arXiv subjects

Jennifer B. Bergner

Publications and source records attributed to Jennifer B. Bergner.

At least 19 recordsLinked to original sources

arXiv2026

SMA Observations Reveal Abundant HNC Chemistry in Transition Disks

The physical and chemical conditions of protoplanetary disks shape the properties of nascent planetary systems. The line ratios and relative abundances of the HCN-HNC isomer pair are well-suited for tracing these gas conditions, since isomer chemistry is linked to the underlying temperature, elemental abundances, and irradiation environment of the emitting gas. While HCN emits bright lines regularly observed in disks, the fainter HNC lines are targeted significantly less often, precluding our ability to calibrate the HNC-to-HCN ratio as a tracer of disk properties. Here, we present new Submillimeter Array observations of five transition disks around the T Tauri stars GM Aur, J1604, LkCa 15, GG Tau, and V4046 Sgr, covering the J=3-2 and J=4-3 lines of HCN and HNC. We detected at least one line of both HCN and HNC in each source and measured disk-integrated HNC-to-HCN flux and column density ratios of $\approx$0.1-0.7 and 0.1-0.4, respectively. For all sources, measured HNC fluxes exceed predictions from models of full (non-transition) disks by $\approx$3-10x, while HCN fluxes appear typical. The relative brightness of HNC vs. HCN in transition disks strongly suggests a link between the presence of a cavity and efficient HNC production. We corroborate this trend using chemical models of the DM Tau transition disk, showing HNC production and destruction are connected to the radiation environment. In our sample, disk-integrated HNC-to-HCN column density ratio shows no trend with disk gas temperature but positively correlates with disk mass due to increased HNC abundance in the larger reservoirs of cooler gas in more massive disks.

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arXiv2026

Using Scattered Near-Infrared Light to Map Water Ice in Prestellar Cores with SPHEREx

We present the first coreshine-derived, spatially-resolved maps of the 3 $\mu$m H$_2$O ice absorption feature in four prestellar cores, using SPHEREx spectra. Ices are a key component of dense cores in molecular clouds, playing a central role in the chemistry of planet formation around young stars. However, spatially resolved abundance studies remain limited, typically relying on unevenly distributed background star sightlines. Here, we take advantage of the all-sky spectrophotometric capabilities of SPHEREx to construct ice absorption maps with uniform spatial resolution using the illumination of dense cores by scattered Galactic radiation, or coreshine. To demonstrate proof of concept, we analyse the spatially varying H$_2$O ice absorption in four nearby (~140 pc) prestellar cores - L1544, CrA 151, L260 and L1512. Two cores follow the expected spatial trend of ice absorption peaking at the centre, but the two densest cores show a surprising drop in observed ice absorption in the innermost regions. To interpret the absorption maps, we construct analytical and simulated models of a Bonnor-Ebert sphere illuminated by scattering. We study the effects of different geometric configurations, ice mass fractions, and spatial differences in ice composition. None of these can explain the reduced central absorption, pointing to an unexplained physical or chemical effect operating in the densest prestellar regions. Our simulations further show that spectra derived from coreshine provide a robust tracer of spatially varying ice density and composition, establishing SPHEREx scattered-light spectroscopy as a powerful new probe of ice in dense cores.

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arXiv2026

JWST Edge-on Disk Ice (JEDIce): Vibrationally hot, rotationally cold H$_2$ in the outer disk of Oph 163131 non-thermally excited by UV and cosmic rays

Constraining ionization and excitation processes in protoplanetary disks is essential for understanding the chemical structure and evolution of disk material, shaping planet formation pathways. We present JWST/NIRSpec IFU observations of the edge-on disk Oph 163131, which reveal a unusual ro-vibrational H$_2$ spectrum dominated by the 1--0 O(2) line (2.627 $\mu$m), with suppressed higher-$J$ emission despite excitation to $v=2$ and $3$. This vibrationally hot, rotationally cold H$_2$ emission is spatially extended, broadly following the molecular disk traced by CO($J{=}2$--1), with emission increasing above and below a thin midplane dark lane and extending radially beyond $\sim$200 au, where near-IR scattered-light emission is no longer dominant. We interpret the observed H$_2$ emission as arising from non-thermal excitation in cold, dense outer-disk gas, where collisions depopulate higher-$J$ rotational levels within each vibrational manifold prior to emission, producing the characteristic ``$v$-hot, $J$-cold" spectrum. We consider both ultraviolet irradiation and cosmic-ray excitation as contributors to the H$_2$ emission and find that their combined action, together with collisional de-excitation of high-$J$ level populations, broadly reproduces the observed line ratios and morphology. Within this framework, we infer a rather high effective cosmic-ray ionization rate of $\sim(1$-$10)\times10^{-15}$ s$^{-1}$ in the presence of a moderate UV field ($\chi_{UV}=100-1000$, in Draine units). These results for disks, together with the recent findings by Bialy et al. 2025 for the lower-density starless core B68, highlight the potential of ro-vibrational H$_2$ emission as a novel probe of cosmic-ray ionization.

