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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Kinematic and thermal signatures of the directly imaged protoplanet candidate around Elias 2−24

We report kinematic and thermal signatures associated with the directly imaged protoplanet candidate in the Elias 2–24 disc. Using the DSHARP (Disc Substructures at High Angular Resolution Project) ALMA (Atacama Large Millimetre/submillimetre Array) observations of the 12 CO J = 2 − 1 line, we show that the disc kinematics are perturbed, with a detached CO emission spot at the location of the planet candidate and traces of spiral wakes, and also that the observed CO emission intensities require local heating. While the foreground extinction hides the velocity channels associated with the planet, preventing a planet mass estimate, the level of gas heating implied by the CO emission indicates the presence of a warm, embedded giant planet. Comparison with models shows that this could either be a ≳5 M Jup or a lower mass (≳2 M Jup ) but accreting protoplanet.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Effects of turbulent diffusion and back-reaction on the dust distribution around two resonant planets

In evolved and dusty circumstellar discs, two planets with masses comparable to Jupiter and Saturn that migrate outwards while maintaining an orbital resonance can produce distinctive features in the dust distribution. Dust accumulates at the outer edge of the common gas gap, which behaves as a dust trap, where the local dust concentration is significantly enhanced by the planets’ outward motion. Concurrently, an expanding cavity forms in the dust distribution inside the planets’ orbits, because dust does not filter through the common gaseous gap and grain depletion in the region continues via inward drifting. There is no cavity in the gas distribution because gas can filter through the gap, although ongoing gas accretion on the planets can reduce the gas density in the inner disc. Such behaviour was demonstrated by means of simulations neglecting the effects of dust diffusion due to turbulence and of dust backreaction on the gas. Both effects may alter the formation of the dust peak at the gap outer edge and of the inner dust cavity, by letting grains filter through the dust trap. We performed high-resolution hydrodynamical simulations of the coupled evolution of gas and dust species, the latter treated as pressureless fluids, in the presence of two giant planets. We show that diffusion and backreaction can change some morphological aspects of the dust distribution but do not alter some main features, such as the outer peak and the expanding inner cavity. Furthermore, these findings are confirmed for different parametrizations of gas viscosity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Giant Planet Scatterings and Collisions: Hydrodynamics, Merger-Ejection Branching Ratio, and Properties of the Remnants

Planetary systems with sufficiently small orbital spacings can experience planetary mergers and ejections. The branching ratio of mergers vs ejections depends sensitively on the treatment of planetary close encounters. Previous works have adopted a simple “sticky-sphere” prescription, whose validity is questionable. We apply both smoothed particle hydrodynamics and N-body integrations to investigate the fluid effects in close encounters between gas giants and the long-term evolution of closely-packed planetary systems. Focusing on parabolic encounters between Jupiter-like planets with MJ and 2MJ, we find that quick mergers occur when the impact parameter rp (the pericenter separation between the planets) is less than 2RJ, and the merger conserved at least 97% of the initial mass. Strong tidal effects can affect the “binary-planet” orbit when rp is between 2RJ and 4RJ. We quantify these effects using a set of fitting formulae that can be implemented in N-body codes. We run a suite of N-body simulations with and without the formulae for systems of two giant planets initially in unstable, nearly circular and nearly coplanar orbits. The fluid (tidal) effects significantly increase the branching ratio of planetary mergers relative to ejections by doubling the effective collision radius. While the fluid effects do not change the distributions of semi-major axis and eccentricity of each type of remnant planets (mergers vs surviving planets in ejections), the overall orbital properties of planet scattering remnants are strongly affected due to the branching ratio change. We also find that the merger products have broad distributions of spin magnitudes and obliquities.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

ACCESS: An Optical Transmission Spectrum of the High-gravity Hot Jupiter HAT-P-23b

