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1. Neptune Odyssey: A Flagship Concept for the Exploration of the Neptune–Triton System

   https://doi.org/10.3847/PSJ/abf654  

   Rymer, Abigail M. ; Runyon, Kirby D. ; Clyde, Brenda ; Núñez, Jorge I. ; Nikoukar, Romina ; Soderlund, Krista M. ; Sayanagi, Kunio ; Hofstadter, Mark ; Quick, Lynnae C. ; Stern, S. Alan ; et al ( September 2021 , The Planetary Science Journal)

   The Neptune Odyssey mission concept is a Flagship-class orbiter and atmospheric probe to the Neptune–Triton system. This bold mission of exploration would orbit an ice-giant planet to study the planet, its rings, small satellites, space environment, and the planet-sized moon Triton. Triton is a captured dwarf planet from the Kuiper Belt, twin of Pluto, and likely ocean world. Odyssey addresses Neptune system-level science, with equal priorities placed on Neptune, its rings, moons, space environment, and Triton. Between Uranus and Neptune, the latter is unique in providing simultaneous access to both an ice giant and a Kuiper Belt dwarf planet. The spacecraft—in a class equivalent to the NASA/ESA/ASI Cassini spacecraft—would launch by 2031 on a Space Launch System or equivalent launch vehicle and utilize a Jupiter gravity assist for a 12 yr cruise to Neptune and a 4 yr prime orbital mission; alternatively a launch after 2031 would have a 16 yr direct-to-Neptune cruise phase. Our solution provides annual launch opportunities and allows for an easy upgrade to the shorter (12 yr) cruise. Odyssey would orbit Neptune retrograde (prograde with respect to Triton), using the moon's gravity to shape the orbital tour and allow coverage of Triton, Neptune, and the space environment. The atmospheric entry probe would descend in ∼37 minutes to the 10 bar pressure level in Neptune's atmosphere just before Odyssey's orbit-insertion engine burn. Odyssey's mission would end by conducting a Cassini-like “Grand Finale,” passing inside the rings and ultimately taking a final great plunge into Neptune's atmosphere.

    

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2. TOI-5126: a hot super-Neptune and warm Neptune pair discovered by TESS and CHEOPS

   https://doi.org/10.1093/mnras/stad3036  

   Fairnington, Tyler R. ; Nabbie, Emma ; Huang, Chelsea X. ; Zhou, George ; Foo, Orion ; Millholland, Sarah ; Wright, Duncan ; Belinski, Alexandre A. ; Bieryla, Allyson ; Ciardi, David R. ; et al ( October 2023 , Monthly Notices of the Royal Astronomical Society)

   We present the confirmation of a hot super-Neptune with an exterior Neptune companion orbiting a bright (V  = 10.1 mag) F-dwarf identified by the Transiting Exoplanet Survey Satellite (TESS). The two planets, observed in sectors 45, 46, and 48 of the TESS extended mission, are $4.74_{-0.14}^{+0.16}$ and $3.86_{-0.16}^{+0.17}$ R⊕ with $5.4588385_{-0.0000072}^{+0.0000070}$ and $17.8999_{-0.0013}^{+0.0018}$ d orbital periods, respectively. We also obtained precise space-based photometric follow-up of the system with ESA’s CHaracterising ExOplanets Satellite to constrain the radius and ephemeris of TOI-5126 b. TOI-5126 b is located in the ‘hot Neptune Desert’ and is an ideal candidate for follow-up transmission spectroscopy due to its high-predicted equilibrium temperature (Teq = ${1442}_{-40}^{+46}$ K) implying a cloud-free atmosphere. TOI-5126 c is a warm Neptune (Teq = $971_{-27}^{+31}$ K) also suitable for follow-up. Tentative transit timing variations have also been identified in analysis, suggesting the presence of at least one additional planet, however this signal may be caused by spot-crossing events, necessitating further precise photometric follow-up to confirm these signals.

