A very early origin of isotopically distinct nitrogen in inner Solar System protoplanets

Understanding the origin of life-essential volatiles such as nitrogen (N) in the Solar System and beyond is critical to evaluate the potential habitability of rocky planets(1-5). Whether the inner Solar System planets accreted these volatiles from their inception or had an exogenous delivery from the outer Solar System is, however, not well understood. Using previously published data of nucleosynthetic anomalies of nickel, molybdenum, tungsten and ruthenium in iron meteorites along with their N-15/N-14 ratios, here we show that the earliest formed protoplanets in the inner and outer protoplanetary disk accreted isotopically distinct N. While the Sun and Jupiter captured N from nebular gas(6), concomitantly growing protoplanets in the inner and outer disk possibly sourced their N from organics and/or dust-with each reservoir having a different N isotopic composition. A distinct N isotopic signature of the inner Solar System protoplanets coupled with their rapid accretion(7,8) suggests that non-nebular, isotopically processed N was ubiquitous in their growth zone between 0 and similar to 0.3 Myr after Solar System formation. Because the N-15/N-14 ratio of the bulk silicate Earth falls between that of the inner and outer Solar System reservoirs, we infer that N in the present-day rocky planets represents a mixture of both inner and outer Solar System material.

Automated summary

Research indicates that the earliest formed protoplanets in the inner and outer protoplanetary disk accreted isotopically distinct nitrogen, suggesting differences in nitrogen isotopic composition between the inner and outer Solar System. The nitrogen in Earth and other rocky planets represents a mixture of material from both the inner and outer Solar System.