The measured compositions of Uranus and Neptune from their formation on the CO ice line

Journal Article · Sat Sep 20 04:00:00 EDT 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/793/1/9· OSTI ID:22365054

Ali-Dib, Mohamad; Mousis, Olivier; Petit, Jean-Marc ^[1]

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1. Institut UTINAM, CNRS/INSU, Université de Franche-Comté, UMR 6213, Observatoire de Besançon, BP 1615, F-25010 Besançon Cedex (France)

The formation mechanisms of the ice giants Uranus and Neptune, and the origin of their elemental and isotopic compositions, have long been debated. The density of solids in the outer protosolar nebula is too low to explain their formation, and spectroscopic observations show that both planets are highly enriched in carbon, very poor in nitrogen, and the ices from which they originally formed might have had deuterium-to-hydrogen ratios lower than the predicted cometary value, unexplained properties that were observed in no other planets. Here, we show that all these properties can be explained naturally if Uranus and Neptune both formed at the carbon monoxide ice line. Due to the diffusive redistribution of vapors, this outer region of the protosolar nebula intrinsically has enough surface density to form both planets from carbon-rich solids but nitrogen-depleted gas, in abundances consistent with their observed values. Water-rich interiors originating mostly from transformed CO ices reconcile the D/H value of Uranus's and Neptune's building blocks with the cometary value. Finally, our scenario generalizes a well known hypothesis that Jupiter formed on an ice line (water snow line) for the two ice giants, and might be a first step toward generalizing this mechanism for other giant planets.

• OSTI ID: 22365054
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 793; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CARBON
CARBON MONOXIDE
DENSITY
DEUTERIUM
ELEMENT ABUNDANCE
HYDROGEN
HYPOTHESIS
ICE
ISOTOPE RATIO
JUPITER PLANET
NEPTUNE PLANET
NITROGEN
PROTOPLANETS
SATELLITE ATMOSPHERES
SATELLITES
SURFACES
URANUS PLANET
VAPORS
WATER