The compositions of the HR 8799 planets reflect accretion of both solids and metal-enriched gas

Abstract

With four giant planets ($m\sim 5-10M_{\mathrm{Jup}}$, $T_\rm{eff}\sim900-1200$ K) orbiting between 15-70 au, HR 8799 provides an unparalleled testbed for studying giant planet formation and probing compositional trends across the protoplanetary disk. We present new JWST/NIRSpec IFU observations ($2.85-5.3\mu$m, $R\approx 2700$) that now include the spectrum of HR 8799 b, and higher S/N spectra for HR 8799 c, d, and e compared to that in Ruffio & Xuan et al. We detect CO, CH${}_4$, H${}_2$O, H${}_2$S, CO${}_2$, and for planet b, NH${}_3$. We combine the NIRSpec spectra with $1-5\mu$m photometry to perform atmospheric retrievals that account for disequilibrium chemistry and clouds, and allow C/H, O/H, N/H, and S/H to scale independently. While the four planets are similarly enriched in carbon and oxygen, with C/H and O/H between $3-5\times$ stellar, we observe a tentative trend of increasing S/H - a tracer of refractory solids - from $2-5\times$ stellar with increasing orbital distance. From HR 8799 b's NH${}_3$ abundance, we estimate $N/H=21.2_{-8.8}^{+16.2}\times$ stellar, suggesting the outer planet accreted significant amounts of N-rich gas. Overall, the elemental abundance patterns we observe are consistent with a picture where planet b formed between the CO snowline and the more-distant N${}_2$ snowline, while the inner planets accreted $3\times$ stellar CO-enriched disk gas within the CO snowline. The excess volatile mass from pebble drift and evaporation implies an integrated pebble flux of $750\pm 200M_{\oplus }$. The increase in the planets' S/H with orbital distance implies more solid accretion further out, which is quantitatively compatible with expectations from both pebble and planetesimal accretion ($2\times$ Minimum Mass Solar Nebula) paradigms.

Published in ApJ. The planet spectra are available in Zenodo at https://doi.org/10.5281/zenodo.19355669