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arXiv2026

CORINOS V: Radiative transfer effects in protostellar ice observations

Recent observations of protostars with the James Webb Space Telescope have revealed unprecedented chemical complexity from their ice absorption features. However, these spectra are likely influenced by radiative transfer effects, and there is little understanding of how this impacts our ability to identify, quantify, and interpret the observed ice features. We have developed a new modeling framework to investigate the radiative transfer through icy protostellar envelopes, and apply this to the IRAS 15398-3359 protostar observed by the JWST CORINOS program. The modeled H$_2$O and CO column densities are similar to previous empirical studies, but we require a high CO$_2$/H$_2$O ratio of 76% to match the optical depth of the 15 $\mu$m band. We use our modeled continuum to calculate a 6-10 $\mu$m optical depth spectrum, and see considerable differences compared to a simple polynomial continuum model, underscoring the challenges with quantifying trace ice species in this range. For this source, we find that the observed absorption predominantly originates along the viewing line of sight between 1000 - 2000 au, peaking at the transition from the outflow cavity to the envelope; the spectra are largely insensitive to absorption from ices in the outer envelope, which extends out to 20,000 au. Lastly, we show that depending on how the line of sight intersects the cavity, the apparent CO$_2$/H$_2$O and CO/H$_2$O column density ratios can be underestimated compared to the underlying ice abundance ratios. Together this provides important context for interpreting the ice constraints derived from JWST observations of protostars.

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arXiv2026

JWST Edge-on Disk Ice (JEDIce): Program overview and ice survey results

The icy material within protoplanetary disks plays a central role in planet formation, yet remains poorly characterized by observations. We present 1.6-28$\mu$m spectra of five disks obtained as part of the JWST Edge-on Disk Ice (JEDIce) program, representing the largest survey of disk ices to date. The major ice species H$_2$O, CO$_2$, and CO are detected towards all disks, and exhibit a wide range of absolute optical depths and optical depth ratios across the sample. This is suggestive of a range of ice abundances and compositions, but quantitative constraints will require radiative transfer modeling. All disks exhibit ice features across the entire spatial region where the IR continuum is detected; vertically elevated ice grains therefore seem to be ubiquitous in disks. The CO ice is consistently dominated by apolar CO:CO$_2$ mixtures, implying that the disk ice compositions are neither completely reset nor pristinely inherited from the protostellar stage. The presence of these mixtures also suggests that entrapment may be important in shaping the spatial distribution of CO within the disks. Small molecules commonly seen in protostellar ices (CH$_4$, CH$_3$OH, NH$_3$) are generally not detected in our sample, though tracers of ammonium salts (OCN$^-$ and the 6.85 $\mu$m band) are common, potentially reflecting an evolution towards comet-like ice compositions. The spectra also contain a wealth of information about the micron-sized dust, atomic and molecular gas, and PAH content, which together with the ice constraints will provide a comprehensive picture of the chemical, physical, and dynamical state of these systems.

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arXiv2026

Water D/H in 3I/ATLAS as a Probe of Formation Conditions in Another Planetary System

Water reservoirs in the Solar System exhibit a deuterium enrichment that links back to the physical environment at the time of stellar birth. Gas-phase and ice-grain deuterium enrichments occur through chemical processes that operate at low temperatures ($<$~30~K) pointing towards an origin in the prestellar molecular cloud or in the outer parts of the protoplanetary disk. However, not all stars are born in environments similar to our Sun, nor do their subsequent evolutionary histories follow the same path. These environmental differences can be traced by the water deuterium-to-hydrogen (D/H) ratio. Here we use ALMA observations of the interstellar comet 3I/ATLAS to constrain the water D/H ratio in extrasolar cometary material. With a water D/H value of [D/H]$_{\mathrm{H_2O}} > 6.6\times10^{-3}$, 3I/ATLAS shows a deuterium enrichment exceeding Earth's ocean value by more than a factor of $\gtrsim40$ and typical Solar System cometary values by more than a factor of $\gtrsim30$. The elevated deuterium enrichment points to water that formed under colder, less irradiated conditions and from less thermally processed material, consistent with an origin in a planetary system that formed under different physical and chemical conditions than our own.

