Surveying exogenous species in Saturn with ALMA. II. Detecting and Mapping HCN
Abstract
Several external sources (the rings, the satellites, cometary impacts, interplanetary dust particles) supply material to the upper atmosphere of Saturn. The signature of this external influx has been documented on the ionospheric electronic and ionic densities, and in the stratosphere on oxygenated molecules (CO, CO2, H2O). We search for the chemical signature of the external sources in nitrogen-bearing species in Saturn's stratosphere. We have targeted the HCN(4-3) rotational line and mapped its emission line at the planet limb with ALMA in 2018 with configuration C43-3, providing a synthetic beam of 0.61"x0.50". HCN was detected at all observable latitudes from 20°S to 60°N. The HCN abundance was measured at two independent pressure levels, 0.1 and 1 hPa. The measured volume mixing ratios are latitudinally uniform within uncertainties at both pressure levels. The mean vmr is (7± 2)× 10−11 and (4± 1)× 10−12 at 0.1 and 1 hPa respectively. This corresponds to a mean column-density of (4± 1)× 1012 cm−2, and a total nitrogen mass of (3.7 ± 0.9)× 1010 g. The steep vertical profile suggests that another loss mechanism, possibly sticking or heterogeneous chemistry on aerosols, is active besides photodissociation. The huge influx of material detected in the ring plane by Cassini left no detectable chemical signature on HCN. The detected HCN mass seems compatible with several sources: the ring rain at mid-latitudes, Enceladus, or an old cometary impact. The detected HCN could also be a chemical product of internal N2 transported from the deep atmosphere up to the stratosphere.
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BibTeX
@misc{fouchet2026surveying,
title = {{Surveying exogenous species in Saturn with ALMA. II. Detecting and Mapping HCN}},
author = {T. Fouchet and T. Cavalié and R. Moreno and S. Guerlet and E. Lellouch and D. Bardet},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.34943},
eprint = {2609.34943},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.34943},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Surveying exogenous species in Saturn with ALMA. II. Detecting and Mapping HCN
AU - T. Fouchet
AU - T. Cavalié
AU - R. Moreno
AU - S. Guerlet
AU - E. Lellouch
AU - D. Bardet
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2609.34943
UR - https://arxiv.org/abs/2609.34943
AB - Several external sources (the rings, the satellites, cometary impacts, interplanetary dust particles) supply material to the upper atmosphere of Saturn. The signature of this external influx has been documented on the ionospheric electronic and ionic densities, and in the stratosphere on oxygenated molecules (CO, CO2, H2O). We search for the chemical signature of the external sources in nitrogen-bearing species in Saturn's stratosphere. We have targeted the HCN(4-3) rotational line and mapped its emission line at the planet limb with ALMA in 2018 with configuration C43-3, providing a synthetic beam of 0.61"x0.50". HCN was detected at all observable latitudes from 20°S to 60°N. The HCN abundance was measured at two independent pressure levels, 0.1 and 1 hPa. The measured volume mixing ratios are latitudinally uniform within uncertainties at both pressure levels. The mean vmr is (7± 2)× 10^−11 and (4± 1)× 10^−12 at 0.1 and 1 hPa respectively. This corresponds to a mean column-density of (4± 1)× 10^12 cm^−2, and a total nitrogen mass of (3.7 ± 0.9)× 10^10 g. The steep vertical profile suggests that another loss mechanism, possibly sticking or heterogeneous chemistry on aerosols, is active besides photodissociation. The huge influx of material detected in the ring plane by Cassini left no detectable chemical signature on HCN. The detected HCN mass seems compatible with several sources: the ring rain at mid-latitudes, Enceladus, or an old cometary impact. The detected HCN could also be a chemical product of internal N2 transported from the deep atmosphere up to the stratosphere.
ER -