We present a new ground-based visible transmission spectrum of the high-gravity, hot Jupiter HAT-P-23b, obtained as part of the ACCESS project. We derive the spectrum from five transits observed between 2016 and 2018, with combined wavelength coverage between 5200 Å and 9269 Å in 200 Å bins, and with a median precision of 247 ppm per bin. HAT-P-23b’s relatively high surface gravity (g ≈ 30 m s{sup −2}), combined with updated stellar and planetary parameters from Gaia DR2, gives a five-scale-height signal of 384 ppm for a hydrogen-dominated atmosphere. Bayesian models favor a clear atmosphere for the planet with the tentative presence of TiO, after simultaneously modeling stellar contamination, using spots parameter constraints from photometry. If confirmed, HAT-P-23b would be the first example of a high-gravity gas giant with a clear atmosphere observed in transmission at optical/near-IR wavelengths; therefore, we recommend expanding observations to the UV and IR to confirm our results and further characterize this planet. This result demonstrates how combining transmission spectroscopy of exoplanet atmospheres with long-term photometric monitoring of the host stars can help disentangle the exoplanet and stellar activity signals.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Second-generation dust in planetary systems: the case of HD 163296

Observations indicate that large, dust-laden protoplanetary discs are common. Some features, like gaps, rings, and spirals, suggest they may host young planets, which can excite the orbits of nearby leftover planetesimals. Energetic collisions among these bodies can lead to the production of second-generation dust. Grains produced by collisions may have a dynamical behaviour different from that of first-generation, primordial dust out of which planetesimals and planets formed. Here, we aim to study these differences for the HD 163296 system and determine whether dynamical signatures in the mixture of the two dust populations can help separate their contributions. We use three-dimensional (3D) hydrodynamic models to describe the gaseous disc with three, Saturn- to Jupiter-mass, embedded planets. Dust grains, of sizes $1\, \mu \mathrm{m}$–$1\, \mathrm{mm}$, are treated as Lagrangian particles with resolved thermodynamics and mass-loss. Initial disc and planet configurations are derived from observation-based work, which indicates low gas viscosity. The 3D approach also allows us to detect the formation of vortices induced by Rossby waves, where dust becomes concentrated and may contribute to planetesimal formation. We find that the main differences in the dynamical behaviour of first- and second-generation dust occur in the vertical distribution. The two populations have similar distributions around the disc mid-plane, although second-generation dust shows longer residence times close to the radial locations of the planets’ gas gaps. Sedimentation rates of $\mu$m-sized grains are comparable to or lower than the production rates by planetesimals’ collisions, making this population potentially observable. These outcomes can be extended to similar systems harbouring giant planets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Dust supply to close binary systems

Binary systems can be born surrounded by circumbinary discs. The gaseous disc around either of the two stellar companions can have its life extended by the supply of mass arriving from the circumbinary disc. The objective of this study is to investigate the gravitational interactions exerted by a compact and eccentric binary system on the circumbinary and circumprimary discs, and the resulting transport of gas and solids between the disc components. We assume that the gas in the system behaves as a fluid, and we model its evolution by means of high-resolution hydrodynamical simulations. Dust grains are modelled as Lagrangian particles that interact with the gas and the stars. Our models indicate that significant fluxes of gas and dust proceed from the circumbinary disc towards the circumprimary disc. For the applied system parameters, grains of certain sizes are segregated outside the tidal gap generated by the stars. Consequently, the size distribution of the transported dust is not continuous, but presents a gap in the millimetre size range. In close binaries, the lifetime of an isolated circumprimary disc is found to be short, ~10 5 years, because of its low mass. However, because of the influx of gas from beyond the tidal gap, the disc around the primary star can survive much longer, ~10 6 years, as long as gas accretion from the circumbinary disc continues. The supply of solids and the extended lifetime of a circumbinary disc also aids in the possible formation of giant planets. Compared to close binary systems without a circumbinary disc, we expect a higher frequency of singleplanet or multiple-planet systems. Additionally, a planetesimal or debris belt can form in the proximity of the truncation radius of the circumprimary disc and/or around the location of the exterior edge of the tidal gap.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Accretion of Gas Giants Constrained by the Tidal Barrier

