More Like this

1. First Detection of CO 2 Emission in a Centaur: JWST NIRSpec Observations of 39P/Oterma

   https://doi.org/10.3847/PSJ/acf928  

   Pinto, O. Harrington ; Kelley, M. S. P. ; Villanueva, G. L. ; Womack, M. ; Faggi, S. ; McKay, A. ; DiSanti, M. A. ; Schambeau, C. ; Fernandez, Y. ; Bauer, J. ; et al ( November 2023 , The Planetary Science Journal)

   Centaurs are minor solar system bodies with orbits transitioning between those of trans-Neptunian scattered disk objects and Jupiter-family comets (JFCs). 39P/Oterma (39P) 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, CO₂gas emission was detected in a centaur, with a production rate of$Q_{{\mathrm{CO}}_2}$= (5.96 ± 0.80) × 10²³molecules s⁻¹. This is the lowest detection of CO₂of any centaur or comet. CO and H₂O were not detected down to constraining upper limits. Derived mixing ratios ofQ_CO/Q${}_{{\mathrm{CO}}_2}$≤ 2.03 and$Q_{{\mathrm{CO}}_2}$/Q${}_{{\mathrm{H}}_2\mathrm{O}}$≥ 0.60 are consistent with CO₂and/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 JFC orbit. To help contextualize the JWST data we also acquired visible CCD imaging data on two dates in 2022 July (Gemini-North) and September (Lowell Discovery Telescope). 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 ofR_nuc= 2.21–2.49 km.

    

   more » « less
2. Possible Activity in 468861 (2013 LU28)

   https://doi.org/10.3847/PSJ/ac480d  

   Slemp, Lily A. ; Meech, Karen J. ; Bufanda, Erica ; Kleyna, Jan T. ; Hainaut, Olivier ; Bauer, James ; Weryk, Robert ; Denneau, Larry ; Keane, Jacqueline V. ; Bhatt, Bhuwan C. ; et al ( February 2022 , The Planetary Science Journal)

   Manx comets are objects on long-period comet orbits that are inactive as they approach perihelion. They are of particular interest because they may help constrain solar system formation models. 2013 LU28 was discovered as an inactive asteroidal object on 2013 June 8 at a heliocentric distance of 21.8 au. Images and photometric data were obtained of 2013 LU28 from multiple telescopes from pre-discovery data in 2010 until the present. Its spectral reflectivity is consistent with typical organic-rich comet surfaces with colors of$g\prime -r\prime$= 0.97 ± 0.02,$r\prime -i\prime$= 0.43 ± 0.02, and$r\prime -z\prime$= 0.65 ± 0.03, corresponding to a spectral reflectivity slope of 30 ± 3%/100 nm. There is no obvious indication of dust coma in deep stacked images. We estimate the nucleus radius to be ∼55.7 ± 0.3 km assuming an albedo of 4%. This is much smaller than the 1σupper limits on the nucleus size of 79.9 km from the NEOWISE survey assuming the same albedo, since the NEOWISE survey is not very sensitive to objects this small at this distance. The heliocentric light curve suggests possible activity betweenr∼ 17 and 13 au where 2013 LU28 is brighter than expected. This is consistent with outgassing from CO or CO₂. Using surface brightness profiles, we estimate an upper limit of ∼0.01 kg s⁻¹for micron-sized dust that can be produced without us detecting it for the inactive portion of the light curve, and upper limits of ∼1 kg s⁻¹for CO and ∼1.5 kg s⁻¹for CO₂between 20 and 14.7 au.

    

   more » « less
3. C/2014 UN 271 (Bernardinelli-Bernstein): The Nearly Spherical Cow of Comets

   https://doi.org/10.3847/2041-8213/ac32d3  

   Bernardinelli, Pedro H. ; Bernstein, Gary M. ; Montet, Benjamin T. ; Weryk, Robert ; Wainscoat, Richard ; Aguena, M. ; Allam, S. ; Andrade-Oliveira, F. ; Annis, J. ; Avila, S. ; et al ( November 2021 , The Astrophysical Journal Letters)

   Comet C/2014 UN₂₇₁(Bernardinelli-Bernstein), incoming from the Oort cloud, is remarkable in having the brightest (and presumably largest) nucleus of any well-measured comet and having been discovered at the heliocentric distancer_h≈ 29 au, farther than any Oort cloud comet. In this work, we describe the discovery process and observations and the properties that can be inferred from images recorded until the first reports of activity in 2021 June. The orbit hasi= 95°, with a perihelion of 10.97 au to be reached in 2031 and a previous aphelion at 40,400 ± 260 au. Backward integration of the orbit under a standard Galactic tidal model and known stellar encounters suggests a perihelion ofq≈ 18 au on its previous perihelion passage 3.5 Myr ago; hence, the current data could be the first ever obtained of a comet that has not been inside Uranus’s orbit in 4 Gyr. The photometric data show an unresolved nucleus with absolute magnitudeH_r= 8.0, colors that are typical of comet nuclei or Damocloids, and no secular trend as it traversed the range 34–23 au. For ther-band geometric albedop_r, this implies a diameter of$150{(p_r/0.04)}^{-0.5}$km. There is strong evidence of brightness fluctuations at the ±0.2 mag level, but no rotation period can be discerned. A coma, nominally consistent with a “stationary” 1/ρsurface brightness distribution, grew in scattering cross section at an exponential rate fromAfρ≈ 1 to ≈150 m as the comet approached from 28 to 20 au. The activity rate is consistent with a very simple model of sublimation of a surface species in radiative equilibrium with the Sun. The inferred enthalpy of sublimation matches those of CO₂and NH₃. More volatile species, such as N₂, CH₄, and CO, must be far less abundant on the sublimating surfaces.