References in corpus (92)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
• Detection of Carbon Monoxide and Water Absorption Lines in an Exoplanet Atmosphere
• The imprint of exoplanet formation history on observable present-day spectra of hot Jupiters
• An Ice Age JWST inventory of dense molecular cloud ices
• The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. A Statistical Characterization of Class 0 and I Protostellar Disks
• A new set of atmosphere and evolution models for cool T-Y brown dwarfs and giant exoplanets
• Photochemically-produced SO${}_2$ in the atmosphere of WASP-39b
• Astrochemistry and compositions of planetary systems
• ExoMol molecular line lists XXXV: a rotation-vibration line list for hot ammonia
• Chemical enrichment of giant planets and discs due to pebble drift
• ExoMol molecular line lists - XVI: The rotation-vibration spectrum of hot H${}_2$S
• An accurate, extensive, and practical line list of methane for the HITEMP database
• Methane, Carbon Monoxide, and Ammonia in Brown Dwarfs and Self-Luminous Giant Planets
• Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e
• VULCAN: an Open-Source, Validated Chemical Kinetics Python Code for Exoplanetary Atmospheres
• One Solution to the Mass Budget Problem for Planet Formation: Optically Thick Disks with Dust Scattering
• Dust masses of young disks: constraining the initial solid reservoir for planet formation
• Tracing the formation history of giant planets in protoplanetary disks with Carbon, Oxygen, Nitrogen and Sulphur
• Simultaneous Detection of Water, Methane and Carbon Monoxide in the Atmosphere of Exoplanet HR8799b
• Setting the volatile composition of (exo)planet-building material. Does chemical evolution in disk midplanes matter?
• Ammonium salts are a reservoir of nitrogen on a cometary nucleus and possibly on some asteroids
• How drifting and evaporating pebbles shape giant planets I: Heavy element content and atmospheric C/O
• The water abundance in Jupiter's equatorial zone
• Abundances in the Local Region II: F, G and K Dwarfs and Subgiants
• New study of the line profiles of sodium perturbed by H2
• Planet-forming material in a protoplanetary disc: the interplay between chemical evolution and pebble drift
• Dust growth and evolution in protoplanetary disks
• Abundant refractory sulfur in protoplanetary disks
• Jupiter's composition suggests its core assembled exterior to the N2 snowline
• The 13O-rich atmosphere of a young accreting super-Jupiter
• Improving and Assessing Planet Sensitivity of the GPI Exoplanet Survey with a Forward Model Matched Filter
• Excess C/O and C/H in outer protoplanetary disk gas
• A New Window into Planet Formation and Migration: Refractory-to-Volatile Elemental Ratios in Ultra-hot Jupiters
• Including Dust Coagulation in Hydrodynamic Models of Protoplanetary Disks: Dust Evolution in the Vicinity of a Jupiter-mass Planet
• How drifting and evaporating pebbles shape giant planets II: Volatiles and refractories in atmospheres
• Chemical Diversity in Protoplanetary Disks and Its Impact on the Formation History of Giant Planets
• Breaking Degeneracies in Formation Histories by Measuring Refractory Content in Gas Giants
• A Clear View of a Cloudy Brown Dwarf Companion from High-Resolution Spectroscopy
• Deep Thermal Infrared Imaging of HR 8799 bcde: New Atmospheric Constraints and Limits on a Fifth Planet
• Retrieval survey of metals in six ultra-hot Jupiters: Trends in chemistry, rain-out, ionisation and atmospheric dynamics
• Leaky dust traps: How fragmentation impacts dust filtering by planets
• The Role of Ice Compositions for Snowlines and the C/N/O Ratios in Active Disks
• Probing the Extent of Vertical Mixing in Brown Dwarf Atmospheres with Disequilibrium Chemistry
• Deep exploration of the planets HR 8799 b, c, and d with moderate resolution spectroscopy
• Jupiter formed as a pebble pile around the N${}_2$ ice line
• On the Composition of Young, Directly Imaged Giant Planets
• Assessing the C/O Ratio Formation Diagnostic: A Potential Trend with Companion Mass
• Abundant ammonium hydrosulphide embedded in cometary dust grains
• Volatile-to-sulfur Ratios Can Recover a Gas Giant's Accretion History
• Four-of-a-kind? Comprehensive atmospheric characterisation of the HR 8799 planets with VLTI/GRAVITY
• Empirically Determining Substellar Cloud Compositions in the era of JWST
• Quartz Clouds in the Dayside Atmosphere of the Quintessential Hot Jupiter HD 189733 b
• Jupiter's formation in the vicinity of the amorphous ice snowline
• A detailed characterization of HR 8799's debris disk with ALMA in Band 7
• CRIRES+ and ESPRESSO reveal an atmosphere enriched in volatiles relative to refractories on the ultra-hot Jupiter WASP-121b
• Retrieving C and O Abundance of HR 8799 c by Combining High- and Low-Resolution Data
• Orbital and dynamical analysis of the system around HR 8799. New astrometric epochs from VLT/SPHERE and LBT/LUCI
• An exact, generalised Laplace resonance in the HR 8799 planetary system
• 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
• The ESO SupJup Survey I: Chemical and isotopic characterisation of the late L-dwarf DENIS J0255-4700 with CRIRES${}^{+}$
• Jupiter's "Cold" Formation in the Protosolar Disk Shadow: An Explanation for the Planet's Uniformly Enriched Atmosphere
• Measuring the Dust Masses of Protoplanetary Disks in Lupus with ALMA: Evidence that Disks can be Optically Thick at 3 mm
• Imaging detection of the inner dust belt and the four exoplanets in the HR8799 system with JWST's MIRI coronagraph
• Testing a New Model of Embedded Protostellar Disks Against Observation: The Majority of Orion Class 0/I Disks Are Likely Warm, Massive, and Gravitationally Unstable
• Measuring Elemental Abundances of JWST Target Stars for Exoplanet Characterization I. FGK Stars
• Atmospheric Monitoring and Precise Spectroscopy of the HR 8799 Planets with SCExAO/CHARIS
• X-shooter spectroscopy of young stellar objects in Lupus: Lithium, iron, and barium elemental abundances
• JWST-TST High Contrast: Living on the Wedge, or, NIRCam Bar Coronagraphy Reveals CO${}_2$ in the HR 8799 and 51 Eri Exoplanets' Atmospheres
• Revising the Giant Planet Mass-Metallicity Relation: Deciphering the Formation Sequence of Giant Planets
• Deep orbital search for additional planets in the HR 8799 system
• Establishing Dust Rings and Forming Planets Within Them
• Evidence for SiO cloud nucleation in the rogue planet PSO J318
• The Sonora Substellar Atmosphere Models. V: A Correction to the Disequilibrium Abundance of CO${}_2$ for Sonora Elf Owl
• The centimeter emission from planet-forming disks in Taurus
• Atmospheric characterization of the super-Jupiter HIP 99770 b with KPIC
• The JWST Weather Report: retrieving temperature variations, auroral heating, and static cloud coverage on SIMP-0136
• Three-dimensional transport of solids in a protoplanetary disk containing a growing giant planet
• Jupiter-like uniform metal enrichment in a system of multiple giant exoplanets
• MIRI-LRS spectrum of a cold exoplanet around a white dwarf: water, ammonia, and methane measurements
• Enriched volatiles and refractories but deficient titanium on the dayside atmosphere of WASP-121b revealed by JWST/NIRISS
• Refractory and Volatile Species in the UV-to-IR Transmission Spectrum of Ultra-hot Jupiter WASP-178b with HST and JWST
• A High-Resolution Spectroscopic Survey of Directly Imaged Companion Hosts: I. Determination of diagnostic stellar abundances for planet formation and composition
• PDS 70b Shows Stellar-like Carbon-to-oxygen Ratio
• Detailed Microwave Continuum Spectra from Bright Protoplanetary Disks in Taurus
• Strong NUV Refractory Absorption and Dissociated Water in the Hubble Transmission Spectrum of the Ultra Hot Jupiter KELT-20 b
• The Sonora Substellar Atmosphere Models VI. Red Diamondback: Extending Diamondback with SPHINX for Brown Dwarf Early Evolution
• Atmospheric abundances and bulk properties of the binary brown dwarf Gliese 229 Bab from JWST/MIRI spectroscopy
• Testing the accretion scenario of lambda Boo stars
• Abundance analysis of stars hosting gas-rich debris disks
• The HR 8799 Debris Disc: Shaped by Planetary Migration and a Possible Fifth Outermost Planet

Cited by in corpus (3)

• Direct Imaging Discovery of Giant Exoplanet $\beta$ Pictoris d: A Decade-Long Game of Hide-and-Seek
• JWST-TST High Contrast: First Direct Spectroscopy of GJ 504 b reveals Clouds and Possible Metal Enrichment
• JWST high-contrast spectroscopy with speckle modelling: Atmospheric retrievals of the T dwarf companion HD 19467 B