arXiv subjects

Kazumasa Ohno

Publications and source records attributed to Kazumasa Ohno.

At least 55 records · Page 3Linked to original sources

arXiv2023

Stability and detectability of exomoons orbiting HIP 41378 f, a temperate Jovian planet with an anomalously low apparent density

Moons orbiting exoplanets ("exomoons") may hold clues about planet formation, migration, and habitability. In this work, we investigate the plausibility of exomoons orbiting the temperate ($T_\text{eq}=294$ K) giant ($R = 9.2$ R$_\oplus$) planet HIP 41378 f, which has been shown to have a low apparent bulk density of $0.09\,\text{g}\,\text{cm}^{-3}$ and a flat near-infrared transmission spectrum, hinting that it may possess circumplanetary rings. Given this planet's long orbital period ($P\approx1.5$ yr), it has been suggested that it may also host a large exomoon. Here, we analyze the orbital stability of a hypothetical exomoon with a satellite-to-planet mass ratio of 0.0123 orbiting HIP 41378 f. Combining a new software package, astroQTpy, with REBOUND and EqTide, we conduct a series of N-body and tidal migration simulations, demonstrating that satellites up to this size are largely stable against dynamical escape and collisions. We simulate the expected transit signal from this hypothetical exomoon and show that current transit observations likely cannot constrain the presence of exomoons orbiting HIP 41378 f, though future observations may be capable of detecting exomoons in other systems. Finally, we model the combined transmission spectrum of HIP 41378 f and a hypothetical moon with a low-metallicity atmosphere, and show that the total effective spectrum would be contaminated at the $\sim$10 ppm level. Our work not only demonstrates the feasibility of exomoons orbiting HIP 41378 f, but also shows that large exomoons may be a source of uncertainty in future high-precision measurements of exoplanet systems.

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arXiv2023

Nitrogen as a Tracer of Giant Planet Formation. II.: Comprehensive Study of Nitrogen Photochemistry and Implications for Observing NH3 and HCN in Transmission and Emission Spectra

Atmospheric nitrogen may provide important constraints on giant planet formation. Following our semi-analytical work (Ohno & Fortney 2022), we further pursue the relation between observable NH3 and an atmosphere's bulk nitrogen abundance by applying the photochemical kinetics model VULCAN across planetary equilibrium temperature, mass, age, eddy diffusion coefficient, atmospheric composition, and stellar spectral type. We confirm that the quenched NH3 abundance coincides with the bulk nitrogen abundance only at sub-Jupiter mass (< 1MJ) planets and old ages (> 1 Gyr) for solar composition atmospheres, highlighting important caveats for inferring atmospheric nitrogen abundances. Our semi-analytical model reproduces the quenched NH3 abundance computed by VULCAN and thus helps to infer the bulk nitrogen abundance from a retrieved NH3 abundance. By computing transmission and emission spectra, we predict that the equilibrium temperature range of 400--1000 K is optimal for detecting NH3 because NH3 depletion by thermochemistry and photochemistry is significant at hotter planets whereas entire spectral features become weak at colder planets. For Jupiter-mass planets around Sun-like stars in this temperature range, NH3 leaves observable signatures of $\sim$ 50 ppm at 1.5, 2.1, and 11 $\rm μm$ in transmission spectra and > 300--100 ppm at 6 $\rm μm$ and 11 $\rm μm$ in emission spectra. The photodissociation of NH3 leads HCN to replace NH3 at low pressures. However, the low HCN column densities lead to much weaker absorption features than for NH3. The NH3 features are readily accessible to JWST observations to constrain atmospheric nitrogen abundances, which may open a new avenue to understand the formation processes of giant exoplanets.

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arXiv2023

Methane Throughout the Atmosphere of the Warm Exoplanet WASP-80b

The abundances of major carbon and oxygen bearing gases in the atmospheres of giant exoplanets provide insights into atmospheric chemistry and planet formation processes. Thermochemistry suggests that methane should be the dominant carbon-bearing species below $\sim$1000 K over a range of plausible atmospheric compositions; this is the case for the Solar System planets and has been confirmed in the atmospheres of brown dwarfs and self-luminous directly imaged exoplanets. However, methane has not yet been definitively detected with space-based spectroscopy in the atmosphere of a transiting exoplanet, but a few detections have been made with ground-based, high-resolution transit spectroscopy including a tentative detection for WASP-80b. Here we report transmission and emission spectra spanning 2.4-4.0 micrometers of the 825 K warm Jupiter WASP-80b taken with JWST's NIRCam instrument, both of which show strong evidence for methane at greater than 6-sigma significance. The derived methane abundances from both viewing geometries are consistent with each other and with solar to sub-solar C/O and ~5$\times$ solar metallicity, which is consistent with theoretical predictions.

