Neptune and Triton: Essential pieces of the Solar System puzzle

Masters, A.; Achilleos, N.; Agnor, C. B.; Campagnola, Stefano; Charnoz, Sébastien; Christophe, Bruno; Coates, A. J.; Fletcher, Leigh N.; Jones, G. H.; Lamy, Laurent; Marzari, F.; Nettelmann, Nadine; Ruíz, Javier; Ambrosi, Richard M.; André, Nicolas; Bhardwaj, Anil; Fortney, Jonathan J.; Hansen, C. J.; Helled, Ravit; Moragas-Klostermeyer, G.; Orton, Glenn S.; Ray, L. C.; Reynaud, Serge; Sergis, N.; Srama, R.; Volwerk, M.

doi:10.1016/j.pss.2014.05.008

Cited by 41 publications

(33 citation statements)

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“…Working through the outlined steps [1-7] can help to better understand these two ice giants and to develop useful models for planets of similar mass and size. Given recent suggestions for new missions to Uranus and Neptune (Arridge, 2012;Masters, Adam et al, 2014) we think this is a good time to revisit important but still unexplained spacecraft based observational data such as the luminosity, as well as the interior models and their input physics that are supposed to explain them.…”

Section: Discussionmentioning

confidence: 99%

Uranus evolution models with simple thermal boundary layers

Nettelmann

Wang

Fortney

et al. 2016

Icarus

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106

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The strikingly low luminosity of Uranus (T eff ≃ T eq ) constitutes a long-standing challenge to our understanding of Ice Giant planets. Here we present the first Uranus structure and evolution models that are constructed to agree with both the observed low luminosity and the gravity field data. Our models make use of modern ab initio equations of state at high pressures for the icy components water, methane, and ammonia. Proceeding step by step, we confirm that adiabatic models yield cooling times that are too long, even when uncertainties in the ice:rock ratio (I:R) are taken into account. We then argue that the transition between the ice/rock-rich interior and the H/He-rich outer envelope should be stably stratified. Therefore, we introduce a simple thermal boundary and adjust it to reproduce the low luminosity. Due to this thermal boundary, the deep interior of the Uranus models are up to 2-3 warmer than adiabatic models, necessitating the presence of rocks in the deep interior with a possible I:R of 1× solar. Finally, we allow for an equilibrium evolution (T eff ≃ T eq ) that begun prior to the present day, which would therefore no longer require the current era to be a "special time" in Uranus' evolution. In this scenario, the thermal boundary leads to more rapid cooling of the outer envelope. When T eff ≃ T eq is reached, a shallow, subadiabatic zone in the atmosphere begins to develop. Its depth is adjusted to meet the luminosity constraint. This work provides a simple foundation for future Ice Giant structure and evolution models, that can be improved by properly treating the heat and particle fluxes in the diffusive zones.

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Section: Discussionmentioning

confidence: 99%

Uranus evolution models with simple thermal boundary layers

Nettelmann

Wang

Fortney

et al. 2016

Icarus

Self Cite

106

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“…The modest differences between the recent Uranus and present Neptune reconnection assessments do not indicate an answer to this question. The physics of both ice giant magnetosphere is likely to remain mysterious until we continue in situ spacecraft exploration, in the form of planetary orbiters [e.g., Arridge et al ., ; Masters et al ., ].…”

Section: Discussionmentioning

confidence: 99%

Magnetic reconnection at Neptune's magnetopause

Masters

2015

JGR Space Physics

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What we know about the magnetosphere of the outermost planet, Neptune, is primarily based on data taken during the Voyager 2 flyby in 1989. Establishing how Neptune's magnetosphere interacts with the solar wind is crucial for understanding the dynamics of the system. Here we assess how magnetic reconnection couples the solar wind to Neptune's magnetosphere, using analytical modeling that was recently applied to the case of Uranus. The modeling suggests that typical near-Neptune solar wind parameters make conditions at Neptune's magnetopause less favorable for magnetic reconnection than at the magnetopause boundary of any other solar system magnetosphere. The location of reconnection sites on Neptune's magnetopause is expected to be highly sensitive to planetary longitude and season, as well as interplanetary magnetic field (IMF) orientation, which is similar to the situation at Uranus. Also similar to past Uranus results, the present Neptune modeling indicates a seasonal effect, where one of the two dominant (Parker spiral) IMF orientations produces more favorable conditions for magnetopause reconnection than the other near equinox. We estimate the upper limit of the reconnection voltage applied to Neptune's magnetosphere as 35 kV (the typical voltage is expected to be considerably lower). Further progress in understanding the solar wind-magnetosphere interaction at Neptune requires other coupling mechanisms to be considered, as well as how reconnection operates at high plasma β.

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“…Compared to the other outer planets, Neptune's magnetosphere was found to be relatively empty [ Belcher et al , ] although Triton, with its atmosphere [ Broadfoot et al , ], may act as a source [ Richardson et al , ; Zhang et al , ]. However, the role of Triton as a plasma source in Neptune's magnetosphere is ultimately not yet known [ Masters et al , ].…”

Section: Introductionmentioning

confidence: 99%

Global MHD simulations of Neptune's magnetosphere

et al. 2016

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A global magnetohydrodynamic (MHD) simulation has been performed in order to investigate the outer boundaries of Neptune's magnetosphere at the time of Voyager 2's flyby in 1989 and to better understand the dynamics of magnetospheres formed by highly inclined planetary dipoles. Using the MHD code Gorgon, we have implemented a precessing dipole to mimic Neptune's tilted magnetic field and rotation axes. By using the solar wind parameters measured by Voyager 2, the simulation is verified by finding good agreement with Voyager 2 magnetometer observations. Overall, there is a large‐scale reconfiguration of magnetic topology and plasma distribution. During the “pole‐on” magnetospheric configuration, there only exists one tail current sheet, contained between a rarefied lobe region which extends outward from the dayside cusp, and a lobe region attached to the nightside cusp. It is found that the tail current always closes to the magnetopause current system, rather than closing in on itself, as suggested by other models. The bow shock position and shape is found to be dependent on Neptune's daily rotation, with maximum standoff being during the pole‐on case. Reconnection is found on the magnetopause but is highly modulated by the interplanetary magnetic field (IMF) and time of day, turning “off” and “on” when the magnetic shear between the IMF and planetary fields is large enough. The simulation shows that the most likely location for reconnection to occur during Voyager 2's flyby was far from the spacecraft trajectory, which may explain the relative lack of associated signatures in the observations.

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Neptune and Triton: Essential pieces of the Solar System puzzle

Cited by 41 publications

References 100 publications

Uranus evolution models with simple thermal boundary layers

Uranus evolution models with simple thermal boundary layers

Magnetic reconnection at Neptune's magnetopause

Global MHD simulations of Neptune's magnetosphere

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