The satellites of Uranus orbit in a low-eccentricity, equatorial plane that is tilted by 98 ° relative to the solar system—a geometry that mirrors Uranus's extreme axial tilt. Although a giant impact could have tipped Uranus, how the satellites came to share this orientation remains uncertain. Proposed formation pathways include primordial accretion followed by reorientation, formation from debris generated by the tilting impact, and reaccretion from a massive ring produced by the tidal disruption of passing bodies from the outer solar system. Current observations do not discriminate among these scenarios. Using the James Webb Space Telescope, we measured the deuterium-to-hydrogen (D/H) ratio in the water ice of the five regular satellites of Uranus. We find an average D/H ratio of 2.1 ± 0.2 × 10\u207b\u2074, nearly five times higher than that of Uranus and comparable to values measured in comets. This enrichment is inconsistent with any formation scenario in which substantial Uranian material was incorporated into the satellites, thereby excluding models that require significant mixing in an impact-derived vapor disk. The observed D/H ratios are instead compatible with models in which the satellites accreted from material that remained largely separate from Uranus, such as debris from a disrupted preexisting satellite system or from a tidally captured outer solar system body. The innermost regular satellite, Miranda, exhibits a marginally elevated D/H ratio (2.8 σ above the average of the outer satellites), potentially indicating a distinct formation history or source of water and offering an important clue for distinguishing among competing models.
", "doi": "10.1073/pnas.2519276123", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences", "publication_date": "2026-07-06", "series_number": "27", "volume": "123", "issue": "27", "pages": "e2519276123" }, { "id": "authors:r3tsk-2dp75", "collection": "authors", "collection_id": "r3tsk-2dp75", "cite_using_url": "https://authors.library.caltech.edu/records/r3tsk-2dp75", "type": "article", "title": "Structural Elucidation of N\u2082O Clusters at Low Temperatures: Exemplary Framework Stabilized by \u03c0-Hole-Driven N\u00b7\u00b7\u00b7O and N\u00b7\u00b7\u00b7N Pnicogen Bonding Interactions", "author": [ { "family_name": "Mahapatra", "given_name": "Nandalal", "orcid": "0000-0001-5976-3174", "clpid": "Mahapatra-Nandalal" }, { "family_name": "Chandra", "given_name": "Swaroop", "orcid": "0000-0002-4960-3043", "clpid": "Chandra-Swaroop" }, { "family_name": "Ramanathan", "given_name": "Nagarajan", "orcid": "0000-0002-4170-3998", "clpid": "Ramanathan-Nagarajan" }, { "family_name": "Sundararajan", "given_name": "Kalyanasundaram", "orcid": "0000-0002-9961-0030", "clpid": "Sundararajan-Kalyanasundaram" } ], "abstract": "N2O is a classic prototype, in which central nitrogen is sufficiently electropositive with a positive potential of 20 kcal mol–1 in magnitude to qualify it as a possible pnicogen. This was applied to a test with N2O clusters using ab initio calculations in association with various molecular topographic tools. The structure of the energetically dominant and N2O dimer was in favor of a perpendicular geometry, where the central nitrogen atom of the N2O submolecule assumed a near 90° angle with the adjacent N\u2550O and/or N\u2550N moiety, which provides the affirmation of central nitrogen as a possible π-hole-driven pnicogen. The terminal nitrogen and oxygen atoms of N2O continue to act as conventional electron donors (Lewis bases) with a negative potential. Overall, predominant π-hole-driven N···O and N···N pnicogen bonding interactions were observed to stabilize N2O clusters. Furthermore, N2O clusters (dimers and trimers) were synthesized at low temperatures in an Ar matrix using molecular beam (effusive and supersonic expansion) experiments. The geometries of these clusters were characterized by probing infrared spectroscopy with corroboration from ab initio computational methods. In addition to our previously investigated nitromethane and nitrobenzene systems, N2O also makes it to a pnicogen bonder’s club with the central nitrogen as a π-hole-driven pnicogen.
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