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arXiv2023

GREX-PLUS Science Book

GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer) is a mission candidate for a JAXA's strategic L-class mission to be launched in the 2030s. Its primary sciences are two-fold: galaxy formation and evolution and planetary system formation and evolution. The GREX-PLUS spacecraft will carry a 1.2 m primary mirror aperture telescope cooled down to 50 K. The two science instruments will be onboard: a wide-field camera in the 2-8 $μ$m wavelength band and a high resolution spectrometer with a wavelength resolution of 30,000 in the 10-18 $μ$m band. The GREX-PLUS wide-field camera aims to detect the first generation of galaxies at redshift $z>15$. The GREX-PLUS high resolution spectrometer aims to identify the location of the water ``snow line'' in proto-planetary disks. Both instruments will provide unique data sets for a broad range of scientific topics including galaxy mass assembly, origin of supermassive blackholes, infrared background radiation, molecular spectroscopy in the interstellar medium, transit spectroscopy for exoplanet atmosphere, planetary atmosphere in the Solar system, and so on.

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arXiv2023

Photochemically-produced SO$_2$ in the atmosphere of WASP-39b

Photochemistry is a fundamental process of planetary atmospheres that regulates the atmospheric composition and stability. However, no unambiguous photochemical products have been detected in exoplanet atmospheres to date. Recent observations from the JWST Transiting Exoplanet Early Release Science Program found a spectral absorption feature at 4.05 $μ$m arising from SO$_2$ in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass (0.28 M$_J$) gas giant exoplanet orbiting a Sun-like star with an equilibrium temperature of $\sim$1100 K. The most plausible way of generating SO$_2$ in such an atmosphere is through photochemical processes. Here we show that the SO$_2$ distribution computed by a suite of photochemical models robustly explains the 4.05 $μ$m spectral feature identified by JWST transmission observations with NIRSpec PRISM (2.7$σ$) and G395H (4.5$σ$). SO$_2$ is produced by successive oxidation of sulphur radicals freed when hydrogen sulphide (H$_2$S) is destroyed. The sensitivity of the SO$_2$ feature to the enrichment of the atmosphere by heavy elements (metallicity) suggests that it can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an inferred metallicity of $\sim$10$\times$ solar. We further point out that SO$_2$ also shows observable features at ultraviolet and thermal infrared wavelengths not available from the existing observations.

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arXiv2023

A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b

Close-in giant exoplanets with temperatures greater than 2,000 K (''ultra-hot Jupiters'') have been the subject of extensive efforts to determine their atmospheric properties using thermal emission measurements from the Hubble and Spitzer Space Telescopes. However, previous studies have yielded inconsistent results because the small sizes of the spectral features and the limited information content of the data resulted in high sensitivity to the varying assumptions made in the treatment of instrument systematics and the atmospheric retrieval analysis. Here we present a dayside thermal emission spectrum of the ultra-hot Jupiter WASP-18b obtained with the NIRISS instrument on JWST. The data span 0.85 to 2.85 $μ$m in wavelength at an average resolving power of 400 and exhibit minimal systematics. The spectrum shows three water emission features (at $>$6$σ$ confidence) and evidence for optical opacity, possibly due to H$^-$, TiO, and VO (combined significance of 3.8$σ$). Models that fit the data require a thermal inversion, molecular dissociation as predicted by chemical equilibrium, a solar heavy element abundance (''metallicity'', M/H = 1.03$_{-0.51}^{+1.11}$ $\times$ solar), and a carbon-to-oxygen (C/O) ratio less than unity. The data also yield a dayside brightness temperature map, which shows a peak in temperature near the sub-stellar point that decreases steeply and symmetrically with longitude toward the terminators.