After protoplanets have acquired sufficient mass to open partial gaps in their natal protostellar disks, residual gas continues to diffuse onto horseshoe streamlines under the effect of viscous dissipation, and to meander in and out of the planets' Hill sphere. Within the Hill sphere, the horseshoe streamlines intercept gas flow in circumplanetary disks. The host star's tidal perturbation induces a barrier across the converging streamlines' interface. Viscous transfer of angular momentum across this tidal barrier determines the rate of mass diffusion from the horseshoe streamlines onto the circumplanetary disks, and eventually the accretion rate onto the protoplanets. Here, we carry out a series of numerical simulations to test the influence of this tidal barrier on superthermal planets. In weakly viscous disks, the protoplanets' accretion rate steeply decreases with their masses above the thermal limit. As their growth timescale exceeds the gas depletion timescale, their masses reach asymptotic values comparable to that of Jupiter. In relatively thick and strongly viscous disks, protoplanets' asymptotic masses exceed several times that of Jupiter. Two-dimensional numerical simulations show that such massive protoplanets strongly excite the eccentricity of nearby horseshoe streamlines, destabilize orderly flow, substantially enhance the diffusion rate across the tidal barrier, and elevate their growth rate until their natal disk is severely depleted. In contrast, eccentric streamlines remain stable in three-dimensional simulations. Based on the upper falloff in the observed mass distribution of known exoplanets, we suggest that their natal disks had relatively low viscosity (α ~ 10 –3 ) and modest thickness (H/R ~ 0.03–0.05).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

The Preservation of Super-Earths and the Emergence of Gas Giants after Their Progenitor Cores Have Entered the Pebble-isolation Phase

The omnipresence of super-Earths suggests that they are able to be retained in natal disks around low-mass stars, whereas exoplanets' mass distributions indicate that some cores have transformed into gas giants through runaway gas accretion at ≳1 au from solar-type stars. In this paper, we show that transition to runaway gas accretion by cores may be self-impeded by an increase of the grain opacity in their envelope after they have acquired sufficient mass (typically ~ 10M ⊕ ) to enter a pebble-isolation phase. The accumulation of approximately millimeter- to meter-sized pebbles in their migration barriers enhances their local fragmentation rates. The freshly produced submillimeter grains pass through the barrier, elevate the effective dust opacity, and reduce the radiative flux in the core's envelope. These effects alone are adequate to suppress the transition to runaway accretion and preserve super-Earths in the stellar proximity (~0.1 au), albeit entropy advection between the envelope and the disk can further reduce the accretion rate. At an intermediate distance (~1 au) from their host stars, the escalation in the dust opacity dominates over entropy advection in stalling the transition to runaway accretion for marginally pebble-isolated cores. Beyond a few astronomical unit, the transformation of more-massive cores to gas giants is reachable before severe depletion of disk gas. This requirement can be satisfied either in extended disks with large scale height via orderly accretion of migrating pebbles or through the mergers of oligarchic protoplanetary embryos, and can account for the correlated occurrence of long-period gas giants and close-in super-Earths.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

The Great Inequality and the Dynamical Disintegration of the Outer Solar System

Using an ensemble of N-body simulations, this paper considers the fate of the outer gas giants (Jupiter, Saturn, Uranus, and Neptune) after the Sun leaves the main sequence and completes its stellar evolution. Due to solar mass loss—which is expected to remove roughly half of the star’s mass—the orbits of the giant planets expand. This adiabatic process maintains the orbital period ratios, but the mutual interactions between planets and the width of mean-motion resonances (MMR) increase, leading to the capture of Jupiter and Saturn into a stable 5:2 resonant configuration. The expanded orbits, coupled with the large-amplitude librations of the critical MMR angle, make the system more susceptible to perturbations from stellar flyby interactions. Accordingly, within about 30 Gyr, stellar encounters perturb the planets onto the chaotic subdomain of the 5:2 resonance, triggering a large-scale instability, which culminates in the ejections of all but one planet over the subsequent ∼10 Gyr. After an additional ∼50 Gyr, a close stellar encounter (with a perihelion distance less than ∼200 au) liberates the final planet. Through this sequence of events, the characteristic timescale over which the solar system will be completely dissolved is roughly 100 Gyr. Our analysis thus indicates that the expected dynamical lifetime of the solar system is much longer than the current age of the universe, but is significantly shorter than previous estimates.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Ionization by XFEL radiation produces distinct structure in liquid water

