Direct evidence of multiple reservoirs of volatile nitrogen in a
  protosolar nebula analogue
  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$\pm$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.