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arXiv2022

Nitrogen as a Tracer of Giant Planet Formation. I.: A Universal Deep Adiabatic Profile and Semi-analytical Predictions of Disequilibrium Ammonia Abundances in Warm Exoplanetary Atmospheres

A major motivation of spectroscopic observations of giant exoplanets is to unveil planet formation processes from atmospheric compositions. Several recent studies suggested that atmospheric nitrogen, like carbon and oxygen, can provide important constrains on planetary formation environments. Since nitrogen chemistry can be far from thermochemical equilibrium in warm atmospheres, we extensively investigate under what conditions, and with what assumptions, the observable NH3 abundances can diagnose an atmosphere's bulk nitrogen abundance. In the first paper of this series, we investigate atmospheric T-P profiles across equilibrium temperature, surface gravity, intrinsic temperature, atmospheric metallicity, and C/O ratio using a 1D radiative-convective equilibrium model. Models with the same intrinsic temperature and surface gravity coincide with a shared "universal" adiabat in the deep atmosphere, across a wide equilibrium temperature range (250--1200 K), which is not seen in hotter or cooler models. We explain this behavior in terms of the classic "radiative zero solution" and then establish a semi-analytical T-P profile of the deep atmospheres of warm exoplanets. This profile is then used to predict vertically quenched NH3 abundances. At solar metallicity, our results show that the quenched NH3 abundance only coincides with the bulk nitrogen abundance (within 10%) at low intrinsic temperature, corresponding to a planet with a sub-Jupiter mass (< 1 MJ) and old age (> 1 Gyr). If a planet has a high metallicity ($\ge$ 10$\times$ solar) atmosphere, the quenched NH3 abundance significantly underestimates the bulk nitrogen abundance at almost all planetary masses and ages. We suggest modeling and observational strategies to improve the assessment of bulk nitrogen from NH3.

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arXiv2022

Early Release Science of the exoplanet WASP-39b with JWST NIRCam

Measuring the metallicity and carbon-to-oxygen (C/O) ratio in exoplanet atmospheres is a fundamental step towards constraining the dominant chemical processes at work and, if in equilibrium, revealing planet formation histories. Transmission spectroscopy provides the necessary means by constraining the abundances of oxygen- and carbon-bearing species; however, this requires broad wavelength coverage, moderate spectral resolution, and high precision that, together, are not achievable with previous observatories. Now that JWST has commenced science operations, we are able to observe exoplanets at previously uncharted wavelengths and spectral resolutions. Here we report time-series observations of the transiting exoplanet WASP-39b using JWST's Near InfraRed Camera (NIRCam). The long-wavelength spectroscopic and short-wavelength photometric light curves span 2.0 - 4.0 $μ$m, exhibit minimal systematics, and reveal well-defined molecular absorption features in the planet's spectrum. Specifically, we detect gaseous H$_2$O in the atmosphere and place an upper limit on the abundance of CH$_4$. The otherwise prominent CO$_2$ feature at 2.8 $μ$m is largely masked by H$_2$O. The best-fit chemical equilibrium models favour an atmospheric metallicity of 1-100$\times$ solar (i.e., an enrichment of elements heavier than helium relative to the Sun) and a sub-stellar carbon-to-oxygen (C/O) ratio. The inferred high metallicity and low C/O ratio may indicate significant accretion of solid materials during planet formation or disequilibrium processes in the upper atmosphere.

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arXiv2022

Early Release Science of the Exoplanet WASP-39b with JWST NIRSpec G395H

Measuring the abundances of carbon and oxygen in exoplanet atmospheres is considered a crucial avenue for unlocking the formation and evolution of exoplanetary systems. Access to an exoplanet's chemical inventory requires high-precision observations, often inferred from individual molecular detections with low-resolution space-based and high-resolution ground-based facilities. Here we report the medium-resolution (R$\sim$600) transmission spectrum of an exoplanet atmosphere between 3-5 $μ$m covering multiple absorption features for the Saturn-mass exoplanet WASP-39b, obtained with JWST NIRSpec G395H. Our observations achieve 1.46x photon precision, providing an average transit depth uncertainty of 221 ppm per spectroscopic bin, and present minimal impacts from systematic effects. We detect significant absorption from CO$_2$ (28.5$σ$) and H$_2$O (21.5$σ$), and identify SO$_2$ as the source of absorption at 4.1 $μ$m (4.8$σ$). Best-fit atmospheric models range between 3 and 10x solar metallicity, with sub-solar to solar C/O ratios. These results, including the detection of SO$_2$, underscore the importance of characterising the chemistry in exoplanet atmospheres, and showcase NIRSpec G395H as an excellent mode for time series observations over this critical wavelength range.

