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1. Rotational Study of 5:3 and 7:4 Resonant Objects within the Main Classical Trans-Neptunian Belt

   https://doi.org/10.3847/PSJ/ad2933  

   Thirouin, Audrey ; Sheppard, Scott S. ( April 2024 , The Planetary Science Journal)

   The 5:3 and 7:4 mean motion resonances of Neptune are at 42.3 and 43.7 au, respectively, and overlap with objects in the classical trans-Neptunian belt (Kuiper Belt). We report the complete/partial lightcurves of 13 and 14 trans-Neptunian objects (TNOs) in the 5:3 and 7:4 resonances, respectively. We report a most likely contact binary in the 7:4 resonance, 2013 FR₂₈, with a periodicity of 13.97 ± 0.04 hr and a lightcurve amplitude of 0.94 ± 0.02 mag. With a V-/U-shaped lightcurve, 2013 FR₂₈has one of the largest well-sampled TNO amplitudes observed with ground-based observations, comparable to the well-determined contact binary 2001 QG₂₉₈. 2013 FR₂₈has a mass ratioq∼ 1 with a densityρ∼ 1 g cm⁻³. We find several objects with large amplitudes and classify 2004 SC₆₀, 2006 CJ₆₉, and 2013 BN₈₂as likely contact binaries and 2001 QF₃₃₁, 2003 YW₁₇₉, and 2015 FP₃₄₅as likely elongated objects. We observe the 17:9 resonant or classical object 2003 SP₃₁₇that we classify as a likely contact binary. A lower estimate of 10%–50% and 20%–55% for the fraction of (nearly) equal-sized contact binaries is calculated in the 5:3 and 7:4 resonances, respectively. Surface colors of 2004 SC₆₀, 2013 BN₈₂, 2014 OL₃₉₄, and 2015 FP₃₄₅have been obtained. Including these colors with ones from the literature reveals that elongated objects and contact binaries share the same ultrared surface color, except Manwë–Thorondor and 2004 SC₆₀. Not only are the colors of the 7:4 and 5:3 TNOs similar to the cold classicals, but we demonstrate that the rotational properties of the 5:3 and 7:4 resonants are similar to those of the cold classicals, inferring a clear link between these subpopulations.

    

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2. Lightcurves and Rotations of Trans-Neptunian Objects in the 2:1 Mean Motion Resonance with Neptune

   https://doi.org/10.3847/PSJ/ac7ab8  

   Thirouin, Audrey ; Sheppard, Scott S. ( July 2022 , The Planetary Science Journal)

   We report the rotational lightcurves of 21 trans-Neptunian objects (TNOs) in Neptune’s 2:1 mean motion resonance obtained with the 6.5 m Magellan-Baade telescope and the 4.3 m Lowell Discovery Telescope. The main survey’s goal is to find objects displaying a large lightcurve amplitude that is indicative of contact binaries or highly elongated objects. In our sample, two 2:1 resonant TNOs showed a significant short-term lightcurve amplitude: 2002 VD₁₃₀and (531074) 2012 DX₉₈. The full lightcurve of 2012 DX₉₈infers a periodicity of 20.80 ± 0.06 hr and amplitude of 0.56 ± 0.03 mag, whereas 2002 VD₁₃₀rotates in 9.85 ± 0.07 hr with a 0.31 ± 0.04 mag lightcurve amplitude. Based on lightcurve morphology, we classify (531074) 2012 DX₉₈as a likely contact binary but 2002 VD₁₃₀as a likely single elongated object. Based on our sample and the lightcurves reported in the literature, we estimate the lower percentage of nearly equal-sized contact binaries at only 7%–14% in the 2:1 resonance, which is comparable to the low fraction reported for the dynamically cold classical TNOs. This low contact binary fraction in the 2:1 Neptune resonance is consistent with the lower estimate of the recent numerical modeling. We report the Sloang′,r′, andi′ surface colors of 2002 VD₁₃₀, which is an ultra-red TNO whereas 2012 DX₉₈is a very red object based on published surface colors.

