Analysis of Nucleus Properties of the Enigmatic Comet 29P/Schwassmann-Wachmann 1

We present results from a continuing effort to understand activity drivers for the enigmatic Comet 29P/Schwassmann-Wachmann 1 (SW1). SW1 has been of interest since its discovery almost 100 years ago because of its nearly continuous, quiescent activity beyond the water-sublimation line and its highly variable, outburst activity while receiving a nearly constant insolation due to its low eccentricity orbit. These characteristics make SW1 a useful target for investigating both distant cometary activity drivers and also cometary outburst behavior. We approach answering these questions through a detailed analysis of SW1; first by measuring nucleus properties required for a more accurate nucleus thermophysical modeling and second, by applying thermal modeling to replicate its activity. Our project began with an analysis of Spitzer Space Telescope infrared observations of SW1 from 2003. Coma removal techniques when applied to the images provided nucleus photometry measurements. Application of the Near Earth Asteroid Thermal Model (NEATM) to these measured photometry values resulted in an effective nucleus radius of 32.3 ± 3.1 km and a thermal beaming parameter of 1.14 ± 0:22. These results indicated that SW1 is one of the largest Jupiter Family Comets and also has a relatively smooth overall surface and/or a low thermal inertia. We next placed constraints on the nucleus\u27 spin state through analysis of evolution seen in the coma\u27s morphological structure through two sets of outburst coma observations. The first set analyzed are from the Kitt Peak 2.1-m telescope taken ± 2 days after a major outburst in 2008. 3-D Monte Carlo coma modeling showed that the nucleus\u27 spin period is on the order of days and/or the spin pole orientation was along the Earth\u27s directions during observations. The second set are Hubble Space Telescope observations from 1996 taken ± 15 hours after a major outburst. Modeling similarly showed a rotation period on the order of days. Due to the observing geometry differing between the 2008 and 1996 observations, we conclude the rotation period lower limit must be on the order of days even if the spin-pole direction was directed along the sub-Earth direction during one set of observations. The nucleus properties measured or constrained by our project were incorporated into a thermophysical model to replicate the quiescent activity via the sublimation of the supervolatile species CO or CO2. A progenitor nucleus was thermally evolved in SW1\u27s current orbit using different plausible nucleus interior compositional and layering schemes. We discuss results of this analysis and additionally possibilities for future thermal modeling efforts

Semi-major Axis Jumps as the Activity Trigger in Centaurs and High-Perihelion Jupiter Family Comets

We present a dynamical study of 39 active Centaurs and 17 high-perihelion (q$>$4.5 au) JFCs with a focus on investigating recent orbital changes as potential triggers for comet-like activity. We have identified a common feature in the recent dynamical histories of all active Centaurs and JFC in our sample that is not present in the history of the majority of inactive population members: a sharp decrease in semi-major axis and eccentricity occurring within the last several hundred years prior to observed activity. We define these rapid orbital changes as `a-jumps'. Our results indicate that these orbital reshaping events lead to shorter orbital periods and subsequently greater average per-orbit heating of Centaur nuclei. We suggest the a-jumps could therefore be a major trigger of cometary activity on Centaurs and JFCs. Our results further imply that analyses of the recent dynamical histories could be used to identify objects that are currently active or may become active soon, where we have identified three such Centaurs with recent a-jumps that should be considered high-priority targets for observational monitoring to search for activity.Comment: 19 pages, 4 figures, 1 table, accepted for publication in ApJ

First detection of CO2_2 emission in a Centaur: JWST NIRSpec observations of 39P/Oterma

Centaurs are minor solar system bodies with orbits transitioning between those of Trans-Neptunian Scattered Disk objects and Jupiter Family comets. 39P/Oterma is a frequently active Centaur that has recently held both Centaur and JFC classifications and was observed with the JWST NIRSpec instrument on 2022 July 27 UTC while it was 5.82 au from the Sun. For the first time, CO$_2$ gas emission was detected in a Centaur, with a production rate of Q$_{CO_2}$ = (5.96 $\pm$ 0.80) $\times$ 10$^{23}$ molecules s$^{-1}$. This is the lowest detection of CO$_2$ of any Centaur or comet. CO and H$_2$O were not detected down to constraining upper limits. Derived mixing ratios of Q$_{CO}$/Q$_{CO_2}$ $\leq$2.03 and Q$_{CO_2}$/Q$_{H_2O}$ $\geq$0.60 are consistent with CO$_2$ and/or CO outgassing playing large roles in driving the activity, but not water, and show a significant difference between the coma abundances of 29P/Schwassmann-Wachmann 1, another Centaur at a similar heliocentric distance, which may be explained by thermal processing of 39P's surface during its previous Jupiter-family comet orbit. To help contextualize the JWST data we also acquired visible CCD imaging data on two dates in July (Gemini North) and September (Lowell Discovery Telescope) 2022. Image analysis and photometry based on these data are consistent with a point source detection and an estimated effective nucleus radius of 39P in the range of $R_{nuc}=$2.21 to 2.49~km

Tuning the Sensitivity of an Optical Cavity with Slow and Fast Light

We have measured mode pushing by the dispersion of a rubidium vapor in a Fabry-Perot cavity and have shown that the scale factor and sensitivity of a passive cavity can be strongly enhanced by the presence of such an anomalous dispersion medium. The enhancement is the result of the atom-cavity coupling, which provides a positive feedback to the cavity response. The cavity sensitivity can also be controlled and tuned through a pole by a second, optical pumping, beam applied transverse to the cavity. Alternatively, the sensitivity can be controlled by the introduction of a second counter-propagating input beam that interferes with the first beam, coherently increasing the cavity absorptance. We show that the pole in the sensitivity occurs when the sum of the effective group index and an additional cavity delay factor that accounts for mode reshaping goes to zero, and is an example of an exceptional point, commonly associated with coupled non-Hermitian Hamiltonian systems. Additionally we show that a normal dispersion feature can decrease the cavity scale factor and can be generated through velocity selective optical pumpin

