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Carbon dioxide (CO2) is one of the most abundant ices in the solar system. It has been detected in giant planet atmospheres and on their moons, on and around comets, and even in regions of Mercury, the Moon, and Mars. However, despite their formation in the coldest regions of the protoplanetary disk, CO2 was not previously detected on trans-Neptunian objects (TNOs). Carbon monoxide (CO) was only expected to be present in the largest TNOs. Out of 45 total, we report the detection of both CO2 and CO in 42 and 24 TNOs, respectively, observed with the NIRSpec instrument on the JWST by the DiSCo-TNOs project (PID 2418). Our analysis shows that \diox is widespread in the trans-Neptunian region, independent of dynamical class, while CO is a common constituent of the reddest objects in our sample. The abundance and characteristics of \diox suggest that most of it could be primordially accreted. While, CO is probably being produced by ion irradiation of CO2 and other C-bearing species. Our results suggest the prevalence of two compositional groups among TNOs based on the abundance and properties of CO2 and CO. We discuss the implication of these results in the context of solar system formation.

The various dynamical classes in the trans-Neptunian region record the history of Neptune’s migration early in solar system history. The low-inclination, low-eccentricity cold classical objects are thought to be the remnants of the outer primordial disk of minor bodies, left undisturbed by the migration of Neptune, while all other classes were implanted on their current orbits from smaller heliocentric distances through interaction with Neptune. Many other trans-Neptunian objects (TNOs) were lost from the solar system entirely or transferred onto crossing orbits that resulted in collisions. Not unexpectedly, two very different populations of TNO binary systems are observed: (1) large TNOs with small satellites on relatively tight orbits and (2) small TNOs, mostly cold classicals, with roughly equal-sized components and relatively large separations. This stark contrast points to two very different formation mechanisms—giant impacts and co-formation—and corresponding expectations for the compositions of the components. Giant impacts are more likely to result in different compositions for the primary and secondary, while co-formation implies similar compositions. Observations with the JWST NIRSpec IFU provide sufficient spatial resolution to resolve TNO binaries and sufficient sensitivity to obtain spectra of both components. We have examined data for both large and small TNO binaries from GTO and GO programs and present spectral comparisons of the primaries and secondaries. The results of this work have implications for the early dynamical history and collisional environment in our own outer solar system, with links to other planetary systems with observed debris disks.

Centaurs are small bodies orbiting between Jupiter and Neptune that were scattered inwards from their sources in the trans-Neptunian region, and which will eventually feed the JFC population. A small fraction of Centaurs display comet-like activity, of which the drivers and triggers are not well understood. The range of heliocentric distances where the active Centaurs have been observed, and their median lifetime in the region, suggest this activity is neither driven by water-ice sublimation, nor entirely by super-volatiles. Here we present a dynamical study of 55 active Centaurs and high-perihelion JFCs and compare their dynamical behaviors to those of more than 260 known inactive objects in the region. Our results show there is a common feature present in the orbital evolution of active bodies - a sudden rapid decrease in semi-major axis aligned with decrease in eccentricity, which typically occurred less than several hundred years in the past. This 'a-dip', is in most cases not correlated with a substantial change in perihelion distance, and with a few exceptions it is not present in the orbital history known inactive Centaurs. Our thermodynamical modeling suggests the sudden decrease in semi-major axis could act as a trigger for the cometary activity on Centaurs due to the rapid change of thermal environment. Moreover, the lag between the a-jump and some recently observed active Centaurs could be used to constraint the volatiles and processes driving the cometary activity beyond the orbit of Jupiter. We have identified fourteen Centaur candidates with no observed prior periods of activity for possible future outbursts based on their recent a-dips, which are similar in magnitude to those observed in other active Centaurs and distant JFCs. These objects should be targets of high interest for observational activity monitoring. Figure 1: Comparison of the a-dips observed in orbital history of several known active Centaurs (left) compared to (right) a-dips of the identified inactive Centaurs – possible candidates for future outbursts. The dotted lines on the right panel show typical fluctuation of semi-major axis in the vast majority of inactive Centaurs.

