Possible detection of hydrazine on Saturn’s moon Rhea

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Science Advances  22 Jan 2021:
Vol. 7, no. 4, eaba5749
DOI: 10.1126/sciadv.aba5749
  • Fig. 1 Location of the four Cassini UVIS/FUV observations analyzed in this paper.

    UVIS observations sample Rhea’s leading and trailing hemispheres. Each slit field of view represents 64 spatial pixels of the detector. Area within each box represents the integrated sum of all 64 detector rows, over all phase angle ranges.

  • Fig. 2 UVIS-measured reflectance spectra (black spectra) of Rhea from the four observations shown in shown in Fig. 1 and Table 1.

    Spectral models are based on laboratory thin-ice measurements of the absorbance of two chloromethane compounds and N2H4.H2O. Measurements were acquired at a temperature of 70 K under near-vacuum conditions to simulate surface environment of Rhea. Grain size used in the model spectra was 3 μm, and path length was set to 0.125 μm for Obs 1, 2, and 3, and 0.250 μm for Obs 4. Error, ±6% for the observational data, not added to spectra for clarity.

  • Fig. 3 Continuum-removed spectra showing the relative depth of the 184-nm absorption feature and relative positions of water-ice absorption edge.

    Within error limits of UVIS data, we detect no significant differences in the strength of the 184-nm absorption feature as a function of location on Rhea’s surface. A minor change in the position of UV absorption edge due to water-ice is noted. The minor shift may be the result of different ice grain sizes and/or minor contaminants within the ice matrix. Error, ±6%, not added to spectra for clarity.

  • Fig. 4 Deuterium chloride spectrum compared with a Rhea FUV spectrum.

    Error, ±6% for the observational data and ±5% for the experiment data, not added to spectra for clarity.

  • Fig. 5 Cassini UVIS/FUV disk-integrated spectra of trailing hemisphere of Saturn’s icy moon Tethys acquired during 2015.

    Observations were collected at a phase angle of ~29°. All three spectra are dominated by water-ice as indicative of steep FUV drop-off between ~160 and 170 nm. None of the spectra show the presence of the 184-nm absorption feature that is seen in FUV spectra of Rhea. Error, ±6%, not added to spectra for clarity.

  • Table 1 Table of Cassini UVIS observations presented in this paper.

    In the table, Lat1 and Lat2 are the latitude boundaries of the instrument footprint, Long1 and Long2 are the longitude boundaries, Phase is the phase angle (°), Incidence and Emission are the incidence and emission angles of the UVIS observation, and Range is the distance above the target surface on Rhea (in kilometers). The first and second rows for each observation list the start and end times of observation, respectively.


Supplementary Materials

  • Supplementary Materials

    Possible detection of hydrazine on Saturn’s moon Rhea

    Mark Elowitz, Bhalamurugan Sivaraman, Amanda Hendrix, Jen-Iu Lo, Sheng-Lung Chou, Bing-Ming Cheng, B. N. Raja Sekhar, Nigel J. Mason

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    This PDF file includes:

    • Hapke Spectral Modeling
    • Fig. S1
    • Table S1
    • References

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