Compositions and Interior Structures of the Large Moons of Uranus and Implications for Future Spacecraft Observations

Castillo‐Rogez, Julie; Weiss, B. P.; Beddingfield, C. B.; Biersteker, John B.; Cartwright, Richard; Goode, Allison; Daswani, Mohit Melwani; Neveu, Marc

doi:10.1029/2022je007432

Cited by 25 publications

(46 citation statements)

References 199 publications

(355 reference statements)

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“…Nitrogen has been detected on planets, icy satellites, and small bodies across the solar system, yet confirmation of N-bearing species has been challenging due to the faintness of the Uranian moons and the prevalence of stronger absorbers such as H 2 O ice, dark material, and CO 2 ice. Nevertheless, the presence of nitrogen on the Uranian moons would have important implications for their internal states, thermal evolutions, and activity, at present or in the past (Beddingfield et al 2022a(Beddingfield et al , 2022bCastillo-Rogez et al 2023).…”

Section: Implications For Umbriel's Surface Chemistry and Geochemistrymentioning

confidence: 99%

“…The larger outer moons Titania and Oberon may have long-lived internal oceans sustained by radiogenic heating (Bierson & Nimmo 2022) that hypothetically could have spurred the exposure or emplacement of ocean-derived material rich in NH 3 in the past. Although Umbriel may have a residual ocean (Castillo-Rogez et al 2023), it has one of the most ancient icy satellite surfaces in the solar system ( -+ 4.5 0.2 0.0  Ga, Kirchoff et al 2022) and displays little evidence for endogenic activity. The presence of the 2.2 μm bands in spectra of Umbriel, and other absorption features between 2.12 and 2.27 μm, raises important questions about the nature of the species that are contributing to its spectral properties, and whether NH 3 -and other N-bearing species are present.…”

Section: Introductionmentioning

confidence: 99%

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Evidence for Nitrogen-bearing Species on Umbriel: Sourced from a Subsurface Ocean, Undifferentiated Crust, or Impactors?

Cartwright¹,

DeColibus²,

Castillo‐Rogez³

et al. 2023

Planet. Sci. J.

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Near-infrared spectra of Umbriel and the other classical Uranian moons exhibit 2.2 μm absorption bands that could result from ammonia (NH3) bearing species, possibly exposed in the geologically recent past. However, Umbriel has an ancient surface with minimal evidence for recent endogenic activity, raising the possibility that more refractory species are present, and/or that NH3 is retained over long timescales. We analyzed 33 spectra of Umbriel to investigate its 2.2 μm band, along with three other absorption features we identified near 2.14, 2.22, and 2.24 μm. We assessed the subobserver longitudinal distributions of these four bands, finding that they are present across Umbriel and may be spatially associated with geologic features such as craters and large basins. We compared the bands to 15 candidate constituents. We found that Umbriel’s 2.14 μm and 2.22 μm bands are most consistent with the spectral signature of organics, its 2.24 μm band is best matched by NH3 ice, and its 2.2 μm band is consistent with the signatures of NH3–H2O mixtures, aluminum-bearing phyllosilicates, and sodium-bearing carbonates. However, some of these candidate constituents do not match Umbriel’s spectral properties in other wavelength regions, highlighting the gaps in our understanding of the Uranian moons’ surface compositions. Umbriel’s 2.14 μm band may alternatively result from a 2ν 3 overtone mode of CO2 ice. If present on Umbriel, these candidate constituents could have formed in contact with an internal ocean and were subsequently exposed during Umbriel’s early history. Alternatively, these constituents might have originated in an undifferentiated crust or were delivered by impactors.

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Section: Implications For Umbriel's Surface Chemistry and Geochemistrymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Evidence for Nitrogen-bearing Species on Umbriel: Sourced from a Subsurface Ocean, Undifferentiated Crust, or Impactors?

Cartwright¹,

DeColibus²,

Castillo‐Rogez³

et al. 2023

Planet. Sci. J.

