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1. Cometary Activity Discovered on Vacationing Centaur 2019 OE31

   https://doi.org/10.3847/2515-5172/ad14f5  

   Oldroyd, William J.; Chandler, Colin Orion; Trujillo, Chadwick A.; Deen, Sam; Hsieh, Henry H.; Farrell, Kennedy A.; DeSpain, Jarod A.; Kueny, Jay K.; Burris, William A.; Sheppard, Scott S.; et al (December 2023, Research Notes of the AAS)

   Abstract We have detected cometary activity on minor planet 2019 OE₃₁through both theActive AsteroidsCitizen Science program and an independent archival search. Before 2013, 2019 OE₃₁was on a Centaur orbit, between the orbits of Jupiter and Neptune. Centaurs are objects in transition from the outer solar system to the inner solar system. They play a vital role in the understanding of the Kuiper Belt and comets. In 2013 October, following a close encounter with Jupiter, 2019 OE₃₁moved to an orbit entirely interior to that of Jupiter. This reduced orbital distance and, hence, increased temperature is likely the cause of the observed activity. Through a suite of orbital dynamics simulations, we find that 2019 OE₃₁will experience many more similar encounters and is statistically likely to return to a Centaur orbit, potentially within the next 80 yr, from its current “vacation.” 

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2. An In-depth Look at TOI-3884b: A Super-Neptune Transiting an M4Dwarf with Persistent Starspot Crossings

   https://doi.org/10.3847/1538-3881/accc2f  

   Libby-Roberts, Jessica_E; Schutte, Maria; Hebb, Leslie; Kanodia, Shubham; Cañas, Caleb_I; Stefánsson, Guðmundur; Lin, Andrea_S_J; Mahadevan, Suvrath; Partstheythem, Winter; Powers, Luke; et al (May 2023, The Astronomical Journal)

   Abstract We perform an in-depth analysis of the recently validated TOI-3884 system, an M4-dwarf star with a transiting super-Neptune. Using high-precision light curves obtained with the 3.5 m Apache Point Observatory and radial velocity observations with the Habitable-zone Planet Finder, we derive a planetary mass of ${32.6}_{-7.4}^{+7.3}{M}_{\oplus }$and radius of 6.4 ± 0.2R_⊕. We detect a distinct starspot crossing event occurring just after ingress and spanning half the transit for every transit. We determine this spot feature to be wavelength dependent with the amplitude and duration evolving slightly over time. Best-fit starspot models show that TOI-3884b possesses a misaligned (λ= 75° ± 10°) orbit that crosses a giant pole spot. This system presents a rare opportunity for studies into the nature of both a misaligned super-Neptune and spot evolution on an active mid-M dwarf. 

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3. The Promise and Limitations of Precision Gravity: Application to the Interior Structure of Uranus and Neptune

   https://doi.org/10.3847/PSJ/ac60ff  

   Movshovitz, Naor; Fortney, Jonathan J. (April 2022, The Planetary Science Journal)

   Abstract We study the constraining power of a high-precision measurement of the gravity field for Uranus and Neptune, as could be delivered by a low-periapse orbiter. Our study is practical, assessing the possible deliverables and limitations of such a mission with respect to the structure of the planets. Our study is also academic, assessing in a general way the relative importance of the low-order gravity, high-order gravity, rotation rate, and moment of inertia (MOI) in constraining planetary structure. We attempt to explore all possible interior density structures of a planet that are consistent with hypothetical gravity data via MCMC sampling of parameterized density profiles. When the gravity field is poorly known, as it is today, uncertainties in the rotation rate on the order of 10 minutes are unimportant, as they are interchangeable with uncertainties in the gravity coefficients. By the same token, when the gravity field is precisely determined, the rotation rate must be known to comparable precision. When gravity and rotation are well known, the MOI becomes well constrained, limiting the usefulness of independent MOI determinations unless they are extraordinarily precise. For Uranus and Neptune, density profiles can be well constrained. However, the nonuniqueness of the relative roles of H/He, watery volatiles, and rock in the deep interior will still persist with high-precision gravity data. Nevertheless, the locations and magnitudes (in pressure space) of any large-scale composition gradient regions can likely be identified, offering a crucially better picture of the interiors of Uranus or Neptune. 