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arXiv2025

CORINOS IV: Quantifying Baseline-Fitting Uncertainties in SO$_2$ Ice Measurements with JWST/MIRI

Sulfur dioxide (SO$_2$) ice has been tentatively detected in protostellar envelopes, but its reliability as a solid-state sulfur reservoir remains unclear. We present new measurements of SO$_2$ ice from 6.8-8.5 $\mu$m toward four Class 0 protostars observed with JWST's Mid-Infrared (MIRI) Medium Resolution Spectrometer, as part of the COMs ORigin Investigated by the Next-generation Observatory in Space (CORINOS) program. The sample spans a luminosity range from 1 $L_\odot$ (B335, IRAS 15398-3359) to 10 $L_\odot$ (L483, Ser-emb~7). To assess continuum placement uncertainty in absorption spectra, we apply randomized polynomial fits over the restricted region. We fit laboratory spectra from the Leiden Ice Database for Astrochemistry (LIDA) using the open-source Python library Omnifit. We detect the 7.7 $\mu$m CH$_4$ band in all sources and find its column density robust to baseline choice, providing a reference for evaluating the weaker SO$_2$ feature on its blue shoulder and quantifying baseline-related uncertainty. Three SO$_2$ laboratory ices were tested: pure SO$_2$ ice yields 0.3-1.2% of volatile sulfur may be locked in SO$_2$ ice (lower and upper limits); CH$_3$OH:SO$_2$ ice gives 0.02-0.18%, but with lower quality fitting. The best-fitting H$_2$O:SO$_2$ ice yields 0.2-0.9%, which we consider the most realistic. These ranges define plausible bounds on SO$_2$ ice abundances in our sample. We find evidence for SO$_2$ in Ser-emb 7, L483, and IRAS 15398-3359, but emphasize the noisy spectrum of B335 prevents a definitive detection. Comparing SO$_2$ ice abundances across the different environments, we assess how conditions influence role of SO$_2$ as a potential sulfur reservoir and implications for the longstanding ``missing sulfur'' problem.

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arXiv2025

The Flying Saucer edge-on disc's Near Infrared silhouette revealed by the JWST JEDIce program

Edge-on discs offer a unique opportunity to probe radial and vertical dust and gas distributions in the protoplanetary phase. This study aims to investigate the distribution of micron-sized dust particles in the Flying Saucer (BKLT J162813-243139) in Rho Ophiuchi, leveraging the unique observational conditions of a bright infrared background that enables the edge-on disc to be seen in both silhouette and scattered light at certain, specific wavelengths. As part of the JWST Edge-on Disc Ice program ('JEDIce'), we use NIRSpec IFU observations of the Flying Saucer, serendipitously observed against a PAH-emitting background, to constrain the dust distribution and grain sizes through radiative transfer modelling. Observation of the Flying Saucer in silhouette at 3.29 microns reveals that the midplane radial extent of small dust grains is ~235 au, larger than the large-grain disc extent previously determined to be 190 au from millimetre data. The scattered light observed in emission probes micron sized icy grains at large vertical distances above the midplane. The vertical extent of the disc silhouette is similar at visible, near-IR, and mid-IR wavelengths, corroborating the conclusion that dust settling is inefficient for grains as large as tens of microns, vertically and radially.