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arXiv2022

Early Release Science of the exoplanet WASP-39b with JWST NIRISS

Transmission spectroscopy provides insight into the atmospheric properties and consequently the formation history, physics, and chemistry of transiting exoplanets. However, obtaining precise inferences of atmospheric properties from transmission spectra requires simultaneously measuring the strength and shape of multiple spectral absorption features from a wide range of chemical species. This has been challenging given the precision and wavelength coverage of previous observatories. Here, we present the transmission spectrum of the Saturn-mass exoplanet WASP-39b obtained using the SOSS mode of the NIRISS instrument on the JWST. This spectrum spans $0.6 - 2.8 μ$m in wavelength and reveals multiple water absorption bands, the potassium resonance doublet, as well as signatures of clouds. The precision and broad wavelength coverage of NIRISS-SOSS allows us to break model degeneracies between cloud properties and the atmospheric composition of WASP-39b, favoring a heavy element enhancement ("metallicity") of $\sim 10 - 30 \times$ the solar value, a sub-solar carbon-to-oxygen (C/O) ratio, and a solar-to-super-solar potassium-to-oxygen (K/O) ratio. The observations are best explained by wavelength-dependent, non-gray clouds with inhomogeneous coverage of the planet's terminator.

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arXiv2022

A Circumplanetary Dust Ring May Explain the Extreme Spectral Slope of the 10 Myr Young Exoplanet K2-33b

Young exoplanets are attractive targets for atmospheric characterization to explore the early phase of planetary evolution and the surrounding environment. Recent observations of the 10 Myr young Neptune-sized exoplanet K2-33b revealed that the planet's transit depth drastically decreases from the optical to near-infrared wavelengths. Thao et al. (2022) suggested that a thick planetary haze and/or stellar spots may be the cause; however, even the best-fit model only barely explains the data. Here, we propose that the peculiar transmission spectrum may indicate that K2-33b possess a circumplanetary dust ring, an analog of Jupiter's dust ring. We demonstrate that the ring could produce a steep slope in the transmission spectrum even if its optical depth is as low as $\sim {10}^{-2}$. We then apply a novel joint atmosphere-ring retrieval to K2-33b and find that the ring scenario could well explain the observed spectrum for various possible ring compositions. Importantly, the dust ring also exhibits prominent absorption features of ring particles around $\sim$10 $\rmμm$, whose shape and strength depend on the composition of the ring. Thus, future observations by JWST-MIRI would be able to test not only the ring hypothesis but also, if it indeed exists, to constrain the composition of the ring -- providing a unique opportunity to explore the origins of the dust ring around its parent planet, soon after the planetary system's formation.

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arXiv2022

Identification of carbon dioxide in an exoplanet atmosphere

Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (i.e., elements heavier than helium, also called "metallicity"), and thus formation processes of the primary atmospheres of hot gas giants. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets. Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2 but have not yielded definitive detections due to the lack of unambiguous spectroscopic identification. Here we present the detection of CO2 in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science Program (ERS). The data used in this study span 3.0 to 5.5 μm in wavelength and show a prominent CO2 absorption feature at 4.3 μm (26σ significance). The overall spectrum is well matched by one-dimensional, 10x solar metallicity models that assume radiative-convective-thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide, and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0 μm that is not reproduced by these models.

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arXiv2022

The Molecular Composition of Shadowed Protosolar Disk Midplanes beyond the Water Snowline

The disk midplane temperature is potentially affected by the dust traps/rings. The dust depletion beyond the water snowline will cast a shadow. In this study, we adopt a detailed gas-grain chemical reaction network, and investigate the radial gas and ice abundance distributions of dominant carbon-, oxygen-, and nitrogen-bearing molecules in disks with shadow structures beyond the water snowline around a protosolar-like star. In shadowed disks, the dust grains at around $3-8$ au are predicted to have more than around $5-10$ times amounts of ices of organic molecules such as H$_{2}$CO, CH$_{3}$OH, and NH$_{2}$CHO, saturated hydrocarbon ices such as CH$_{4}$ and C$_{2}$H$_{6}$, in addition to H$_{2}$O, CO, CO$_{2}$, NH$_{3}$, N$_{2}$, and HCN ices, compared with those in non-shadowed disks. In the shadowed regions, we find that hydrogenation (especially of CO ice) is the dominant formation mechanism of complex organic molecules. The gas-phase N/O ratios show much larger spatial variations than the gas-phase C/O ratios, thus the N/O ratio is predicted to be a useful tracer of the shadowed region. N$_{2}$H$^{+}$ line emission is a potential tracer of the shadowed region. We conclude that a shadowed region allows the recondensation of key volatiles onto dust grains, provides a region of chemical enrichment of ices that is much closer to the star than within a non-shadowed disk, and may explain to some degree the trapping of O$_{2}$ ice in dust grains that formed comet 67P/Churyumov-Gerasimenko. We discuss that, if formed in a shadowed disk, Jupiter does not need to have migrated vast distances.

