, with the goal of increasing the Exo-Earth science yield of NASA’s Habitable Worlds Observatory flagship mission. The AstroPIC project is leveraging commercial silicon photonics fabrication to develop a coronagraph instrument that couples light from a telescope pupil plane into a mesh of integrated Mach-Zehnder interferometers on a photonic integrated circuit (PIC). The coupling is achieved by using a lenslet array to sample and focus the telescope pupil into an array of grating coupler waveguide inputs on the PIC, as shown in Figure 1a. Once the light from the telescope pupil is coupled onto the PIC, the interferometer mesh can be controlled by tuning thermal phase shifters in each interferometer to implement a mode-sorting algorithm in order to separate the starlight and planet light modes at high contrast levels. An integrated photonic testbed at NASA Ames Research Center is being developed to demonstrate coupling from a realistic telescope pupil into the PIC and will be used to characterize the contrast, throughput, and optical bandwidth of the coronagraph instrument. Figure 1b shows the design of the testbed, which will be used to experiment with different control algorithms for setting the tunable phase shifters in the photonic mesh and assess the factors limiting contrast on the chip to inform future iterations of the PIC design. Figure 1: (a) Diagram of AstroPIC instrument concept coupling the Habitable Worlds Observatory (HWO) pupil into an array of grating couplers using a microlens array. A mesh of Mach Zehnder Interferometers (MZIs) are tuned to separate starlight spatial modes from planet spatial modes. (b) Design of integrated photonics testbed under development at NASA Ames Research Center. The AstroPIC project has also developed simulations of the PIC coronagraph instrument concept in order to predict the coupling from the telescope pupil into the chip and simulate the photonic mesh behavior. Specifically, we are studying the application of the AstroPIC instrument concept to the NASA Habitable Worlds Observatory (HWO) flagship mission, which is currently in the pre-design phase. These simulations have shown that the AstroPIC concept is very robust to telescope pupil shape and aberrations for both on- and off-axis telescope configurations, and that the potential science yield of the AstroPIC coronagraph is very high even for relatively small numbers of input couplers. We find that the AstroPIC concept is particularly advantageous for accessing planets located at small inner working angles relative to the host star, which is extremely challenging for traditional coronagraph designs. Figure 2 shows these simulation results for an example HWO-like pupil, summarizing the predicted exo-Earth science yield as a function of (a) number of PIC input grating coupler channels, (b) starlight suppression order, and (c) end to end transmission efficiency. Figure 2: Predicted number of exo-Earths characterized over the HWO mission lifetime as a function of (a) number of input grating coupler PIC channels, (b) PIC starlight suppression order (number of output channels that are designated as starlight vs signal light), and (c) end-to-end transmission efficiency of the PIC instrument. These simulations are conducted using the FRIDAY yield calculation package.In this presentation, we will describe the AstroPIC instrument concept and how programmable photonics can be used to implement the optimal coronagraph operator. We will then present the development of an integrated photonics testbed at NASA Ames Research Center, which is being built to demonstrate the AstroPIC concept with a realistic telescope pupil directly coupled into the integrated photonic instrument. We will also review recent simulation results predicting the performance of next-generation AstroPIC instrument designs. Finally, we will discuss the next steps needed to mature this technology for future space telescope missions and ground telescope applications, including incorporating novel photonic component designs into the mesh architecture to improve the throughput and optical bandwidth of the instrument.

Abstract We report an observation of a transit of the hot Jupiter (HJ) KELT-23A b with the Keck Planet Finder spectrograph and a measurement of the sky-projected obliquity (λ) of its Sun-like (T eff ≈ 5900 K) host star. We measured a projected stellar obliquity of λ ≈ 180°, indicating that the orbit of the HJ is retrograde relative to the direction of the stellar spin. Due to the slow sky-projected rotational velocity of the host star ( v sin i ⋆ ≈ 0.5 km s−1), the true orbit of the HJ could be closer to polar. HJs around stars with effective temperatures below the Kraft break—such as KELT-23A—are generally found to have prograde orbits that are well-aligned with the equatorial planes of their host stars (i.e., λ ∼ 0°), most likely due to spin–orbit realignment driven by stellar tidal dissipation. This system is therefore a unique outlier that strains migration and tidal theories. The fact that the HJ has a highly misaligned orbit may suggest that the planet arrived at its close-in orbit relatively recently, possibly via interactions with the wide-separation (570 au) M-dwarf companion in the system, or that it has stalled near an antialigned or polar orientation while realigning. Using Gaia DR3, we determined the orbit of the stellar companion to be moderately face-on (γ = 60° ± 4°). We show that the distribution of observed systems in the γ–λ plane can be broadly reproduced using a toy model in which the orbits of the planetary and stellar companions begin aligned with the equatorial plane of the primary star and, upon migrating inwards, the planet preferentially obtains either an aligned or polar orbit.

Abstract The Wide Angle Search for Planets (WASP) survey provided some of the first transiting hot Jupiter candidates. With the addition of the Transiting Exoplanet Survey Satellite (TESS), many WASP planet candidates have now been revisited and given updated transit parameters. Here, we present nine transiting planets orbiting FGK stars that were identified as candidates by the WASP survey and found to have planetary masses via radial velocity measurements. Subsequent space-based photometry taken by TESS as well as ground-based photometric and spectroscopic measurements have been used to jointly analyze the planetary properties of WASP-102 b, WASP-116 b, WASP-149 b WASP-154 b, WASP-155 b, WASP-188 b, WASP-194 b/HAT-P-71 b, WASP-195 b, and WASP-197 b. These planets have radii between 0.9 R Jup and 1.4 R Jup, masses between 0.1 M Jup and 1.5 M Jup, and periods between 1.3 and 6.6 days.