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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)

   Abstract 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. The Plutino Population: An Abundance of Contact Binaries

   https://doi.org/https://doi.org/10.3847/1538-3881/aac0ff  

   Thirouin, A; Sheppard, S.S. (May 2018, The Astronomical journal)

   We observed 12 Plutinos over two separated years with the 4.3 m Lowell’s Discovery Channel Telescope. Here, we present the first light-curve data for those objects. Three of them (2014 JL80, 2014 JO80, and 2014 JQ80) display a large light-curve amplitude explainable by a single elongated object, but they are most likely caused by a contact binary system due to their light-curve morphology. These potential contact binaries have rotational periods from 6.3 to 34.9 hr and peak-to-peak light-curve variability between 0.6 and 0.8mag. We present partial light curves, allowing us to constrain the light-curve amplitude and the rotational period of another nine Plutinos. By merging our data with the literature, we estimate that up to ∼40% of the Plutinos could be contact binaries. Interestingly, we found that all of the suspected contact binaries in the 3:2 resonance are small with absolute magnitude H>6mag. Based on our sample and the literature, up to ∼50% of the small Plutinos are potential contact binaries. 

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3. A Possible Dynamically Cold Classical Contact Binary: (126719) 2002 CC249

   Thirouin, Audrey; Sheppard, Scott S. (November 2017, The Astronomical journal)

   Images of the Kuiper Belt object (126719) 2002CC249 obtained in 2016 and 2017 using the 6.5 m Magellan-Baade Telescope and the 4.3 m Discovery Channel Telescope are presented. A light curve with a periodicity of 11.87±0.01 hr and a peak-to-peak amplitude of 0.79±0.04 mag is reported. This high amplitude double-peaked light curve can be due to a single elongated body, but it is best explained by a contact binary system from its U-/V-shaped light curve. We present a simple full-width-at-half-maximum test that can be used to determine if an object is likely a contact binary or an elongated object based on its light curve. Considering that 2002CC249 is in hydrostatic equilibrium, a system with a mass ratio qmin=0.6, and a density ρmin=1 g cm−3, or less plausible a system with qmax=1, and ρmax=5 g cm−3 can interpret the light curve. Assuming a single Jacobi ellipsoid in hydrostatic equilibrium and an equatorial view, we estimate ρ>0.34 g cm−3, and a/b=2.07. Finally, we report a new color study showing that 2002CC249 displays an ultra red surface characteristic of a dynamically Cold Classical trans-Neptunian object. 

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4. Photometry of Outer Solar System Objects from the Dark Energy Survey. I. Photometric Methods, Light-curve Distributions, and Trans-Neptunian Binaries

   https://doi.org/10.3847/1538-4365/acf6bf  

   Bernardinelli, Pedro_H; Bernstein, Gary_M; Jindal, Nicholas; Abbott, T_M_C; Aguena, M.; Alves, O.; Andrade-Oliveira, F.; Annis, J.; Bacon, D.; Bertin, E.; et al (October 2023, The Astrophysical Journal Supplement Series)

   Abstract We report the methods of and initial scientific inferences from the extraction of precision photometric information for the >800 trans-Neptunian objects (TNOs) discovered in the images of the Dark Energy Survey (DES). Scene-modeling photometry is used to obtain shot-noise-limited flux measures for each exposure of each TNO, with background sources subtracted. Comparison of double-source fits to the pixel data with single-source fits are used to identify and characterize two binary TNO systems. A Markov Chain Monte Carlo method samples the joint likelihood of the intrinsic colors of each source as well as the amplitude of its flux variation, given the time series of multiband flux measurements and their uncertainties. A catalog of these colors and light-curve amplitudesAis included with this publication. We show how to assign a likelihood to the distributionq(A) of light-curve amplitudes in any subpopulation. Using this method, we find decisive evidence (i.e., evidence ratio <0.01) that cold classical (CC) TNOs with absolute magnitude 6 <H_r< 8.2 are more variable than the hot classical (HC) population of the sameH_r, reinforcing theories that the former form in situ and the latter arise from a different physical population. Resonant and scattering TNOs in thisH_rrange have variability consistent with either the HCs or CCs. DES TNOs withH_r< 6 are seen to be decisively less variable than higher-H_rmembers of any dynamical group, as expected. More surprising is that detached TNOs are decisively less variable than scattering TNOs, which requires them to have distinct source regions or some subsequent differential processing. 

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5. An attempt to constrain Planet Nine’s orbit and position via resonant confinement of distant TNOs

   https://doi.org/10.1093/mnras/staa790  

   Downey, Brynna G; Morbidelli, Alessandro (May 2020, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We considered four TNOs on elongated orbits with small semimajor axis uncertainties: Sedna, 2004 VN112, 2012 VP113, and 2000 CR105. We found two sets of simultaneous near commensurabilities for these objects with a putative Planet Nine that are compatible with the current uncertainties in the objects’ orbital periods. We conducted a large number of numerical simulations of quasi-coplanar simulations (i.e. inclinations of Planet Nine and TNOs set to zero but not the giant planets) to find which values of Planet Nine’s mean anomaly and longitude of perihelion could put these objects in stable mean motion resonance (MMR) librations. We found no cases of simultaneous stable librations for multiple TNOs for more than 800 My, with most librations lasting much shorter than this time-scale. The objects 2004 VN112 and 2000 CR105 are the most unstable. Being in an MMR is not a strict requirement for long-term survival in 3D simulations, so our result cannot be used to refute Planet Nine’s existence. Nevertheless, it casts doubt and shows that theoretical attempts to constrain the position of the planet on the sky are not possible. 

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