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“…NH 3 can also increase the electrical conductivity of salty oceans (Castillo-Rogez et al 2022a). Consequently, the presence of NH 3 and other NH-bearing species can have important implications for the internal properties of icy bodies, including the longevity and thicknesses of subsurface oceans (e.g., Castillo-Rogez et al 2022b).…”

Section: The Effects Of Porositymentioning

confidence: 99%

Tethys’s Heat Fluxes Varied with Time in the Ithaca Chasma and Telemus Basin Region

et al. 2023

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We investigated how lithospheric heat fluxes varied temporally and spatially on the Saturnian moon Tethys, focusing on the region of Ithaca Chasma that overprints Telemus Impact Basin. Our results, derived from flexure associated with Ithaca, indicate elastic thicknesses of 4.1 ± 0.3 km to 6.4 ± 0.4 km and heat fluxes ranging from 12 to 39 mW m−2 assuming a nonporous pure H2O ice lithosphere. Our results for Ithaca’s south limb are similar to previous estimates within the north limb, indicating consistent heat fluxes across a large spatial extent in this area. However, our estimates are lower than those for the older Telemus Basin (>60 mW m−2), revealing evidence that Tethys experienced a substantial temporal variation in heat fluxes in this region. Heat fluxes reflected by Ithaca are similar to previous estimates for Tethys’s two youngest impact basins, Melanthius and Odysseus, suggesting that Ithaca may also be relatively young. If Tethys’s lithosphere is porous, then our heat flux estimates for Ithaca Chasma drop to 12–38 mW m−2, 11–35 mW m−2, and 10–33 mW m−2 for 5%, 15%, and 25% porosities, respectively. If Tethys’s lithosphere includes ∼10% NH3-hydrates, then the estimates are 5–16 mW m−2, 5–15 mW m−2, 4–14 mW m−2, and 4–13 mW m−2 for 0%, 5%, 15%, and 25% porosities, respectively. Although we find that some ground-based reflectance spectra hint at 2.2 μm bands that may result from NH3-bearing species, the detected features are weak and may not result from surface constituents. Consequently, our heat flux estimates that assume a pure H2O ice lithosphere are likely more accurate.

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“…The answer relies on our understanding of the chemical and thermal evolution of subsurface oceans (Hendrix et al 2018). In addition to the ocean world poster children-Europa, Ganymede, Titan, and Enceladus-there may be many more ocean worlds in the outer solar system: the Uranian moons and Pluto, to name a few (e.g., Hendrix et al 2018); however, the lack of tidal heating in these objects may severely limit their prospect for hosting liquid at present (e.g., Bierson & Nimmo 2022;Castillo-Rogez et al 2023). An important control on ocean evolution is the composition of the ice shell, specifically the presence and abundance of clathrate hydrates (crystalline cages of water molecules surrounding a gas molecule, also called gas hydrates; e.g., Castillo-Rogez et al 2019;Kamata et al 2019;Kalousová & Sotin 2020).…”

Section: Introductionmentioning

confidence: 99%

Timing and Abundance of Clathrate Formation Control Ocean Evolution in Outer Solar System Bodies: Challenges of Maintaining a Thick Ocean within Pluto

Courville,

Castillo-Rogez,

Daswani

et al. 2023

Planet. Sci. J.

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Clathrate hydrates may represent a sizable fraction of material within the icy shells of Kuiper Belt objects and icy moons. They influence the chemical and thermal evolution of subsurface oceans by locking volatiles into the ice shell and by providing more thermal insulation than pure water ice. We model the formation of these crystalline compounds in conditions relevant to outer solar system objects, using Pluto as an example. Although Pluto may have hosted a thick ocean in its early history, Pluto’s overall heat budget is probably insufficient to preserve liquid today if its outer shell is pure water ice. One previously proposed reconciliation is that Pluto’s ocean has a winter jacket: an insulating layer of methane clathrate hydrates. Unfortunately, assessments of the timing, quantity, and type of clathrate hydrates forming within planetary bodies are lacking. Our work quantifies the abundance of clathrate-forming gases present in Pluto’s ocean from accreted ices and volatiles released during thermal metamorphism throughout Pluto’s history. We find that if Pluto formed with the same relative abundances of ices found in comets, then a buoyant layer of mixed methane and carbon dioxide clathrate hydrates may form above Pluto’s ocean, though we find it insufficient to preserve a thick ocean today. In general, our study provides methodology for predicting clathrate formation in ocean worlds, which is necessary to predict the evolution of the ocean’s composition and whether a liquid layer remains at present.

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Compositions and Interior Structures of the Large Moons of Uranus and Implications for Future Spacecraft Observations

Cited by 25 publications

References 199 publications

Evidence for Nitrogen-bearing Species on Umbriel: Sourced from a Subsurface Ocean, Undifferentiated Crust, or Impactors?

Evidence for Nitrogen-bearing Species on Umbriel: Sourced from a Subsurface Ocean, Undifferentiated Crust, or Impactors?

Tethys’s Heat Fluxes Varied with Time in the Ithaca Chasma and Telemus Basin Region

Timing and Abundance of Clathrate Formation Control Ocean Evolution in Outer Solar System Bodies: Challenges of Maintaining a Thick Ocean within Pluto

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