The discovery of trans-Neptunian objects (TNOs) marked an important milestone in the understanding of the outer Solar System. Due to their environmental conditions, these objects could preserve the most pristine materials that were present on the protoplanetary disk. Studies focused on understanding TNOs physical and dynamical properties can be used to probe planetary formation processes and the subsequent solar system dynamical evolution that followed the formation era.Nowadays, above 3,000 TNOs have been detected, including four large ones that receive the official designation of dwarf-planets. Analysis of TNOs revealed a compositionally and dynamically diverse population. However, despite all the progress in the last decades, much is still unknown about the composition of the TNOs.The recently launched James Webb Space Telescope (launched on December 25, 2021) will provide a powerful tool to investigate the TNOs surface composition, where all prior instrumentation has fallen short. The NIRSpec instrument onboard JWST will provide high-quality data that will surpass the quality of the data available by orders of magnitude. DiSCo-TNOs, lead by the Florida Space Institute, is the only large program approved by JWST for the study of the Solar System. With it, we aim to assess the relative ratio of water ice, complex organics, silicates, and volatiles on the surface of a large sample of TNOs. This information is vital to improving models of the formation of our Solar System and other planetary systems. In this talk we present the scope of the DiSCo program, and the tools that are being developed to extract the maximal information from the data. We pay special attention to the compositional modeling technique that uses an implementation of a nested sampling algorithm for Bayesian inference of the abundances and grain sizes distribution of the materials present on TNOs surfaces.

We present analyses of Spitzer observations of 29P/Schwassmann–Wachmann 1 using 16 μm IRS “blue” peak-up (PU) and 24 and 70 μm MIPS images obtained on UT 2003 November 23 and 24 that characterize the Centaur’s large-grain (10–100 μm) dust coma during a time of non-outbursting “quiescent” activity. Estimates of ϵ f ρ for each band (16 μm (2600 ± 43 cm), 24 μm (5800 ± 63 cm), and 70 μm (1800 ± 900 cm)) follow the trend between nucleus size versus ϵ f ρ that was observed for the WISE/NEOWISE comet ensemble. A coma model was used to derive a dust production rate in the range of 50–100 kg s−1. For the first time, a color temperature map of SW1's coma was constructed using the 16 and 24 μm imaging data. With peaks at ∼140 K, this map implies that coma water-ice grains should be slowly sublimating and producing water gas in the coma. We analyzed the persistent 24 μm “wing” (a curved southwestern coma) feature at 352,000 km (90″) from the nucleus attributed by Stansberry et al. to nucleus rotation and instead propose that it is largely created by solar radiation pressure and gravity acting on micron-sized grains. We performed coma removal to the 16 μm PU image in order to refine the nucleus’ emitted thermal flux. A new application of the Near Earth Asteroid Thermal Model at five wavelengths (5.730, 7.873, 15.80, 23.68, and 71.42 μm) was then used to refine SW1's effective radius measurement to R = 32.3 ± 3.1 km and infrared beaming parameter to η = 1.1 ± 0.2, respectively.

