Letter | Published:

The rapid formation of Sputnik Planitia early in Pluto’s history

Nature volume 540, pages 9799 (01 December 2016) | Download Citation

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Abstract

Pluto’s Sputnik Planitia is a bright, roughly circular feature that resembles a polar ice cap. It is approximately 1,000 kilometres across and is centred on a latitude of 25 degrees north and a longitude of 175 degrees, almost directly opposite the side of Pluto that always faces Charon as a result of tidal locking1. One explanation for its location includes the formation of a basin in a giant impact, with subsequent upwelling of a dense interior ocean2. Once the basin was established, ice would naturally have accumulated there3. Then, provided that the basin was a positive gravity anomaly (with or without the ocean), true polar wander could have moved the feature towards the Pluto–Charon tidal axis, on the far side of Pluto from Charon2,4. Here we report modelling that shows that ice quickly accumulates on Pluto near latitudes of 30 degrees north and south, even in the absence of a basin, because, averaged over its orbital period, those are Pluto’s coldest regions. Within a million years of Charon’s formation, ice deposits on Pluto concentrate into a single cap centred near a latitude of 30 degrees, owing to the runaway albedo effect. This accumulation of ice causes a positive gravity signature that locks, as Pluto’s rotation slows, to a longitude directly opposite Charon. Once locked, Charon raises a permanent tidal bulge on Pluto, which greatly enhances the gravity signature of the ice cap. Meanwhile, the weight of the ice in Sputnik Planitia causes the crust under it to slump, creating its own basin (as has happened on Earth in Greenland5). Even if the feature is now a modest negative gravity anomaly, it remains locked in place because of the permanent tidal bulge raised by Charon. Any movement of the feature away from 30 degrees latitude is countered by the preferential recondensation of ices near the coldest extremities of the cap. Therefore, our modelling suggests that Sputnik Planitia formed shortly after Charon did and has been stable, albeit gradually losing volume, over the age of the Solar System.

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  • 31 January 2017

    The list of authors in the New Horizons Geology, Geophysics & Imagine Theme Team was included in the HTML.

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Acknowledgements

We thank NASA for its support of the New Horizons mission and the New Horizons mission team for making the July 2015 flyby possible. We thank V. Bray, B. Carcich, J. Hofgartner and F. Nimmo for helpful comments. This research was supported by a grant from NASA Origins (to D.P.H.).

Author information

Affiliations

  1. University of Maryland, College Park, Maryland, USA

    • Douglas P. Hamilton
  2. SWRI, Boulder, Colorado, USA

    • S. A. Stern
    •  & L. A. Young
  3. NASA Ames, Mountain View, California, USA

    • J. M. Moore
  4. MIT, Cambridge, Massachusetts, USA.

    • R. P. Binzel
  5. SWRI, Boulder, Colorado, USA.

    • M. W. Buie
    • , C. B. Olkin
    •  & J. R. Spencer
  6. JPL, Pasadena, California, USA.

    • B. J. Buratti
  7. Applied Physics Lab, Laurel, Maryland, USA.

    • A. F. Cheng
    •  & H. A. Weaver
  8. NASA Ames, Mountain View, California, USA.

    • K. Ennico
  9. Lowell Observatory, Flagstaff, Arizona, USA.

    • W. M. Grundy
  10. Stanford University, Stanford, California, USA.

    • I. R. Linscott
    •  & G. L. Tyler
  11. Washington University, St Louis, Missouri, USA.

    • W. B. McKinnon
  12. Ball Aerospace, Denver, Colorado, USA.

    • H. J. Reitsema
  13. NASA Goddard, Greenbelt, Maryland, USA.

    • D. C. Reuter
  14. Lunar and Planetary Institute, Houston, Texas, USA.

    • P. Schenk
  15. SETI Institute, Mountain View, California, USA.

    • M. R. Showalter

Consortia

  1. the New Horizons Geology, Geophysics & Imaging Theme Team

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  2. Search for S. A. Stern in:

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Contributions

D.P.H. wrote the manuscript and the computer codes used to produce all of the figures. S.A.S., L.A.Y. and J.M.M. commented on draft manuscripts and have leadership roles with New Horizons that helped make the mission possible.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Douglas P. Hamilton.

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https://doi.org/10.1038/nature20586

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