Direct evidence of multiple reservoirs of volatile nitrogen in a protosolar nebula analogue

Abstract

Isotopic ratios are keys to understanding the origin and early evolution of the solar system in the context of Galactic nucleosynthesis. The large range of measured 14 N/ 15 N isotopic ratios in the solar system reflects distinct reservoirs of nitrogen whose origins remain to be determined. We have directly measured a C 14 N/C 15 N abundance ratio of 323 ± 30 in the disk orbiting the nearby young star TW Hya. This value, which is in good agreement with nitrogen isotopic ratios measured for prestellar cores, likely reflects the primary present-day reservoir of nitrogen in the solar neighbourhood. These results support models invoking novae as primary 15 N sources as well as outward migration of the Sun over its lifetime, and suggest that comets sampled a secondary, 15 N-rich reservoir during solar system formation.

The Peculiar Volatile Composition of CO-dominated Comet C/2016 R2 (PanSTARRS)

“…There are not many measurements of the NH 3 /N 2 value in comets; however, this limit for R2 PanSTARRS is much lower than measured for comet Halley (∼1000%), and is closer to derived values for several dense molecular clouds in star-forming regions (∼0.6%) (Womack et al 1992). The very low derived relative abundance of NH 3 /N 2 is consistent with the suggestion by Wierzchos and Womack (2018) that R2 PanSTARRS formed in an environment with decreased photodissociation of N 2 , leading to preserving, or shielding, of N 2 and inhibited production pathways of hydrogen-rich species, such as HCN and NH 3 (Hily-Blant et al 2017).…”

No nitrogen fractionation on 600 au scale in the Sun progenitor analogue OMC–2 FIR4

“…They derived the same R value, ∼270, in all the five molecules, regardless on the CN-or NH-bond. This measured value is slightly lower than the most recent estimate in the interstellar medium nowadays (375±60, Colzi et al 2018a), although measurements in the local ISM show a large spread of values (Hily-Blant et al 2017 and reference therein). However, these single-dish measurements provide average values over ∼10000 au, namely on the whole protocluster, so that it cannot be excluded the presence of local spots enriched (or depleted) in 15 N. In fact, differences of a factor 2 on R can be measured from N 2 H + when R is measured on angular scales that can resolve the dense cores from the extended, diffuse envelope, as found by Colzi et al (2019) in a high-mass protocluster.…”

Cometary Chemistry and the Origin of Icy Solar System Bodies: The View AfterRosetta

“…For 14 N/ 15 N in HCN, CN, and NH2 there are large enrichments in 15 N (up to a factor of 3) relative to solar (Bockelée-Morvan et al 2015, and references therein). This is explained by two different reservoirs, one for atomic nitrogen and the other for molecular nitrogen (Hily-Blant et al, 2017). N2 has so far only been detected in the coma of 67P/CG (Rubin et al 2015) and as ion N2 + in a few other comets (e.g.…”