The Near-Earth Object Surveillance Mission (NEOSM) will provide unprecedented detection, tracking and characterization of Near-Earth Objects (NEOs) using high-cadence imaging from a space-based infrared telescope. Planning for the NEOSM requires an accurate model of the solar system’s small body populations in order to develop efficient operational survey strategies and to assess survey performance once in-flight operations have commenced. The NEOSM Investigation Team is currently developing the Reference Small Body Population Model (RSBPM; [1]) that will contain the current best estimates of the dynamical and physical properties of the solar system’s small body populations. Development of the RSBPM will be completed before the NEOSM launch, and the finished product will be peer-reviewed to ensure accuracy. Once the survey begins, we will compare predictions based on the RSBPM to actual observational measurements to calculate the efficiency of the survey, and thus de-bias the survey to properly characterize each population in order to assess Earth impact risks. We present here an update to the methods of incorporating comets into the RSBPM, with particular focus on accurately incorporating dust and CO+CO2 gas comae activity behaviors. A better understanding of these physical characteristics are relevant for planetary defense (e.g., determining nuclei diameters). The high abundance of volatile ices (e.g., H2O, CO, CO2) present in comet nuclei drives outgassing and dust lofting when the surface material is exposed to the Sun, generating comae and tails. While high-cadence and long-baseline observational campaigns producing physical characterization of nuclei and comae exist for a few comets (e.g. 1P/Halley, 9P/Tempel, 67P/Churyumov-Gerasimenko, C/1995 O1 (Hale-Bopp), C/2012 S1 (ISON)) and have allowed determination of single-apparition secular light curves, predictions for the behaviors of an individual comet are notoriously difficult due to the possibility of outbursts, fragmentation events, complete nucleus disintegration and seasonal effects. This high degree of uncertainty for cometary behaviors introduces complications for modeling the brightening trends for individual comets as compared to those for the asteroid populations. Fortunately, characterizing the behaviors of comets in the infrared as an ensemble population is a somewhat more tractable problem. Previous (e.g., COBE [2], AKARI [3], Spitzer [4]) and ongoing surveys (e.g, Pan-STARRS [5], Zwicky Transient Facility [6], ATLAS [7], WISE/NEOWISE [8]) detecting large numbers of comets in the infrared are allowing a framework through which an individual comet’s activity behaviors can be estimated based on behavior trends in infrared emission of the larger ensemble. We are utilizing derived ensemble properties from these observational campaigns to develop a recipe for best simulating the morphological and photometric behaviors for the solar system’s comet populations. NEOSM will utilize a space-based 50-cm aperture infrared-optimized telescope located at the Sun-Earth L1 Lagrange position. It will contain a single instrument with a dual-channel infrared imaging camera that will survey the sky in bandpasses at 4-5.2 microns (denoted NC1) and 6-10 microns (denoted NC2). NC1 images of comets will mostly contain thermal emission (for comets within ~3 au of the Sun) from the nucleus and any dust coma/tail/trail. Additionally, the bandpass of NC1 covers the CO2 gas ν3 vibrational mode emission band centered at 4.26 microns and the CO gas vibrational mode emission band centered at 4.67 microns, which will allow detection of a comet’s combined CO+CO2 gas coma. This method of detecting such cometary volatiles via broadband imaging has had much success in the past with Spitzer (e.g. [4, 9]) and WISE/NEOWISE (e.g. [10, 11]). The longer wavelength NC2 images of comets will measure thermal emission from nuclei and dust. Because of the particular bandpasses of NC1 and NC2 we are currently focusing on developing methods of modeling cometary activity behaviors utilizing derived (1) nuclei cumulative size distributions, (2) dust activity behaviors as characterized by empirical trends of the εfρ parameter and (3) CO and CO2 gas comae trends based on the previously mentioned past and ongoing surveys. Future efforts by the NEOSM Investigation Team will focus on incorporation of other characteristic cometary phenomena (e.g., dust tails and trails) to help refine expected detection efficiencies and coma and/or tail flux removal for robust nucleus size estimation. Acknowledgements NEOSM is a project sponsored by NASA’s Planetary Defense Coordination Office, a division of NASA’s Planetary Science Directorate. References [1] Lilly (Schunova) et al., 2020, AAS Meeting Abstracts, 385.04. [2] Lisse et al., 2002, IAU Colloq. 181, Vol. 15, 259. [3] Ootsubo et al., 2012, ApJ, 752:15. [4] Fernandez et al., 2013, Icarus, 226, Issue 1. [5] Denneau et al., 2013, PASP, 125:926. [6] Masci et al., 2019, PASP, 131:995. [7] Tonry et al., 2018, PASP, 130:988. [8] Mainzer et al., 2011, ApJ, 731:53. [9] Kelley et al., 2013, Icarus, 225:475. [10] Bauer et al., 2015, ApJ, 814:85. [11] Bauer et al., 2017, AJ, 154:53.

Centaurs are small bodies orbiting in the giant planet region that were scattered inward from their source populations beyond Neptune. Some members of the population display comet-like activity during their transition through the solar system, the source of which is not well understood. The range of heliocentric distances where the active Centaurs have been observed and their median lifetime in the region suggest that this activity is driven neither by water-ice sublimation nor entirely by supervolatiles. Here we present an observational and thermodynamical study of 13 Centaurs discovered in the Pan-STARRS1 detection database aimed at identifying and characterizing active objects beyond the orbit of Jupiter. We find no evidence of activity associated with any of our targets at the time of their observations with the Gemini North telescope in 2017 and 2018, or in archival data from 2013 to 2019. Upper limits on the possible volatile and dust production rates from our targets are 1–2 orders of magnitude lower than production rates in some known comets and are in agreement with values measured for other inactive Centaurs. Our numerical integrations show that the orbits of six of our targets evolved interior to r ∼ 15 au over the past 100,000 yr, where several possible processes could trigger sublimation and outgassing, but their apparent inactivity indicates that either their dust production is below our detection limit or the objects are dormant. Only one Centaur in our sample—2014 PQ70—experienced a sudden decrease in semimajor axis and perihelion distance attributed to the onset of activity for some previously known inactive Centaurs, and therefore it is the most likely candidate for any future outburst. This object should be a target of high interest for any further observational monitoring.