Water, hydrogen cyanide, carbon monoxide, and dust production from distant comet 29P/Schwassmann-Wachmann 1

peer reviewedContext. 29P/Schwassmann-Wachmann 1 is a distant Centaur/comet, showing persistent CO-driven activity and frequent outbursts. Aims: We aim to better characterize its gas and dust activity from multiwavelength observations performed during outbursting and quiescent states. Methods: We used the HIFI, PACS and SPIRE instruments of the Herschel space observatory on several dates in 2010, 2011, and 2013 to observe the H2O 557 GHz and NH3 573 GHz lines and to image the dust coma in the far-infrared. Observations with the IRAM 30 m telescope were undertaken in 2007, 2010, 2011, and 2021 to monitor the CO production rate through the 230 GHz line, and to search for HCN at 89 GHz. The 70 and 160 µm PACS images were used to measure the thermal flux from the nucleus and the dust coma. Modeling was performed to constrain the size of the sublimating icy grains and to derive the dust production rate. Results: HCN is detected for the first time in comet 29P (at 5σ in the line area). H2O is detected as well, but not NH3. H2O and HCN line shapes differ strongly from the CO line shape, indicating that these two species are released from icy grains. CO production rates are in the range (2.9-5.6) × 10E28 s−1 (1400-2600 kg s−1). A correlation between the CO production rate and coma brightness is observed, as is a correlation between CO and H2O production. The correlation obtained between the excess of CO production and excess of dust brightness with respect to the quiescent state is similar to that established for the continuous activity of comet Hale-Bopp. The measured Q(H2O)/Q(CO) and Q(HCN)/Q(CO) production rate ratios are 10.0 ± 1.5 % and 0.12 ± 0.03 %, respectively, averaging the April-May 2010 measurements (Q(H2O) = (4.1 ± 0.6) × 10E27 s−1, Q(HCN) = (4.8 ± 1.1) × 10E25 s−1). We derive three independent and similar values of the effective radius of the nucleus, ~31 ± 3 km, suggesting an approximately spherical shape. The inferred dust mass-loss rates during quiescent phases are in the range 30-120 kg s−1, indicating a dust-to-gas mass ratio <0.1 during quiescent activity. We conclude that strong local heterogeneities exist on the surface of 29P, with quenched dust activity from most of the surface, but not in outbursting regions. Conclusions: The volatile composition of the atmosphere of 29P strongly differs from that of comets observed within 3 au from the Sun. The observed correlation between CO, H2O and dust activity may provide important constraints for the outburst-triggering mechanism

29P/Schwassmann-Wachmann: A Rosetta Stone for Amorphous Water Ice and CO <-> CO2 Conversion in Centaurs and Comets?

Centaur 29P/Schwassmann-Wachmann 1 (SW1) is a highly active object orbiting in the transitional Gateway region (Sarid et al. 2019) between the Centaur and Jupiter Family Comet regions. SW1 is unique among the Centaurs in that it experiences quasi-regular major outbursts and produces CO emission continuously; however, the source of the CO is unclear. We argue that due to its very large size (approx. 32 km radius), SW1 is likely still responding, via amorphous water ice (AWI) conversion to crystalline water ice (CWI), to the rapid change in its external thermal environment produced by its dynamical migration from the Kuiper belt to the Gateway Region at the inner edge of the Centaur region at 6 au. It is this conversion process that is the source of the abundant CO and dust released from the object during its quiescent and outburst phases. If correct, these arguments have a number of important predictions testable via remote sensing and in situ spacecraft characterization, including: the quick release on Myr timescales of CO from AWI conversion for any few km-scale scattered disk KBO transiting into the inner system; that to date SW1 has only converted between 50 to 65% of its nuclear AWI to CWI; that volume changes upon AWI conversion could have caused subsidence and cave-ins, but not significant mass wasting or crater loss on SW1; that SW1s coma should contain abundant amounts of CWI CO2-rich icy dust particles; and that when SW1 transits into the inner system within the next 10,000 years, it will be a very different kind of JFC comet.Comment: 29 Pages, 3 Figures, 2 Tables, accepted 16-Sept-2022 by the Planetary Science Journal Corrected proof version 26-Oct-202

Physical and dynamical characterization of hyperbolic comet C/2017 U7(PANSTARRS)

We present here a dynamical and observational study of the comet C/2017 U7 (PANSTARRS). This comet was discovered in 2017 and found to have a hyperbolic orbit. Our dynamical analysis shows that the object has probably originated in the Oort cloud, however an interstellar origin cannot be discarded. The observations were obtained in 2018 and 2019 using the Goodman High Throughput Spectrograph (GHTS) at the SOAR telescope. We obtained visible spectra covering the wavelength range of and also images in the SDSS filters system. Both the low-resolution reflectance spectrum and the reflectance spectra derived from the SDSS filters show an atypical band at . We conducted a comparative study of the colors and reflectance spectra of different small body populations (e.g., comets, Centaurs, and trans-Neptunian objects or TNOs) from the literature and concluded that the spectra and the colors of this comet are atypical, showing only some overlap with those of some known members of the TNOs and Centaurs, within the large uncertainties of the measurements of those populations. It is found that the feature and overall spectral shape can be reproduced by laboratory spectra of kerite, a template for aliphatic-rich hydrocarbons that has been previously identified in NIR cometary spectra absorptions. It is tentatively proposed that the unusual spectral shape is the result of a particle size distribution of dust grains in the coma or on the surface that has arisen due to a low grain ejection velocity from the surface and large nucleus size