Comparative planetology of the history of nitrogen isotopes in the atmospheres of Titan and Mars

Isotopic constraints on the source of Pluto's nitrogen and the history of atmospheric escape

The origin and evolution of nitrogen in solar system bodies is an important question for understanding processes that took place during the formation of the planets and solar system bodies. Pluto has an atmosphere that is 99% molecular nitrogen, but it is unclear if this nitrogen is primordial or derived from ammonia in the protosolar nebula. The nitrogen isotope ratio is an important tracer of the origin of nitrogen on solar system bodies, and can be used at Pluto to determine the origin of its nitrogen. After evaluating the potential impact of escape and photochemistry on Pluto's nitrogen isotope ratio (14N/15N), we find that if Pluto's nitrogen originated as N2 the current ratio in Pluto's atmosphere would be greater than 324 while it would be less than 157 if the source of Pluto's nitrogen were NH3. The New Horizons spacecraft successfully visited the Pluto system in July 2015 providing a potential opportunity to measure 14N/15N in N2.

Constraints from Comets on the Formation and Volatile Acquisition of the Planets and Satellites

Comets play a dual role in understanding the formation and evolution of the solar system. First, the composition of comets provides information about the origin of the giant planets and their moons because comets formed early and their composition is not expected to have evolved significantly since formation. They, therefore serve as a record of conditions during the early stages of solar system formation. Once comets had formed, their orbits were perturbed allowing them to travel into the inner solar system and impact the planets. In this way they contributed to the volatile inventory of planetary atmospheres. We review here how knowledge of comet composition up to the time of the Rosetta mission has contributed to understanding the formation processes of the giant planets, their moons and small icy bodies in the solar system. We also discuss how comets contributed to the volatile inventories of the giant and terrestrial planets.