A corridor of exposed ice-rich bedrock across Titan’s tropical region

Abstract

Global maps of Titan show great diversity in terrain types, but their associations with specific compositions on a large scale are obscured by Titan’s thick atmosphere, which shrouds the weak spectral features. Here we develop a principal component analysis (PCA) that enables the identification of subtle spectral features. The PCA was applied to over 13,000 Cassini/VIMS spectra that cover half of Titan’s globe, focused on tropical latitudes. Our analysis detected an ice-rich linear feature of bedrock, which extends a length equivalent to 40 per cent of Titan’s circumference. This corridor is puzzling because it does not correlate with topography or measurements of the subsurface. Ice-rich terrains in other areas of Titan occur only in local regions excavated by craters or exposed by erosion, suggesting that cryovolcanism, if active, is currently not widespread. We also find evidence for a diversity of organic sediments, formed by the photolysis of Titan’s past atmospheres, which remain to be investigated, perhaps using a similar approach.

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Fig. 1: Two 0.9−3.0 μm VIMS spectra.
Fig. 2: Composition map of Titan.
Fig. 3: VIMS measurements of the second PCA component and an RT analysis of the Hotei Regio region.
Fig. 4: Titan’s largest multi-ringed crater, Menrva, centred at 20° N latitude and 87° W longitude.
Fig. 5: PCA analyses of the Selk and Sinlap craters.
Fig. 6: Radar maps compared to this study.

Data availability

The Cassini data analyszed in this work are available through the Planetary Data System (https://pds.nasa.gov). The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

Change history

  • 23 May 2019

    In the version of this Article originally published, the author Rosaly Lopes was mistakenly affiliated with Northern Arizona University. Her affiliation has now been corrected to: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.

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Acknowledgements

C.A.G.’s research is partially funded by NASA’s Cassini Program. J.T. and N.J.M.’s work were funded by NASA space grants. P. Penteado was supported by the Northern Arizona University Office of the Vice President for Research. We thank L. Soderblom for discussions on Titan’s geology, and L. Palafox for his discussions on the blind source separation.

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Contributions

C.A.G. developed, tested and interpreted the PCA analysis and led all aspects of the project. P.F.P. accessed and reduced all the Cassini data. J.T. and N.M. combed the Cassini data bank for viable and scientifically interesting cubes. G.M. contributed to the discussion of the ice-rich feature. C.D.N. contributed to the discussion of craters and other aspects of Titan’s geology. A.S. and R.M.C.L. put together the map of the distribution of major geomorphologic units on Titan (Fig. 6, bottom panel).

Corresponding author

Correspondence to Caitlin A. Griffith.

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The authors declare no competing interests.

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Journal peer review information: Nature Astronomy thanks Sylvain Douté and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Supplementary Figures 1–4, Supplementary Table 1

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Griffith, C.A., Penteado, P.F., Turner, J.D. et al. A corridor of exposed ice-rich bedrock across Titan’s tropical region. Nat Astron 3, 642–648 (2019). https://doi.org/10.1038/s41550-019-0756-5

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