We present analysis of five nights of R-band observations of Comet 29P/Schwassmann-Wachmann 1 (SW1) taken on September 2008 which show the comet undergoing an outburst. Coma morphology shows a projected asymmetric shell of material expanding radially and four linear features on the northern side of the coma at position angles 37°, 78°, 300°, and 353°. Using the measured projected radial outflow velocity of 0.11 ±0.02 km/s for the shell material, we calculate an outburst time of UT 2008-09-21.03 ±0.95 days. By tracking the inner and outer extent of the northern linear features, we found that the features are fully contained within the expanding shell of material. This suggested both shell and linear features originated during the same event and activity originating from different regions on the nuclear surface are not necessary to generate both types of morphological structure observed. A 3-D Monte Carlo coma model was used to model the outburst. Morphological features present in the observations were modeled allowing constraints to be placed on the spin state of SW1’s nucleus. The evolution of morphological features allows constraints on the rotation period P assuming an outburst duration Δt and the spin period constraints are expressed in terms of their ratio P/Δt. Since the spin-pole orientation could not be constrained, four spin-pole orientations were chosen for modeling the coma. Spin-period constraints for each assumed pole orientation are discussed. Overall, modeling suggested either a spin period on the order of days, a spin-pole orientation nearly along the sub-Earth direction, or a combination of both. To place an independent constraint on the outburst duration, radial surface-brightness profiles of the observations were compared with profiles from synthetic models, giving an upper-limit of Δt ≤ 1.5 days. Longer outbursts resulted in a higher number of dust grains in close proximity to the nucleus during the observations and a profile slope too steep to model observations. Lastly, from photometry of the five nights of observation, a lower limit of (1.8 ± 0.07) × 109 kg was estimated for the total amount of dust emitted during the outburst. Assuming the outburst was triggered by either the sublimation of pure CO or CO2 ice and a dust to gas ratio of ∼4 (Rosetta results for Comet 67P, Rotundi et al. 2015), a lower limit for the outburst duration on the order of hours was obtained.

We present analysis of {\it Hubble Space Telescope} (HST) observations of Centaur 29P/Schwassmann-Wachmann 1 (SW1) while in outburst to characterize the outburst coma and place constraints on the nucleus' spin state. The observations consist of Wide Field and Planetary Camera 2 (WFPC2) images from Cycle 5, GO-5829 (Feldman (1995)) acquired on UT 1996 March 11.3 and 12.1, which serendipitously imaged the Centaur shortly after a major outburst. A multi-component coma was detected consisting of: an expanding outburst dust coma with complex morphology possessing an east-west asymmetry and north-south symmetry contained within 5$''$ ($\sim$19,000 km) of the nucleus, the residual dust shell of an earlier UT 1996 February outburst, and a nearly circular underlying quiescent activity level coma detectable to $\sim$70$''$ ($\sim$267,000 km) away from the nucleus. Photometry of the calibrated WFPC2 images resulted in a measured 5$''$ radius aperture equivalent R-band magnitude of 12.86 $\pm$ 0.02 and an estimated (2.79 $\pm$ 0.05)$\times 10^8$ kg for the lower limit of dust material emitted during the outburst. No appreciable evolution of morphologic features, indicating signatures of nucleus rotation, were detected between the two imaging epochs. The observations were modeled using a 3-D Monte Carlo coma model (Samarasinha (2000)) to place constraints on the nucleus' rotation state. Modeling indicated the morphology is representative of a non-isotropic ejection of dust emitted during a single outburst event with a duration on the order of hours from a single source region corresponding to $\sim$1\% of the surface area. A spin period with lower limit on the order of days is suggested to reproduce the coma morphology seen in the observations.