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4. Can the Gravitational Effect of Planet X be Detected in Current-era Tracking of the Known Major and Minor Planets?

   https://doi.org/10.3847/PSJ/acc7a2  

   Gomes, Daniel C. H.; Murray, Zachary; Gomes, Rafael C. H.; Holman, Matthew J.; Bernstein, Gary M. (April 2023, The Planetary Science Journal)

   Abstract Using Fisher information matrices, we forecast the uncertaintiesσ_Mon the measurement of a “Planet X” at heliocentric distanced_Xvia its tidal gravitational field’s action on the known planets. Using planetary measurements currently in hand, including ranging from the Juno, Cassini, and Mars-orbiting spacecraft, we forecast a median uncertainty (over all sky positions) of ${\sigma }_M=0.22M_{\oplus }{\left(d_x/400\mathrm{au}\right)}^3.$A 5σdetection of a 5M_⊕Planet X atd_X= 400 au should be possible over the full sky but over only 5% of the sky atd_X= 800 au. The gravity of an undiscovered Earth- or Mars-mass object should be detectable over 90% of the sky to a distance of 260 or 120 au, respectively. Upcoming Mars ranging improves these limits only slightly. We also investigate the power of high-precision astrometry of ≈8000 Jovian Trojans over the 2023–2035 period from the upcoming Legacy Survey of Space and Time (LSST). We find that the dominant systematic errors in optical Trojan astrometry (photocenter motion, nongravitational forces, and differential chromatic refraction) can be solved internally with minimal loss of information. The Trojan data allow cross-checks with Juno/Cassini/Mars ranging, but do not significantly improve the best achievableσ_Mvalues until they are ≳10× more accurate than expected from LSST. The ultimate limiting factor in searches for a Planet X tidal field is confusion with the tidal field created by the fluctuating quadrupole moment of the Kuiper Belt as its members orbit. This background will not, however, become the dominant source of uncertainty until the data get substantially better than they are today. 

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5. The TESS-Keck Survey. XXII. A Sub-Neptune Orbiting TOI-1437

   https://doi.org/10.3847/1538-3881/ad6901  

   Pidhorodetska, Daria; Gilbert, Emily_A; Kane, Stephen_R; Barclay, Thomas; Polanski, Alex_S; Hill, Michelle_L; Stassun, Keivan_G; Giacalone, Steven; Ciardi, David_R; Boyle, Andrew_W; et al (August 2024, The Astronomical Journal)

   Abstract Exoplanet discoveries have revealed a dramatic diversity of planet sizes across a vast array of orbital architectures. Sub-Neptunes are of particular interest; due to their absence in our own solar system, we rely on demographics of exoplanets to better understand their bulk composition and formation scenarios. Here, we present the discovery and characterization of TOI-1437 b, a sub-Neptune with a 18.84 day orbit around a near-solar analog (M_⋆= 1.10 ± 0.10M_☉,R_⋆=1.17 ± 0.12R_☉). The planet was detected using photometric data from the Transiting Exoplanet Survey Satellite (TESS) mission and radial velocity (RV) follow-up observations were carried out as a part of the TESS-Keck Survey using both the HIRES instrument at Keck Observatory and the Levy Spectrograph on the Automated Planet Finder telescope. A combined analysis of these data reveal a planet radius ofR_p= 2.24 ± 0.23R_⊕and a mass measurement ofM_p= 9.6 ± 3.9M_⊕). TOI-1437 b is one of few (∼50) known transiting sub-Neptunes orbiting a solar-mass star that has a RV mass measurement. As the formation pathway of these worlds remains an unanswered question, the precise mass characterization of TOI-1437 b may provide further insight into this class of planet. 

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