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arXiv2025

Variation of the disk thickness across ice bands: A method to determine ice abundances in highly inclined protoplanetary disks

The James Webb Space Telescope provides unprecedented information to study ices in protoplanetary disks. However, the saturation of ice bands in highly inclined disks hinders the measurement of ice abundances using classical spectroscopy. This is unfortunate as the presence and more importantly abundance of ices plays a key role in, e.g., the evolution of dust (because it modifies the sticking properties) and the composition of planetesimals and exoplanetary atmospheres. To overcome this issue and quantify the ice abundance within disks, we introduce a new method based on measuring the changes in the apparent disk thickness as a function of wavelength, which is directly and quantitatively related to the grain opacity. Specifically, we expect i) that the increased opacity within ice bands should result in a thicker disk than in the adjacent continuum, and ii) the thickness variations to be proportional to the abundance of ice. We extracted the disk thickness in model images of edge-on disks containing different abundances of water ice, as well as in James Webb Space Telescope spectral imaging of four edge-on disks. For both models and observations, the disk thickness decreases toward longer wavelengths except across the positions of ice absorption features where the thickness is enhanced across the band. In the model images, we demonstrate that this effect increases with ice abundance without any hint of saturation. This definitely demonstrates the presence of the ice species within each disk and confirms our expectation that this method can be applied to estimate ice abundances. Thanks to this method, it will thus be possible to constrain the ice abundance in highly inclined disks with disks model fitting. Unlike spectroscopic analysis, this method is not subject to saturation and should therefore be more robust and applicable to all disks for which the two surfaces can be resolved.

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arXiv2025

PEACHES IV: Tracing the Formation & Evolution of C$_2$H in Perseus Low-Mass Protostars

The radical hydrocarbon molecule C$_2$H is widely detected in various stages of star and planet formation, and has emerged as a useful tracer of high-C/O gas within the photochemically active surface layers of mature (Class II) protoplanetary disks. However, the chemistry and evolution of C$_2$H within younger (Class 0/I) protostars remains much more poorly understood. Here, using data observed as part of the PEACHES survey along with new ALMA ACA observations, we investigate the C$_2$H emission towards an unbiased sample of 35 Class 0/I low-mass protostars in Perseus. With this large sample, we identify a clear association between C$_2$H emission and the protostellar outflow cavity walls, and a consistent spatial anti-correlation between C$_2$H and SO emission. Together, these trends confirm that C$_2$H is tracing photochemically active, O-poor gas in these younger sources. We fitted the C$_2$H spectra with a simple LTE model to yield column density maps, and find values ranging from 10$^{14}$ -- 10$^{15}$ cm$^{-2}$ in these sources. We also looked for trends in the C$_2$H emission morphology as a function of various protostellar evolutionary metrics, but find no clear patterns: the C$_2$H emission remains spatially extended in most sources, independent of age. This indicates that the transition to the compact C$_2$H emission observed on the surface of Class II disks must happen rapidly, sometime just after the embedded stage.

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arXiv2025

On Linking Planet Formation Models, Protoplanetary Disk Properties, and Mature Gas Giant Exoplanet Atmospheres

Measuring a single elemental ratio (e.g., carbon-to-oxygen) provides insufficient information for understanding the formation mechanisms and evolution that affect our observations of gas giant planet atmospheres. Although the fields of planet formation, protoplanetary disks, and exoplanets are well established and interconnected, our understanding of how to self-consistently and accurately link the theoretical and observational aspects of these fields together is lacking. To foster interdisciplinary conversations, the Max-Planck Institut für Astronomie (MPIA) hosted a week-long workshop called, "Challenge Accepted: Linking Planet Formation with Present-Day Atmospheres." Here, we summarize the latest theories and results in planet formation modeling, protoplanetary disk observations, and atmospheric observations of gas giant atmospheres to address one of the challenges of hosting interdisciplinary conferences: ensuring everyone is aware of the state-of-the-art results and technical language from each discipline represented. Additionally, we highlight key discussions held at the workshop. Our main conclusion is that it is unclear what the ideal observable is to make this link between formation scenarios and exoplanet atmospheres, whether it be multiple elemental abundance ratios, measuring refractory budgets, or something else. Based on discussions held throughout the workshop, we provide several key takeaways of what the workshop attendees feel need the most improvement and exploration within each discipline.