In the warm dense matter (WDM) regime, where condensed, gas, and plasma phases coexist, matter frequently exhibits unusual properties that cannot be described by contemporary theory. Experiments reporting phenomena in WDM are therefore of interest to advance our physical understanding of this regime, which is found in dwarf stars, giant planets, and fusion ignition experiments. Using 7.1 keV X-ray free electron laser radiation (nominally 5×10 5 J/cm 2 ), we produced and probed transient WDM in liquid water. Wide-angle X-ray scattering (WAXS) from the probe reveals a new ~9 Å structure that forms within 75 fs. By 100 fs, the WAXS peak corresponding to this new structure is of comparable magnitude to the ambient water peak, which is attenuated. Simulations suggest that the experiment probes a superposition of two regimes. In the first, fluences expected at the focus severely ionize the water, which becomes effectively transparent to the probe. In the second, out-of-focus pump radiation produces O 1+ and O 2+ ions, which rearrange due to Coulombic repulsion over 10 s of fs. Our simulations account for a decrease in ambient water signal and an increase in low-angle X-ray scattering but not the experimentally observed 9 Å feature, presenting a new challenge for theory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Planetesimal Impact Vapor Plumes and Nebular Shocks Form Chondritic Mixtures

The origin of chondrules and the chondritic sedimentary rocks that dominate the meteoritic record is a long-standing problem in planetary science. Here, we develop a physical model for the formation of chondritic mixtures as an outcome of vaporizing collisions between planetesimals that were dynamically excited by the growth and migration of planets. We present calculations of nebular shock waves generated by impact vapor plumes and focus on aspects of the plume interaction with the nebular gas and dust that have been neglected in previous studies of impact ejecta. We find that when water dominates the vapor, the plumes are relatively cool. However, the plume expansion is supersonic and can drive strong shock waves in the dusty nebular gas. Portions of these nebular shock fronts initially melt nebular dust, forming chondrules that are coupled to the moving front. As the shock front expands and cools, the chondrules solidify, while the shock front entrains additional dust. Eventually, the plume expansion stalls and then hydrodynamically collapses, turbulently mixing variably processed dust and size-sorted chondrules. For probable impact parameters and nebular conditions during giant planet growth and migration, the impact-generated mixtures have characteristics that span the range observed in chondritic meteorites, providing an environment for rapid formation of chondritic assemblages after chondrule formation. Our impact vapor and nebular shocks model, named the IVANS model, links chondrule formation to the overall context of planet formation and provides a framework for interpreting the detailed chronological and geochemical record contained in chondritic meteorites.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

TOI-481 b and TOI-892 b: Two Long-period Hot Jupiters from the Transiting Exoplanet Survey Satellite