The recently discovered object P/2019 LD2 (ATLAS) was initially thought to be a Jupiter Trojan asteroid, until dynamical studies and the appearance of persistent cometary activity revealed that this object is actually an active Centaur. However, the dynamical history, thermal environment, and impact of such environments on the activity of 2019 LD2 are poorly understood. Here we conduct dynamical simulations to constrain its orbital history and resulting thermal environment over the past 3000 years. We find that 2019 LD2 is currently in the vicinity of a dynamical "Gateway" that facilitates the majority of transitions from the Centaur population into the Jupiter Family of Comets (JFC population; Sarid et al. 2019). Our calculations show that it is unlikely to have spent significant amounts of time in the inner solar system, suggesting that its nucleus is relatively pristine in terms of physical, chemical, and thermal processing through its history. This could explain its relatively high level of distant activity as a recently activated primordial body. Finally, we find that the median frequency of transition from the Gateway population into the JFC population varies from once every ~3 years to less than once every 70 years, if 2019 LD2's nucleus is ~1 km in radius or greater than 3 km in radius. Forward modeling of 2019 LD2 shows that it will transition into the JFC population in 2063, representing the first known opportunity to observe the evolution of an active Centaur nucleus as it experiences this population-defining transition., Submitted to AAS Journals for publication

We report on $g$, $r$ and $i$ band observations of the Interstellar Object 'Oumuamua (1I) taken on 2017 October 29 from 04:28 to 08:40 UTC by the Apache Point Observatory (APO) 3.5m telescope's ARCTIC camera. We find that 1I's colors are $g-r=0.41\pm0.24$ and $r-i=0.23\pm0.25$, consistent with the visible spectra of Masiero (2017), Ye et al. (2017) and Fitzsimmons et al. (2017), and most comparable to the population of Solar System C/D asteroids, Trojans, or comets. We find no evidence of any cometary activity at a heliocentric distance of 1.46 au, approximately 1.5 months after 1I's closest approach distance to the Sun. Significant brightness variability was seen in the $r$ observations, with the object becoming notably brighter towards the end of the run. By combining our APO photometric time series data with the Discovery Channel Telescope (DCT) data of Knight et al. (2017), taken 20 h later on 2017 October 30, we construct an almost complete light curve with a most probable lightcurve period of $P \simeq 4~{\rm h}$. Our results imply a double peaked rotation period of 8.1 $\pm$ 0.02 h, with a peak-to-peak amplitude of 1.5 - 2.1 mags. Assuming that 1I's shape can be approximated by an ellipsoid, the amplitude constraint implies that 1I has an axial ratio of 3.5 to 10.3, which is strikingly elongated. Assuming that 1I is rotating above its critical break up limit, our results are compatible with 1I having having modest cohesive strength and may have obtained its elongated shape during a tidal disruption event before being ejected from its home system. Astrometry useful for constraining 1I's orbit was also obtained and published in Weaver et al. (2017)., Comment: 13 pages, 6 figures, 1 table, accepted for publication in the Astrophysical Journal Letters, data are available at: https://github.com/dhuppenkothen/CometPeriodSearch and https://zenodo.org/record/1068392

We present a new analysis of Spitzer observations of Comet 29P/Schwassmann–Wachmann 1 taken on UT 2003 November 21, 23, and 24, similar to a previous investigation of the observations (Stansberry et al., 2004), but using the most recent Spitzer data pipeline products and intensive image processing techniques. Analysis of images from the IRAC 5.8 and 8.0 μ m bands and the MIPS 24.0 and 70.0 μ m bands resulted in photometry measurements of the nucleus after a suite of coma modeling and removal processes were implemented. SW1 was not identified in the 5.8 μ m image from the previous work so its incorporation into this analysis is entirely new. Using the Near Earth Asteroid Thermal Model (Harris, 1998) resulted in a nucleus radius measurement of R = 30.2 - 2.9 + 3.7 km and an infrared beaming parameter value of η = 0.99 - 0.19 + 0.26 . We also measured an infrared geometric albedo, p 5.8 = 0.5 ± 0.5 . Extrapolating a 0.04 V-band albedo and using a normalized reflectivity gradient S ′ = 14.94 ± 1.09 [% (1000 A) −1 ] (Duffard, R., et al. [2014]. Astron. Astrophys. 564, A92) we recover an infrared albedo of p 5.8 = 0.31 in the near infrared consistent with the value recovered from thermal modeling. The dust composition extracted from IRS spectra are very comet-like, containing mainly amorphous ferromagnesian silicates (but with a minority of crystalline silicates as well), water ice, and metal sulfides.