Subaru Telescope Detects Rare Form Of Nitrogen In Comet ISON
A team of astronomers, led by Ph.D. candidate Yoshiharu Shinnaka and Professor Hideyo Kawakita, both from Kyoto Sangyo University, successfully observed the Comet ISON during its bright outburst in the middle of November 2013. Subaru Telescope’s High Dispersion Spectrograph (HDS) detected two forms of nitrogen–14NH2 and 15NH2–in the comet. This is the first time that astronomers have reported a clear detection of the relatively rare isotope 15NH2 in a single comet and also measured the relative abundance of two different forms of nitrogen (“nitrogen isotopic ratio”) of cometary ammonia (NH3). Their results support the hypothesis that there were two distinct reservoirs of nitrogen the massive, dense cloud (“solar nebula”) from which our Solar System may have formed and evolved.
Why did the team focus on studying these different forms of nitrogen in the comet? Comets are relatively small Solar System objects composed of ice and dust, which formed 4.6 billion years ago in the solar nebula when our Solar System was in its infancy. Because they usually reside in cold regions far from the Sun, e.g., the Kuiper belt and Oort cloud, they probably preserve information about the physical and chemical conditions in the early Solar System. Different forms and abundances of the same molecule provide information about their source and evolution. Were they from a stellar nursery (a primordial interstellar cloud) or from a distinctive cloud (solar nebula) that may have formed our Solar System’s star, the Sun? Scientists do not yet understand very well how cometary molecules separate into isotopes with different abundances. Isotopes of nitrogen from ammonia (NH3) may hold the key.