    

   more » « less
4. Coma Abundances of Volatiles at Small Heliocentric Distances: Compositional Measurements of Long-period Comet C/2020 S3 (Erasmus)

   https://doi.org/10.3847/1538-3881/ad0e02  

   Ejeta, Chemeda ; Gibb, Erika ; Roth, Nathan ; DiSanti, Michael A. ; Dello Russo, Neil ; Saki, Mohammad ; McKay, Adam J. ; Kawakita, Hideyo ; Khan, Younas ; Bonev, Boncho P. ; et al ( December 2023 , The Astronomical Journal)

   We report production rates of H₂O and nine trace molecules (C₂H₆, CH₄, H₂CO, CH₃OH, HCN, NH₃, C₂H₂, OCS, and CO) in long-period comet C/2020 S3 (Erasmus) using the high-resolution, cross-dispersed infrared spectrograph (iSHELL) at the NASA Infrared Telescope Facility, on two pre-perihelion dates at heliocentric distancesR_h= 0.49 and 0.52 au. Our molecular abundances with respect to simultaneously or contemporaneously measured H₂O indicate that S3 is depleted in CH₃OH compared to its mean abundance relative to H₂O among the overall comet population (Oort Cloud comets and Jupiter-family comets combined), whereas the eight other measured species have near-average abundances relative to H₂O. In addition, compared to comets observed atR_h< 0.80 au at near-infrared wavelengths, S3 showed enhancement in the abundances of volatile species H₂CO, NH₃, and C₂H₂, indicating possible additional (distributed) sources in the coma for these volatile species. The spatial profiles of volatile species in S3 in different instrumental settings are dramatically different, which might suggest temporal variability in comet outgassing behavior between the nonsimultaneous measurements. The spatial distributions of simultaneously measured volatile species C₂H₆and CH₄are nearly symmetric and closely track each other, while those of CO and HCN co-measured with H₂O (using different instrument settings) are similar to each other and are asymmetric in the antisunward direction.

    

   more » « less
5. A SUBLIME 3D Model for Cometary Coma Emission: The Hypervolatile-rich Comet C/2016 R2 (PanSTARRS)

   https://doi.org/10.3847/1538-4357/ac5893  

   Cordiner, M. A. ; Coulson, I. M. ; Garcia-Berrios, E. ; Qi, C. ; Lique, F. ; Zołtowski, M. ; de Val-Borro, M. ; Kuan, Y. -J. ; Ip, W. -H. ; Mairs, S. ; et al ( April 2022 , The Astrophysical Journal)

   The coma of comet C/2016 R2 (PanSTARRS) is one of the most chemically peculiar ever observed, in particular due to its extremely high CO/H₂O and${\mathrm{N}}_2^{+}$/H₂O ratios, and unusual trace volatile abundances. However, the complex shape of its CO emission lines, as well as uncertainties in the coma structure and excitation, has lead to ambiguities in the total CO production rate. We performed high-resolution, spatially, spectrally, and temporally resolved CO observations using the James Clerk Maxwell Telescope and Submillimeter Array to elucidate the outgassing behavior of C/2016 R2. Results are analyzed using a new, time-dependent, three-dimensional radiative transfer code (SUBlimating gases in LIME; SUBLIME, based on the open-source version of the LIne Modeling Engine), incorporating for the first time, accurate state-to-state collisional rate coefficients for the CO–CO system. The total CO production rate was found to be in the range of (3.8 − 7.6) × 10²⁸s⁻¹between 2018 January 13 and February 1 (atr_H= 2.8–2.9 au), with a mean value of (5.3 ± 0.6) × 10²⁸s⁻¹. The emission is concentrated in a near-sunward jet, with a half-opening angle of ∼62° and an outflow velocity of 0.51 ± 0.01 km s⁻¹, compared to 0.25 ± 0.01 km s⁻¹in the ambient (and nightside) coma. Evidence was also found for an extended source of CO emission, possibly due to icy grain sublimation around 1.2 × 10⁵km from the nucleus. Based on the coma molecular abundances, we propose that the nucleus ices of C/2016 R2 can be divided into a rapidly sublimating apolar phase, rich in CO, CO₂, N₂, and CH₃OH, and a predominantly frozen (or less abundant), polar phase containing more H₂O, CH₄, H₂CO, and HCN.

    

   more » « less