We present the discovery of two new 10 day period giant planets from the Transiting Exoplanet Survey Satellite mission, whose masses were precisely determined using a wide diversity of ground-based facilities. TOI-481 b and TOI-892 b have similar radii (0.99 ± 0.01 R{sub J} and 1.07 ± 0.02 R{sub J}, respectively), and orbital periods (10.3311 days and 10.6266 days, respectively), but significantly different masses (1.53 ± 0.03 M{sub J} versus 0.95 ± 0.07 M{sub J}, respectively). Both planets orbit metal-rich stars ([Fe/H] = +0.26±0.05 dex and [Fe/H] = +0.24±0.05 for TOI-481 and TOI-892, respectively) but at different evolutionary stages. TOI-481 is a M{sub ⋆} = 1.14 ± 0.02 M{sub ⊙}, R{sub ⋆} = 1.66 ± 0.02 R{sub ⊙} G-type star (T{sub eff} = 5735±72 K), that with an age of 6.7 Gyr, is in the turn-off point of the main sequence. TOI-892 on the other hand, is a F-type dwarf star (T{sub eff} = 6261±80 K), which has a mass of M{sub ⋆} = 1.28 ± 0.03 M{sub ⊙} and a radius of R{sub ⋆} = 1.39 ± 0.02 R{sub ⊙}. TOI-481 b and TOI-892 b join the scarcely populated region of transiting gas giants with orbital periods longer than 10 days, which is important to constrain theories of the formation and structure of hot Jupiters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Giant Outer Transiting Exoplanet Mass (GOT ‘EM) Survey. II. Discovery of a Failed Hot Jupiter on a 2.7 Yr, Highly Eccentric Orbit

Radial velocity (RV) surveys have discovered giant exoplanets on au-scale orbits with a broad distribution of eccentricities. Those with the most eccentric orbits are valuable laboratories for testing theories of high-eccentricity migration. However, few such exoplanets transit their host stars, thus removing the ability to apply constraints on formation from their bulk internal compositions. We report the discovery of Kepler-1704 b, a transiting 4.15 M {sub J} giant planet on a 988.88 day orbit with an extreme eccentricity of 0.921{sub -0.015}{sup +0.010}. Our decade-long RV baseline from the Keck I telescope allows us to measure the orbit and bulk heavy-element composition of Kepler-1704 b and place limits on the existence of undiscovered companions. A failed hot Jupiter, Kepler-1704 b was likely excited to high eccentricity by scattering events that possibly began during its gas accretion phase. Its final periastron distance was too large to allow for tidal circularization, so now it orbits its host from distances spanning 0.16–3.9 au. The maximum difference in planetary equilibrium temperature resulting from this elongated orbit is over 700 K. A simulation of the thermal phase curve of Kepler-1704 b during periastron passage demonstrates that it is a remarkable target for atmospheric characterization from the James Webb Space Telescope, which could potentially also measure the planet’s rotational period as the hot spot from periastron rotates in and out of view. Continued characterization of the Kepler-1704 system promises to refine theories explaining the formation of hot Jupiters and cool giant planets like those in the solar system.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey. II. Free-floating Planet Detection Rates

The Nancy Grace Roman Space Telescope (Roman) will perform a Galactic Exoplanet Survey (RGES) to discover bound exoplanets with semimajor axes greater than 1 au using gravitational microlensing. Roman will even be sensitive to planetary-mass objects that are not gravitationally bound to any host star. Such free-floating planetary-mass objects (FFPs) will be detected as isolated microlensing events with timescales shorter than a few days. A measurement of the abundance and mass function of FFPs is a powerful diagnostic of the formation and evolution of planetary systems, as well as the physics of the formation of isolated objects via direct collapse. We show that Roman will be sensitive to FFP lenses that have masses from that of Mars (0.1 M {sub ⊕}) to gas giants (M ≳ 100 M {sub ⊕}) as isolated lensing events with timescales from a few hours to several tens of days, respectively. We investigate the impact of the detection criteria on the survey, especially in the presence of finite-source effects for low-mass lenses. The number of detections will depend on the abundance of such FFPs as a function of mass, which is at present poorly constrained. Assuming that FFPs follow the fiducial mass function of cold, bound planets adapted from Cassan et al., we estimate that Roman will detect ∼250 FFPs with masses down to that of Mars (including ∼60 with masses ≤ M {sub ⊕}). We also predict that Roman will improve the upper limits on FFP populations by at least an order of magnitude compared to currently existing constraints.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

A Warm Jupiter Transiting an M Dwarf: A TESS Single-transit Event Confirmed with the Habitable-zone Planet Finder