    

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3. Stability of H 3 O at extreme conditions and implications for the magnetic fields of Uranus and Neptune

   https://doi.org/10.1073/pnas.1921811117  

   Huang, Peihao ; Liu, Hanyu ; Lv, Jian ; Li, Quan ; Long, Chunhong ; Wang, Yanchao ; Chen, Changfeng ; Hemley, Russell J. ; Ma, Yanming ( March 2020 , Proceedings of the National Academy of Sciences)

   The anomalous nondipolar and nonaxisymmetric magnetic fields of Uranus and Neptune have long challenged conventional views of planetary dynamos. A thin-shell dynamo conjecture captures the observed phenomena but leaves unexplained the fundamental material basis and underlying mechanism. Here we report extensive quantum-mechanical calculations of polymorphism in the hydrogen–oxygen system at the pressures and temperatures of the deep interiors of these ice giant planets (to >600 GPa and 7,000 K). The results reveal the surprising stability of solid and fluid trihydrogen oxide (H 3 O) at these extreme conditions. Fluid H 3 O is metallic and calculated to be stable near the cores of Uranus and Neptune. As a convecting fluid, the material could give rise to the magnetic field consistent with the thin-shell dynamo model proposed for these planets. H 3 O could also be a major component in both solid and superionic forms in other (e.g., nonconvecting) layers. The results thus provide a materials basis for understanding the enigmatic magnetic-field anomalies and other aspects of the interiors of Uranus and Neptune. These findings have direct implications for the internal structure, composition, and dynamos of related exoplanets. 

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4. The CARMENES search for exoplanets around M dwarfs: LP 714-47 b (TOI 442.01): populating the Neptune desert

   https://doi.org/10.1051/0004-6361/202038016  

   Dreizler, S. ; Crossfield, I. J. ; Kossakowski, D. ; Plavchan, P. ; Jeffers, S. V. ; Kemmer, J. ; Luque, R. ; Espinoza, N. ; Pallé, E. ; Stassun, K. ; et al ( December 2020 , Astronomy & Astrophysics)

   We report the discovery of a Neptune-like planet (LP 714-47 b, P = 4.05204 d, m b = 30.8 ± 1.5 M ⊕ , R b = 4.7 ± 0.3 R ⊕ ) located in the “hot Neptune desert”. Confirmation of the TESS Object of Interest (TOI 442.01) was achieved with radial-velocity follow-up using CARMENES, ESPRESSO, HIRES, iSHELL, and PFS, as well as from photometric data using TESS, Spitzer , and ground-based photometry from MuSCAT2, TRAPPIST-South, MONET-South, the George Mason University telescope, the Las Cumbres Observatory Global Telescope network, the El Sauce telescope, the TÜBİTAK National Observatory, the University of Louisville Manner Telescope, and WASP-South. We also present high-spatial resolution adaptive optics imaging with the Gemini Near-Infrared Imager. The low uncertainties in the mass and radius determination place LP 714-47 b among physically well-characterised planets, allowing for a meaningful comparison with planet structure models. The host star LP 714-47 is a slowly rotating early M dwarf ( T eff = 3950 ± 51 K) with a mass of 0.59 ± 0.02 M ⊙ and a radius of 0.58 ± 0.02 R ⊙ . From long-term photometric monitoring and spectroscopic activity indicators, we determine a stellar rotation period of about 33 d. The stellar activity is also manifested as correlated noise in the radial-velocity data. In the power spectrum of the radial-velocity data, we detect a second signal with a period of 16 days in addition to the four-day signal of the planet. This could be shown to be a harmonic of the stellar rotation period or the signal of a second planet. It may be possible to tell the difference once more TESS data and radial-velocity data are obtained. 

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5. A New Dark Vortex on Neptune

   https://doi.org/10.3847/1538-3881/aaa6d6  

   Wong, Michael H. ; Tollefson, Joshua ; Hsu, Andrew I. ; Pater, Imke de ; Simon, Amy A. ; Hueso, Ricardo ; Sánchez-Lavega, Agustín ; Sromovsky, Lawrence ; Fry, Patrick ; Luszcz-Cook, Statia ; et al ( March 2018 , The Astronomical Journal)