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arXiv2025

Refractory phosphorus in the HD 100546 protoplanetary disk

The phosphorus budget of planets is intertwined with their formation history and is thought to influence their habitability. The chemical reservoirs and volatile \emph{vs} refractory budget of phosphorus in planet-forming environments have so far eluded empirical characterisation. We employ high-resolution spectra from HST/STIS in the ultraviolet and APEX in the sub-mm to constrain the phosphorus budget in the well-characterized HD\,100546 star and protoplanetary disk system. We measure $\log{(P/H)_{\star}}=-7.50^{+0.23}_{-0.28}$ on the stellar surface, which traces the total inventory of P in accreting gas \emph{and }dust from the inner disk. The inner disk gas, inside of the main dust trap, has $\log{(P/H)_{\rm in}}\lesssim-8.70$, and the outer disk gas $\log{(P/H)_{\rm out}}\lesssim-9.30$. Phosphorus in the disk is carried by a relatively refractory reservoir, consistent with minerals such as apatite or schreibersite, or with ammonium phosphate salts, in terms of sublimation temperature. We discuss the impact this might have on the two protoplanets around HD\,100546. Our results contribute to our understanding of the chemical habitability of planetary systems and lay a foundation for future explorations, especially in the context of JWST and \emph{Ariel} which can study phosphorus in exoplanet atmospheres.

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arXiv2025

H2S ice sublimation dynamics: experimentally constrained binding energies, entrapment efficiencies, and snowlines

Hydrogen sulfide (H2S) is thought to be an important sulfur reservoir in interstellar ices. It serves as a key precursor to complex sulfur-bearing organics, and has been proposed to play a significant role in the origin of life. Although models and observations both suggest H2S to be present in ices in non-negligible amounts, its sublimation dynamics remain poorly constrained. In this work, we present a comprehensive experimental characterization of the sublimation behavior of H2S ice under astrophysically-relevant conditions. The sublimation behavior of H2S was monitored with a quadrupole mass spectrometer (QMS) during temperature-programmed desorption (TPD) experiments. These experiments are used to determine binding energies and entrapment efficiencies of H2S, which are then employed to estimate its snowline positions in a protoplanetary disk midplane. We derive mean binding energies of 3159\pm46 K for pure H2S ice and 3392\pm56 K for submonolayer H2S desorbing from a compact amorphous solid water (cASW) surface. These values correspond to sublimation temperatures of around 64 K and 69 K in the disk midplane, placing its sublimation fronts at radii just interior to the CO2 snowline. We also investigate the entrapment of H2S in water ice and find it to be highly efficient, with ~75-85% of H2S remaining trapped past its sublimation temperature for H2O:H2S mixing ratios of ~5-17:1. We discuss potential mechanisms behind this efficient entrapment. Our findings imply that, in protoplanetary disks, H2S will mostly be retained in the ice phase until water crystallizes, at radii near the water snowline, if it forms mixed into water ice. This has significant implications for the possibility of H2S being incorporated into icy planetesimals and its potential delivery to terrestrial planets, which we discuss in detail.

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arXiv2025

A deep search for Complex Organic Molecules toward the protoplanetary disk of V883 Ori

Complex Organic Molecules (COMs) in the form of prebiotic molecules are potentially building blocks of life. Using Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 observations in spectral scanning mode, we carried out a deep search for COMs within the disk of V883 Ori, covering frequency ranges of $\sim$ 348 - 366 GHz. V883 Ori is an FUor object currently undergoing an accretion burst, which increases its luminosity and consequently increases the temperature of the surrounding protoplanetary disk, facilitating the detection of COMs in the gas phase. We identified 26 molecules, including 14 COMs and 12 other molecules, with first detection in this source of the molecules: CH3OD, H2C17O, and H213CO. We searched for multiple nitrogen-bearing COMs, as CH3CN had been the only nitrogen-bearing COM that has been identified so far in this source. We also detected CH3CN, and tentatively detect CH3CH2CN, CH2CHCN, CH3OCN, CH3NCO, and NH2CHO. We compared the abundances relative to CH3OH with those in the handful of objects with previous detections of these species: the Class 0 protostars IRAS 16293-2422 A, IRAS 16293-2422 B and B1-c, the high-mass star-forming region Sagittarius B2 (North), the Solar System comet 67P/Churyumov-Gerasimenko, and the protoplanetary disk of Oph-IRS 48. We report $\sim$ 1 to 3 orders of magnitude higher abundances compared to Class 0 protostars and $\sim$ 1 to 3 orders of magnitude lower abundances compared to the protoplanetary disk, Sagittarius B2 (North), and 67P/C-G. These results indicate that the protoplanetary disk phase could contribute to build up of COMs.

