Interior and Gravity Field Models for Uranus Suggest a Mixed-composition Interior: Implications for the Uranus Orbiter and Probe
The interior composition and structure of Uranus are ambiguous. It is unclear whether Uranus is composed of fully differentiated layers dominated by an icy mantle or has smooth compositional gradients. The Uranus Orbiter and Probe (UOP), the next NASA flagship mission prioritized by the Planetary Sc...
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2025-01-01
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| Series: | The Planetary Science Journal |
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| Online Access: | https://doi.org/10.3847/PSJ/ada124 |
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| author | Zifan Lin Sara Seager Benjamin P. Weiss |
| author_facet | Zifan Lin Sara Seager Benjamin P. Weiss |
| author_sort | Zifan Lin |
| collection | DOAJ |
| description | The interior composition and structure of Uranus are ambiguous. It is unclear whether Uranus is composed of fully differentiated layers dominated by an icy mantle or has smooth compositional gradients. The Uranus Orbiter and Probe (UOP), the next NASA flagship mission prioritized by the Planetary Science and Astrobiology Survey 2023–2032, will constrain the planet's interior by measuring its gravity and magnetic fields. To characterize the Uranian interior, here we present CORGI , a newly developed planetary interior and gravity model. We confirm that high degrees of mixing are required for Uranus interior models to be consistent with the J _2 and J _4 gravity harmonics measured by Voyager 2. Empirical models, which have smooth density profiles that require extensive mixing, can reproduce the Voyager 2 measurements. Distinct-layer models with mantles composed of H _2 O–H/He or H _2 O–CH _4 –NH _3 mixtures are consistent with the Voyager 2 measurements if the heavy element mass fraction, Z , in the mantle ≲85%, or if atmospheric Z ≳ 25%. Our gravity harmonics model shows that UOP J _2 and J _4 measurements can distinguish between high ( Z ≥ 25%) and low ( Z = 12.5%) atmospheric metallicity scenarios. The UOP can robustly constrain J _6 and potentially J _8 given polar orbits within rings. An ice-rich composition can naturally explain the source of Uranus’s magnetic field. However, because the physical properties of rock–ice mixtures are poorly known, magnetic field generation by a rock-rich composition cannot be ruled out. Future experiments and simulations on realistic planetary building materials will be essential for refining Uranus interior models. |
| format | Article |
| id | doaj-art-99e1678a3a1a471dbe6f53e90b5594ef |
| institution | Kabale University |
| issn | 2632-3338 |
| language | English |
| publishDate | 2025-01-01 |
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| series | The Planetary Science Journal |
| spelling | doaj-art-99e1678a3a1a471dbe6f53e90b5594ef2025-01-30T10:26:13ZengIOP PublishingThe Planetary Science Journal2632-33382025-01-01622710.3847/PSJ/ada124Interior and Gravity Field Models for Uranus Suggest a Mixed-composition Interior: Implications for the Uranus Orbiter and ProbeZifan Lin0https://orcid.org/0000-0003-0525-9647Sara Seager1https://orcid.org/0000-0002-6892-6948Benjamin P. Weiss2https://orcid.org/0000-0003-3113-3415Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, MA 02139, USA ; zifanlin@mit.eduDepartment of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, MA 02139, USA ; zifanlin@mit.edu; Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology , Cambridge, MA 02139, USA; Department of Aeronautics and Astronautics, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, MA 02139, USADepartment of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, MA 02139, USA ; zifanlin@mit.eduThe interior composition and structure of Uranus are ambiguous. It is unclear whether Uranus is composed of fully differentiated layers dominated by an icy mantle or has smooth compositional gradients. The Uranus Orbiter and Probe (UOP), the next NASA flagship mission prioritized by the Planetary Science and Astrobiology Survey 2023–2032, will constrain the planet's interior by measuring its gravity and magnetic fields. To characterize the Uranian interior, here we present CORGI , a newly developed planetary interior and gravity model. We confirm that high degrees of mixing are required for Uranus interior models to be consistent with the J _2 and J _4 gravity harmonics measured by Voyager 2. Empirical models, which have smooth density profiles that require extensive mixing, can reproduce the Voyager 2 measurements. Distinct-layer models with mantles composed of H _2 O–H/He or H _2 O–CH _4 –NH _3 mixtures are consistent with the Voyager 2 measurements if the heavy element mass fraction, Z , in the mantle ≲85%, or if atmospheric Z ≳ 25%. Our gravity harmonics model shows that UOP J _2 and J _4 measurements can distinguish between high ( Z ≥ 25%) and low ( Z = 12.5%) atmospheric metallicity scenarios. The UOP can robustly constrain J _6 and potentially J _8 given polar orbits within rings. An ice-rich composition can naturally explain the source of Uranus’s magnetic field. However, because the physical properties of rock–ice mixtures are poorly known, magnetic field generation by a rock-rich composition cannot be ruled out. Future experiments and simulations on realistic planetary building materials will be essential for refining Uranus interior models.https://doi.org/10.3847/PSJ/ada124Planetary interiorSolar system planetsUranus |
| spellingShingle | Zifan Lin Sara Seager Benjamin P. Weiss Interior and Gravity Field Models for Uranus Suggest a Mixed-composition Interior: Implications for the Uranus Orbiter and Probe The Planetary Science Journal Planetary interior Solar system planets Uranus |
| title | Interior and Gravity Field Models for Uranus Suggest a Mixed-composition Interior: Implications for the Uranus Orbiter and Probe |
| title_full | Interior and Gravity Field Models for Uranus Suggest a Mixed-composition Interior: Implications for the Uranus Orbiter and Probe |
| title_fullStr | Interior and Gravity Field Models for Uranus Suggest a Mixed-composition Interior: Implications for the Uranus Orbiter and Probe |
| title_full_unstemmed | Interior and Gravity Field Models for Uranus Suggest a Mixed-composition Interior: Implications for the Uranus Orbiter and Probe |
| title_short | Interior and Gravity Field Models for Uranus Suggest a Mixed-composition Interior: Implications for the Uranus Orbiter and Probe |
| title_sort | interior and gravity field models for uranus suggest a mixed composition interior implications for the uranus orbiter and probe |
| topic | Planetary interior Solar system planets Uranus |
| url | https://doi.org/10.3847/PSJ/ada124 |
| work_keys_str_mv | AT zifanlin interiorandgravityfieldmodelsforuranussuggestamixedcompositioninteriorimplicationsfortheuranusorbiterandprobe AT saraseager interiorandgravityfieldmodelsforuranussuggestamixedcompositioninteriorimplicationsfortheuranusorbiterandprobe AT benjaminpweiss interiorandgravityfieldmodelsforuranussuggestamixedcompositioninteriorimplicationsfortheuranusorbiterandprobe |