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arXiv2022

Cleaning our Hazy Lens: Exploring Trends in Transmission Spectra of Warm Exoplanets

Relatively little is understood about the atmospheric composition of temperate to warm exoplanets (equilibrium temperature $T_{\rm eq}<$ 1000 K), as many of them are found to have uncharacteristically flat transmission spectra. Their flattened spectra are likely due to atmospheric opacity sources such as planet-wide photochemical hazes and condensation clouds. We compile the transmission spectra of 25 warm exoplanets previously observed by the Hubble Space Telescope and quantify the haziness of each exoplanet using a normalized amplitude of the water absorption feature ($A_{\rm H}$). By examining the relationships between $A_{\rm H}$ and various planetary and stellar forcing parameters, we endeavor to find correlations of haziness associated with planetary properties. We adopt new statistical correlation tests that are more suitable for the small, non-normally distributed warm exoplanet sample. Our analysis shows that none of the parameters hold statistically significant correlation with $A_{\rm H}$ ($p \le 0.01$) with the addition of new exoplanet data, including the previously identified linear trends between $A_{\rm H}$ and $T_{\rm{eq}}$ or hydrogen-helium envelope mass fraction (f$_{\rm{HHe}}$). This suggests that haziness in warm exoplanets is not simply controlled by any single planetary/stellar parameter. Among all the parameters we investigated, planet gravity ($g_{\rm p}$), atmospheric scale height ($H$), planet density ($ρ_{\rm p}$), orbital eccentricity ($e$), and age of the star ($t_{\rm age}$) hold tentative correlations with $A_{\rm H}$. Specifically, lower $H$, higher $g_{\rm p}$, $ρ_{\rm p}$, $e$, or $t_{\rm age}$ may lead to clearer atmospheres. We still need more observations and laboratory experiments to fully understand the complex physics and chemistry involved in creating hazy warm exoplanets.

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arXiv2022

A Framework for Characterizing Transmission Spectra of Exoplanets with Circumplanetary Rings

Recent observations revealed that several extremely low-density exoplanets show featureless transmission spectra. While atmospheric aerosols are a promising explanation for both the low density and featureless spectra, there is another attractive possibility: the presence of circumplanetary rings. Previous studies suggested that rings cause anomalously large transit radii. However, it remains poorly understood how rings affect the transmission spectrum. Here, we provide a framework to characterize the transmission spectra of ringed exoplanets. We develop an analytical prescription to include rings in the transmission spectra for arbitrarily viewing geometries. We also establish a simple post-processing model that can include the ring's effects on precomputed ring-free spectra. The ring flattens the transmission spectrum for a wide range of viewing geometries, consistent with the featureless spectra of extremely low-density exoplanets. Near-future observations by JWST at longer wavelengths would be able to distinguish the aerosol and ring scenarios. We also find that rocky rings might cause a silicate feature at $\sim$10 $μ$m if the ring's optical depth is around unity. Thus, the ring's spectral features, if detected, would provide tight constrains on the physical properties of exoplanetary rings. We also discuss the ring's stability and suggest that thick rings are sustainable only at the equilibrium temperature of $\lesssim$300 K for the ring's age comparable to Kepler planets. This might indicate the intrinsic deficit of thick rings in the Kepler samples, unless rings are much younger than the planets as suggested for Saturn.

