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One sentence summary: The first direct detection of dinitrogen in a cometary coma by Rosetta/ROSINA indicates a low formation temperature of comet 67P/Churyumov-Gerasimenko.3 Abstract: Molecular nitrogen (N 2 ) is thought to have been the most abundant form of nitrogen in the protosolar nebula. N 2 is also the main N-bearing molecule in the atmospheres of Pluto and Triton, and was probably the main nitrogen reservoir from which the giant planets formed. Yet in comets, often considered as the most primitive bodies in the solar system, N 2 has not been detected. Here we report the direct in situ measurement of N 2 in the Jupiter family comet 67P/Churyumov-Gerasimenko made by the ROSINA mass spectrometer aboard the Rosetta spacecraft. A N 2 /CO ratio of 5.70 ± 0.66"3 was measured, corresponding to depletion by a factor of ~25.4 ± 8.9 compared to the protosolar value. This depletion suggests that cometary grains formed at low temperature conditions below ~30 K, and that the amount of N 2 delivered by comets to the terrestrial planets was a small fraction of that contributed by the other N-bearing species.Main text: Thermochemical models of the protosolar nebula (PSN) suggest that molecular nitrogen N 2 was the principal nitrogen species during the disk's phase (1) and that the nitrogen present in the giant planets was accreted in this form (2).

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The Geos 1 ion composition experiment has surveyed the plasma composition in the energy per charge range below 16 keV/e at all local times and at L=3–8. During quiet and moderately disturbed times, H+ is the dominant species with a few percent of heavy (M/Q >1) ions. Substorms and storms increase the relative amount of heavy ions, and occasionally, they can become the dominant species in the outer magnetosphere. Two sources, the solar wind (characterized by 4He++) and the ionosphere (characterized by O+), give on the average comparable contributions to storm time plasma, although in individual storms one or the other may dominate. Data presented here suggest that high‐altitude thermal plasma or the plasmasphere (characterized by He+ and O++) must be considered as a third source. Under storm conditions with Geos in the dawn‐noon local time sector we have observed a mixed composition region just inside the magnetopause where high fluxes of H+, He++, O+, and occasionally He+ ions are present. During several storms a composition profile could be measured down to L ∼3. Both O+ and He+ increase toward low altitudes, and O+ (within our energy range) can become dominant at the inner edge of the ring current. On April 30, 1978, during a storm, O+ contributed ≳8% to the total local energy density of the ring current particles at L=4.1. In no storm has He+ been observed to be the main constituent during the recovery phase. During storm recovery, H+ and O+ are the dominant ions, the H+/O+ ratio remaining constant or even increasing during the days following the main phase of the storms. This suggests that charge exchange is not the only loss mechanism for the storm time ring current and/or that H+ is replenished during the recovery phase.

Positive ion composition and electron and total positive ion densities were measured on July 30 (S26/1) and August 13 (S26/2), above Kiruna as part of a multinational rocket campaign to study noctilucent clouds (NLC). Two magnetic ion mass spectrometers took measurements at altitudes of 65-126 km in twilight at times of very low magnetic activity and of NLC sightings at 82.5-83.4 km. The hydration order of the most abundant proton hydrates increased with height from n -3 below 76 km to n = 6 and n = 5 at 88 and 87 km, respectively. Temperatures inferred from ion composition revealed a minimum of 104 ø + 20øK at 90.5 km. At this altitude a special ion spectrum with heavy proton hydrates up to H+(H20)12 was measured, which seems to indicate the possibility for ice particle formation through ion nucleation in a narrow layer. The composition measurements were also used to infer mesospheric concentrations of nitric oxide, water vapor, and hydrogen peroxide. The water vapor mixing ratio in the NLC region was found to be around 3 parts per million by volume.