Stable isotopic ratios such as the ratio of the two stable nitrogen isotopes, 14N/15N, represent unique probes for tracing the origin and evolution of the building blocks of planets and minor bodies in a stellar system, provided their fractionation mechanisms are well understood. Since no planetary system can be investigated in greater detail than our solar system, stable isotopic ratios are also an invaluable tool for linking the properties and composition of the solar system bodies to the physical and chemical processes observed in star-forming regions.
The solar system features a peculiar enrichment in rare nitrogen-15 in the terrestrial planets, cometary ices, and certain meteoritic inclusions with respect to the solar composition. The origin of this nitrogen isotopic anomaly is still unclear.
Existing measurements of the 14N/15N ratio in prestellar cores, around protostars, and in protoplanetary disks seem to be best explained by an isotope-selective photochemistry scenario with two different nitrogen isotopic reservoirs, linked to molecular nitrogen and atomic nitrogen.
We will present measurements of the 14N/15N ratio in comet 67P/Churyumov?Gerasimenko by the ROSINA instrument onboard the Rosetta spacecraft that point at a single isotopic reservoir, in contrast to star-forming regions. So far, it has been challenging to understand these solar system measurements in the context of the observations of protostars and disks. However, the recent detection of semi-volatile ammonium salts in comet 67P may hold the key for explaining the apparent discrepancies. Based on first results from searches of ammonium salts in star-forming regions with the Effelsberg and Greenbank telescopes, we will discuss how identifying the carrier phases of the nitrogen isotopic anomalies could lead to a more unified picture of nitrogen isotopic fractionation during the star formation process, bringing us another step closer to using the 14N/15N ratio for constraining the history of cosmomaterials.