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arXiv2022

The First Near-Infrared Transmission Spectrum of HIP 41378 f, a Low-Mass Temperate Jovian World in a Multi-Planet System

We present a near-infrared transmission spectrum of the long period (P=542 days), temperate ($T_{eq}$=294 K) giant planet HIP 41378 f obtained with the Wide-Field Camera 3 (WFC3) instrument aboard the Hubble Space Telescope (HST). With a measured mass of 12 $\pm$ 3 $M_{\oplus}$ and a radius of 9.2 $\pm$ 0.1 $R_{\oplus}$, HIP 41378 f has an extremely low bulk density (0.09 $\pm$ 0.02 g/cm$^{3}$). We measure the transit depth with a median precision of 84 ppm in 30 spectrophotometric channels with uniformly-sized widths of 0.018 microns. Within this level of precision, the spectrum shows no evidence of absorption from gaseous molecular features between 1.1-1.7 microns. Comparing the observed transmission spectrum to a suite of 1D radiative-convective-thermochemical-equilibrium forward models, we rule out clear, low-metallicity atmospheres and find that the data prefer high-metallicity atmospheres or models with an additional opacity source such as high-altitude hazes and/or circumplanetary rings. We explore the ringed scenario for this planet further by jointly fitting the K2 and HST light curves to constrain the properties of putative rings. We also assess the possibility of distinguishing between hazy, ringed, and high-metallicity scenarios at longer wavelengths with JWST. HIP 41378 f provides a rare opportunity to probe the atmospheric composition of a cool giant planet spanning the gap between the Solar System giants, directly imaged planets, and the highly-irradiated hot Jupiters traditionally studied via transit spectroscopy.

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arXiv2021

Grain Growth in Escaping Atmospheres: Implications for the Radius Inflation of Super-Puffs

Super-puffs -- low-mass exoplanets with extremely low bulk density -- are attractive targets for exploring their atmospheres and formation processes. Recent studies suggested that the large radii of super-puffs may be caused by atmospheric dust entrained in the escaping atmospheres. In this study, we investigate how the dust grows in escaping atmospheres and influence the transit radii using a microphysical model of grain growth. Collision growth is efficient in many cases, leading to hinder the upward transport of dust via enhanced gravitational settling. We find that dust abundance in the outflow hardly exceeds the Mach number at the dust production region. Thus, dust formed at upper atmospheres, say $P\lesssim{10}^{-5}$ bar, are needed to launch a dusty outflow with high dust abundance. With sufficiently high dust production altitudes and rates, the dusty outflow can enhance the observable radius by a factor of $\sim$2 or even more. We suggest that photochemical haze is a promising candidate of high-altitude dust that can be entrained in the outflow. We also compute the synthetic transmission spectra of super-puff atmospheres and demonstrate that the dusty outflow produces a broad spectral slope and obscures molecular features, in agreement with recently reported featureless spectra. Lastly, using an interior structure model, we suggest that the atmospheric dust could drastically enhance the observable radius only for planets in a narrow mass range of $\sim2$--$5M_{\rm \oplus}$, in which the boil-off tends to cause total atmospheric loss. This may explain why super-puffs are uncommon despite the suggested universality of photochemical hazes.

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arXiv2021

Jupiter's "Cold" Formation in the Protosolar Disk Shadow: An Explanation for the Planet's Uniformly Enriched Atmosphere

Atmospheric compositions offer valuable clues to planetary formation and evolution. Jupiter has been the most well-studied giant planet in terms of its atmosphere; however, the origin of the Jovian atmospheric composition remains a puzzle as the abundances of nitrogen and noble gases as high as those of other elements could only originate from extremely cold environments. We propose a novel idea for explaining the Jovian atmospheric composition: Dust pileup at the H$_2$O snow line casts a shadow and cools the Jupiter orbit so that N$_2$ and noble gases can freeze. Planetesimals or a core formed in the shadowed region can enrich nitrogen and noble gases as much as other elements through their dissolution in the envelope. We compute the temperature structure of a shadowed protosolar disk with radiative transfer calculations. Then, we investigate the radial volatile distributions and predict the atmospheric composition of Jupiter with condensation calculations. We find that the vicinity of the current Jupiter orbit, approximately $3$--$7~{\rm AU}$, could be as cold as $30~{\rm K}$ if the small-dust surface density varies by a factor of $\gtrsim30$ across the H$_2$O snow line. According to previous grain growth simulations, this condition could be achieved by weak disk turbulence if silicate grains are more fragile than icy grains. The shadow can cause the condensation of most volatile substances, namely N$_2$ and Ar. We demonstrate that the dissolution of shadowed solids can explain the elemental abundance patterns of the Jovian atmosphere even if proto-Jupiter was formed near Jupiter's current orbit. The disk shadow may play a vital role in controlling atmospheric compositions. The effect of the shadow also impacts the interpretation of upcoming observations of exoplanetary atmospheres by JWST.

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