The science case for an orbital mission to Uranus: Exploring the origins and evolution of ice giant planets

Arridge, C. S.; Achilleos, N.; Agarwal, Jessica; Agnor, C. B.; Ambrosi, Richard M.; André, Nicolas; Badman, S. V.; Baines, K. H.; Banfield, D.; Barthélemy, Mathieu; Bisi, M. M.; Blum, Jürgen; Bocanegra-Bahamón, Tatiana; Bonfond, Bertrand; Bracken, Colm; Brandt, P. C.; Briand, Cyril; Briois, C.; Brooks, S. M.; Castillo‐Rogez, Julie; Cavalié, T.; Christophe, Bruno; Coates, A. J.; Collinson, G.; Cooper, J. F.; Costa-Sitja, M.; Courtin, R.; Daglis, Ioannis A.; Pater, Imke de; Desai, M. I.; Dirkx, Dominic; Dougherty, M. K.; Ebert, R. W.; Filacchione, G.; Fletcher, Leigh N.; Fortney, Jonathan J.; Gerth, I.; Grassi, D.; Grodent, Denis; Grün, E.; Gustin, Jacques; Hedman, M. M.; Helled, Ravit; Henri, Pierre; Hess, S.; Hillier, Jon K.; Hofstadter, Mark; Holme, Richard; Horányi, M.; Hospodarsky, G. B.; Hsu, Sean; Irwin, Patrick; Jackman, C. M.; Karatekin, Özgür; Kempf, S.; Khalisi, Emil; Konstantinidis, Kostas; Krüger, Harald; Kurth, W. S.; Labrianidis, C.; Lainey, V.; Lamy, Laurent; Laneuville, M.; Lucchesi, David M.; Luntzer, A.; MacArthur, J. L.; Maier, Andrea; Masters, A.; McKenna‐Lawlor, S.; Melin, Henrik; Milillo, A.; Moragas-Klostermeyer, G.; Morschhauser, A.; Moses, J. I.; Mousis, O.; Nettelmann, Nadine; Neubauer, F. M.; Nordheim, Tom; Noyelles, Benoît; Orton, G. S.; Owens, M. J.; Peron, Roberto; Plainaki, C.; Postberg, F.; Rambaux, N.; Retherford, Kurt D.; Reynaud, Serge; Roussos, E.; Russell, C. T.; Rymer, A. M.; Sallantin, R.; Sánchez‐Lavega, A.; Santolı́k, O.; Saur, Joachim; Sayanagi, Kunio M.; Schenk, P.; Schubert, J.; Sergis, N.; Sittler, E. C.; Smith, A. W.; Spahn, F.; Srama, R.; Stallard, T.; Sterken, Veerle; Sternovsky, Z.; Tiscareno, Matthew S.; Tobie, G.; Tosi, F.; Trieloff, M.; Turrini, D.; Turtle, E. P.; Vinatier, S.; Wilson, R.; Zarka, Philippe

doi:10.1016/j.pss.2014.08.009

Cited by 59 publications

(55 citation statements)

References 128 publications

(141 reference statements)

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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, 2014;Masters et al, 2014].…”

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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Section: Discussionmentioning

confidence: 99%

Magnetic reconnection at Neptune's magnetopause

Masters

2015

JGR Space Physics

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“…This is shown more specifically in Schulz et al [1995], who note that it is not fully self consistent as their model does not achieve thermodynamic equilibrium. Although there have been science cases put forward for new missions to visit both Uranus [Arridge et al, 2014] and Neptune [Agnor et al, 2009;Hansen et al, 2009;Christophe et al, 2012;, in situ observational data for the foreseeable future remain limited to the Voyager 2 data set. Computer simulation offers an alternative approach to experimental measurements and can be useful in providing more insight into Neptune's magnetosphere and complement existing models and observations.…”

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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“…Exoplanets observations have showed that Super Earths to Neptune-mass planets are the most common in the galaxy. A dedicated Uranus & Neptune mission (Arridge et al 2012(Arridge et al , 2014 will hence shed light on not only the history of our solar system, but also the formation of exoplanets. Fig.…”

Section: Discussionmentioning

confidence: 99%

What is Neptune's D/H ratio really telling us about its water abundance?

Ali-Dib

Lakhlani

2018

Monthly Notices of the Royal Astronomical Society

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We investigate the deep water abundance of Neptune using a simple 2-component (core + envelope) toy model. The free parameters of the model are the total mass of heavy elements in the planet (Z), the mass fraction of Z in the envelope (f env ), and the D/H ratio of the accreted building blocks (D/H build ). We systematically search the allowed parameter space on a grid and constrain it using Neptune's bulk carbon abundance, D/H ratio, and interior structure models. Assuming solar C/O ratio and cometary D/H for the accreted building blocks forming the planet, we can fit all of the constraints if less than ∼ 15% of Z is in the envelope (f median env ∼ 7%), and the rest is locked in a solid core. This model predicts a maximum bulk oxygen abundance in Neptune of 65× solar value. If we assume a C/O of 0.17, corresponding to clathratehydrates building blocks, we predict a maximum oxygen abundance of 200× solar value with a median value of ∼ 140. Thus, both cases lead to an oxygen abundance significantly lower than the preferred value of Cavalié et al. (2017) (∼ 540 × solar), inferred from model dependent deep CO observations. Such high water abundances are excluded by our simple but robust model. We attribute this discrepancy to our imperfect understanding of either the interior structure of Neptune or the chemistry of the primordial protosolar nebula.

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The science case for an orbital mission to Uranus: Exploring the origins and evolution of ice giant planets

Cited by 59 publications

References 128 publications

Magnetic reconnection at Neptune's magnetopause

Magnetic reconnection at Neptune's magnetopause

Global MHD simulations of Neptune's magnetosphere

What is Neptune's D/H ratio really telling us about its water abundance?

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