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arXiv2024

Protoplanetary disk chemistry and structure

Knowledge of the composition of material that will form planets is crucial to understand planetary diversity and the occurrence of potentially habitable planets. Ultimately, it is the chemistry in circumstellar disks that determines the global make up of planetary systems, as the dust in these disks grows into giant planet cores and rocky planets, the gas becomes incorporated in giant planet atmospheres, and the ices can be delivered to rocky planets by comets and meteorites. With the advent of ALMA a decade ago and the recent launch of JWST, the composition of the disk gas and ice can now be studied in great detail. This review will provide an overview of our current knowledge of the disk chemical structure, focusing on the six elements essential to life on Earth: carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P) and sulfur (S).

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arXiv2024

JWST ice band profiles reveal mixed ice compositions in the HH 48 NE disk

Planet formation is strongly influenced by the composition and distribution of volatiles within protoplanetary disks. With JWST, it is now possible to obtain direct observational constraints on disk ices, as recently demonstrated by the detection of ice absorption features towards the edge-on HH 48 NE disk as part of the Ice Age Early Release Science program. Here, we introduce a new radiative transfer modeling framework designed to retrieve the composition and mixing status of disk ices using their band profiles, and apply it to interpret the H2O, CO2, and CO ice bands observed towards the HH 48 NE disk. We show that the ices are largely present as mixtures, with strong evidence for CO trapping in both H2O and CO2 ice. The HH 48 NE disk ice composition (pure vs. polar vs. apolar fractions) is markedly different from earlier protostellar stages, implying thermal and/or chemical reprocessing during the formation or evolution of the disk. We infer low ice-phase C/O ratios around 0.1 throughout the disk, and also demonstrate that the mixing and entrapment of disk ices can dramatically affect the radial dependence of the C/O ratio. It is therefore imperative that realistic disk ice compositions are considered when comparing planetary compositions with potential formation scenarios, which will fortunately be possible for an increasing number of disks with JWST.

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arXiv2024

CORINOS II. JWST-MIRI detection of warm molecular gas from an embedded, disk-bearing protostar

We present James Webb Space Telescope (JWST) Mid-InfraRed Instrument (MIRI) observations of warm CO and H$_2$O gas in emission toward the low-mass protostar IRAS 15398-3359, observed as part of the CORINOS program. The CO is detected via the rovibrational fundamental band and hot band near 5 $μ$m, whereas the H$_2$O is detected in the rovibrational bending mode at 6-8 $μ$m. Rotational analysis indicates that the CO originates in a hot reservoir of $1598\pm118$ K, while the water is much cooler at $204\pm 7$ K. Neither the CO nor the H$_2$O line images are significantly spatially extended, constraining the emission to within $\sim$40 au of the protostar. The compactness and high temperature of the CO are consistent with an origin in the embedded protostellar disk, or a compact disk wind. In contrast, the water must arise from a cooler region and requires a larger emitting area (compared to CO) to produce the observed fluxes. The water may arise from a more extended part of the disk, or from the inner portion of the outflow cavity. Thus, the origin of the molecular emission observed with JWST remains ambiguous. Better constraints on the overall extinction, comparison with realistic disk models, and future kinematically-resolved observations may all help to pinpoint the true emitting reservoirs.

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arXiv2024

JWST-MIRI Spectroscopy of Warm Molecular Emission and Variability in the AS 209 Disk

We present MIRI MRS observations of the large, multi-gapped protoplanetary disk around the T-Tauri star AS 209. The observations reveal hundreds of water vapor lines from 4.9 to 25.5 $μ$m towards the inner $\sim1$ au in the disk, including the first detection of ro-vibrational water emission in this disk. The spectrum is dominated by hot ($\sim800$ K) water vapor and OH gas, with only marginal detections of CO$_2$, HCN, and a possible colder water vapor component. Using slab models with a detailed treatment of opacities and line overlap, we retrieve the column density, emitting area, and excitation temperature of water vapor and OH, and provide upper limits for the observable mass of other molecules. Compared to MIRI spectra of other T-Tauri disks, the inner disk of AS 209 does not appear to be atypically depleted in CO$_2$ nor HCN. Based on \textit{Spitzer IRS} observations, we further find evidence for molecular emission variability over a 10-year baseline. Water, OH, and CO$_2$ line luminosities have decreased by factors 2-4 in the new MIRI epoch, yet there are minimal continuum emission variations. The origin of this variability is yet to be understood.

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