    

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3. The DECam Ecliptic Exploration Project (DEEP). VI. First Multiyear Observations of Trans-Neptunian Objects

   https://doi.org/10.3847/1538-3881/ad1524  

   Smotherman, Hayden ; Bernardinelli, Pedro H. ; Portillo, Stephen K. N. ; Connolly, Andrew J. ; Kalmbach, J. Bryce ; Stetzler, Steven ; Jurić, Mario ; Bektešević, Dino ; Langford, Zachary ; Adams, Fred C. ; et al ( February 2024 , The Astronomical Journal)

   We present the first set of trans-Neptunian objects (TNOs) observed on multiple nights in data taken from the DECam Ecliptic Exploration Project. Of these 110 TNOs, 105 do not coincide with previously known TNOs and appear to be new discoveries. Each individual detection for our objects resulted from a digital tracking search at TNO rates of motion, using two-to-four-hour exposure sets, and the detections were subsequently linked across multiple observing seasons. This procedure allows us to find objects with magnitudesm_VR≈ 26. The object discovery processing also included a comprehensive population of objects injected into the images, with a recovery and linking rate of at least 94%. The final orbits were obtained using a specialized orbit-fitting procedure that accounts for the positional errors derived from the digital tracking procedure. Our results include robust orbits and magnitudes for classical TNOs with absolute magnitudesH∼ 10, as well as a dynamically detached object found at 76 au (semimajor axisa≈ 77 au). We find a disagreement between our population of classical TNOs and the CFEPS-L7 three-component model for the Kuiper Belt.

    

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4. Free Inclinations for Trans-Neptunian Objects in the Main Kuiper Belt

   https://doi.org/10.3847/1538-4365/ac559a  

   Huang, Yukun ; Gladman, Brett ; Volk, Kathryn ( April 2022 , The Astrophysical Journal Supplement Series)

   There is a complex inclination structure present in the trans-Neptunian object (TNO) orbital distribution in the main classical-belt region (between orbital semimajor axes of 39 and 48 au). The long-term gravitational effects of the giant planets make TNO orbits precess, but nonresonant objects maintain a nearly constant “free” inclination (I_free) with respect to a local forced precession pole. Because of the likely cosmogonic importance of the distribution of this quantity, we tabulate free inclinations for all main-belt TNOs, each individually computed using barycentric orbital elements with respect to each object’s local forcing pole. We show that the simplest method, based on the Laplace–Lagrange secular theory, is unable to give correct forcing poles for objects near theν₁₈secular resonance, resulting in poorly conservedI_freevalues in much of the main belt. We thus instead implemented an averaged Hamiltonian to obtain the expected nodal precession for each TNO, yielding significantly more accurate free inclinations for nonresonant objects. For the vast majority (96%) of classical-belt TNOs, theseI_freevalues are conserved to < 1° over 4 Gyr numerical simulations, demonstrating the advantage of using this well-conserved quantity in studies of the TNO population and its primordial inclination profile; our computed distributions only reinforce the idea of a very coplanar surviving “cold” primordial population, overlain by a largeI-width implanted “hot” population.

    

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5. Col-OSSOS: Evidence for a Compositional Gradient Inherited from the Protoplanetary Disk?

   https://doi.org/10.3847/PSJ/ace7d0  

   Marsset, Michaël ; Fraser, Wesley C. ; Schwamb, Megan E. ; Buchanan, Laura E. ; Pike, Rosemary E. ; Volk, Kathryn ; Peixinho, Nuno ; Benecchi, Susan ; Bannister, Michele T. ; Tan, Nicole J. ; et al ( September 2023 , The Planetary Science Journal)

   In the present-day Kuiper Belt, the number of compositional classes and the orbital distributions of these classes hold important cosmogonic implications for the solar system. The Colours of the Outer Solar System Origins Survey (Col-OSSOS) recently showed that the observed color distribution of small (H⪆ 6) trans-Neptunian objects (TNOs) can be accounted for by the existence of only two composition classes, named BrightIR and FaintIR, where the range of colors in each class can be modeled as mixtures of two material end-members. Here, we combine the high-precision photometric measurements of Col-OSSOS with those of previous surveys to investigate the orbital distribution of the two color classes and reinterpret the known color–inclination correlation of TNOs in the context of the BrightIR/FaintIR taxonomy. In addition to confirming the previously reported distinct orbital distributions of these classes, we identify a trend of increasing orbital inclinations toward the bluer end of the optical and near-infrared color distribution of BrightIR objects. Using the output of numerical simulations investigating the orbital evolution of TNOs during their scattering phase with Neptune, we show that this trend could reflect a composition gradient in the early protoplanetary disk, in the range of heliocentric distances over which TNOs from the BrightIR class accreted. However, tensions between this interpretation and the existence of blue contaminants among cold classical TNOs, and possible alternative origins for the detected correlation, currently bear uncertainty on our proposed interpretation.

    

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