We confirm the planetary nature of a warm Jupiter transiting the early M dwarf TOI-1899 using a combination of available TESS photometry; high-precision, near-infrared spectroscopy with the Habitable-zone Planet Finder; and speckle and adaptive optics imaging. The data reveal a transiting companion on an ∼29 day orbit with a mass and radius of 0.66±0.07 M{sub J} and 1.15{sub −0.05}{sup +0.04} R{sub J}, respectively. The star, TOI-1899, is the lowest-mass star known to host a transiting warm Jupiter, and we discuss the follow-up opportunities afforded by a warm (T{sub eq}∼362 K) gas giant orbiting an M0 star. Our observations reveal that TOI-1899.01 is a puffy warm Jupiter, and we suggest additional transit observations to both refine the orbit and constrain the true dilution observed in TESS.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Evidence that the Hot Jupiter WASP-77 A b Formed Beyond Its Parent Protoplanetary Disk’s H2O Ice Line

Idealized protoplanetary disk and giant planet formation models have been interpreted to suggest that a giant planet's atmospheric abundances can be used to infer its formation location in its parent protoplanetary disk. It has recently been reported that the hot Jupiter WASP-77 A b has subsolar atmospheric carbon and oxygen abundances with a solar C/O abundance ratio. Assuming solar carbon and oxygen abundances for its host star WASP-77 A, WASP-77 A b's atmospheric carbon and oxygen abundances possibly indicate that it accreted its envelope interior to its parent protoplanetary disk's H 2 O ice line from carbon-depleted gas with little subsequent planetesimal accretion or core erosion. We show that the photospheric abundances of carbon and oxygen in WASP-77 A are supersolar with a subsolar C/O abundance ratio, implying that WASP-77 A b's atmosphere has significantly substellar carbon and oxygen abundances with a superstellar C/O ratio. Our result possibly indicates that WASP-77 A b's envelope was accreted by the planet beyond its parent protoplanetary disk's H 2 O ice line. While numerous theoretical complications to these idealized models have now been identified, the possibility of nonsolar protoplanetary disk abundance ratios confound even the most sophisticated protoplanetary disk and giant planet formation models. We therefore argue that giant planet atmospheric abundance ratios can only be meaningfully interpreted relative to the possibly nonsolar mean compositions of their parent protoplanetary disks as recorded in the photospheric abundances of their dwarf host stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Keck/NIRSPEC Studies of He ι in the Atmospheres of Two Inflated Hot Gas Giants Orbiting K Dwarfs: WASP-52b and WASP-177b

We present the detection of neutral helium at 10833 Å in the atmosphere of WASP-52b and tentative evidence of helium in the atmosphere of the grazing WASP-177b, using high-resolution observations acquired with the NIRSPEC instrument on the Keck II telescope. We detect excess absorption by helium in WASP-52b's atmosphere of 3.44% ± 0.31% (11σ), or equivalently 66 ± 5 atmospheric scale heights. This absorption is centered on the planet's rest frame (Δv = 0.00 ± 1.19 km s –1 ). We model the planet's escape using a 1D Parker wind model and calculate its mass-loss rate to be ~1.4 × 10 11 g s –1 , or equivalently 0.5% of its mass per gigayear. For WASP-177b, we see evidence for redshifted (Δv = 6.02 ± 1.88 km s –1 ) helium-like absorption of 1.28% ± 0.29% (equal to 23 ± 5 atmospheric scale heights). However, due to residual systematics in the transmission spectrum of similar amplitude, we do not interpret this as significant evidence for He absorption in the planet's atmosphere. Using a 1D Parker wind model, we set a 3σ upper limit on WASP-177b's escape rate of 7.9 × 10 10 g s –1 . Our results, taken together with recent literature detections, suggest the tentative relation between XUV irradiation and He ι absorption amplitude may be shallower than previously suggested. Our results highlight how metastable helium can advance our understanding of atmospheric loss and its role in shaping the exoplanet population.

79 ASTRONOMY AND ASTROPHYSICS↗