Crystalline water ice on the Kuiper belt object (50000) Quaoar


The Kuiper belt is a disk-like structure consisting of solid bodies orbiting the Sun beyond Neptune1. It is the source of the short-period comets and the likely repository of the Solar System's most primitive materials2. Surface temperatures in the belt are low ( 50 K), suggesting that ices trapped at formation should have been preserved over the age of the Solar System. Unfortunately, most Kuiper belt objects are too faint for meaningful compositional study, even with the largest available telescopes. Water ice has been reported in a handful of objects3,4,5, but most appear spectrally featureless5,6. Here we report near-infrared observations of the large Kuiper belt object (50000) Quaoar, which reveal the presence of crystalline water ice and ammonia hydrate. Crystallinity indicates that the ice has been heated to at least 110 K. Both ammonia hydrate and crystalline water ice should be destroyed by energetic particle irradiation on a timescale of about 107 yr. We conclude that Quaoar has been recently resurfaced, either by impact exposure of previously buried (shielded) ices or by cryovolcanic outgassing, or by a combination of these processes.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Albedo spectrum of Quaoar showing red optical continuum and distinct absorption bands at 1.5, 1.65 and 2.0 µm.
Figure 2: Near-infrared reflection spectrum of Quaoar (black) compared with a water-ice reflection spectrum10 (red).
Figure 3: Close-up of the reflection spectrum of Quaoar centred at 2.2 µm.
Figure 4: Near-infrared spectra of Pluto, Quaoar and Charon compared.


  1. 1

    Jewitt, D. & Luu, J. Discovery of the candidate Kuiper belt object 1992 QB1. Nature 362, 730–732 (1993)

    ADS  Article  Google Scholar 

  2. 2

    Davies, J. & Barrera, L. (eds) The First Decadal Review of the Edgeworth-Kuiper Belt (Kluwer Academic, Dordrecht, 2004)

  3. 3

    Brown, R. H., Cruikshank, D. P. & Pendleton, Y. Water ice on Kuiper Belt object 1996 TO66. Astrophys. J. Lett. 519, 101–104 (1999)

    ADS  Article  Google Scholar 

  4. 4

    Fornasier, S., Dotto, E., Barucci, M. A. & Barbieri, C. Water ice on the surface of the large TNO 2004 DW. Astron. Astrophys 422, L43–L46 (2004)

    ADS  Article  Google Scholar 

  5. 5

    Jewitt, D. C. & Luu, J. X. Colors and spectra of Kuiper Belt Objects. Astron. J. 122, 2099–2114 (2001)

    ADS  CAS  Article  Google Scholar 

  6. 6

    Licandro, J., Ghinassi, F. & Testi, L. Infrared spectroscopy of the largest known trans-Neptunian object 2001 KX76. Astron. Astrophys. 388, L9–L12 (2002)

    ADS  Article  Google Scholar 

  7. 7

    Brown, M. E. & Trujillo, C. A. Direct measurement of the size of the large Kuiper Belt object (50000) Quaoar. Astron. J. 127, 2413–2417 (2004)

    ADS  Article  Google Scholar 

  8. 8

    Motohara, K. et al. CISCO: Cooled infrared spectrograph and camera for OHS on the Subaru telescope. Publ. Astron. Soc. Jpn 54, 315–325 (2002)

    ADS  CAS  Article  Google Scholar 

  9. 9

    Marchi, S., Lazzarin, M., Magrin, S. & Barbieri, C. Visible spectroscopy of the two largest known trans-Neptunian objects: Ixion and Quaoar. Astron. Astrophys. 408, L17–L19 (2003)

    ADS  Article  Google Scholar 

  10. 10

    Cruikshank, D. P. et al. The composition of Centaur 5145 Pholus. Icarus 135, 389–407 (1998)

    ADS  CAS  Article  Google Scholar 

  11. 11

    Grundy, W. M. & Schmitt, B. The temperature-dependent near-infrared absorption spectrum of hexagonal H2O ice. J. Geophys. Res. 103, 25809–25822 (1998)

    ADS  CAS  Article  Google Scholar 

  12. 12

    Schmitt, B., Quirico, E., Trotta, F., Grundy, W. M. in Solar System Ices (eds Schmitt, B., de Bergh, C. & Festou, M.) 199–240 (Vol. 227, Astrophysics and Space-Science Library, Kluwer Academic, Dordrecht, 1998).

  13. 13

    Dalton, J. B., Curchin, J. M. & Clark, R. N. Temperature dependence of cryogenic ammonia-water ice mixtures and implications for icy satellite surfaces. Lunar Planet. Inst. Conf. Abstr. 32, 1496 (2001)

    ADS  Google Scholar 

  14. 14

    Owen, T. C. et al. Surface ices and the atmospheric composition of Pluto. Science 261, 745–748 (1993)

    ADS  CAS  Article  Google Scholar 

  15. 15

    Brown, M. E. & Calvin, W. M. Evidence for crystalline water and ammonia ices on Pluto's satellite Charon. Science 287, 107–109 (2000)

    ADS  CAS  Article  Google Scholar 

  16. 16

    Dumas, C., Terrile, R. J., Brown, R. H., Schneider, G. & Smith, B. A. Hubble Space Telescope NICMOS spectroscopy of Charon's leading and trailing hemispheres. Astron. J. 121, 1163–1170 (2001)

    ADS  Article  Google Scholar 

  17. 17

    Jenniskens, P., Blake, D. F., Kouchi, A. in Solar System Ices (eds Schmitt, B., de Bergh, C. & Festou, M.) 139–155 (Vol. 227, Astrophysics and Space-Science Library, Kluwer Academic, Dordrecht, 1998)

  18. 18

    Choi, Y., Cohen, M., Merk, R. & Prialnik, D. Long-term evolution of objects in the Kuiper Belt zone—Effects of insolation and radiogenic heating. Icarus 160, 300–312 (2002)

    ADS  CAS  Article  Google Scholar 

  19. 19

    Lanzerotti, L. J., Brown, W. L., Marcantonio, K. J. & Johnson, R. E. Production of ammonia-depleted surface layers on the saturnian satellites by ion sputtering. Nature 312, 139–140 (1984)

    ADS  CAS  Article  Google Scholar 

  20. 20

    Hansen, G. B. & McCord, T. B. Amorphous and crystalline ice on the Galilean satellites: A balance between thermal and radiolytic processes. J. Geophys. Res. 109, CiteID E01012 (2004)

    ADS  Article  Google Scholar 

  21. 21

    Strazzulla, G., Leto, G., Baratta, G. A. & Spinella, F. Ion irradiation experiments relevant to cometary physics. J. Geophys. Res. 96, 17547–17552 (1991)

    ADS  CAS  Article  Google Scholar 

  22. 22

    Cooper, J. F., Christian, E. R., Richardson, J. D. & Wang, C. Proton irradiation of Centaur, Kuiper Belt, and Oort Cloud objects at plasma to cosmic ray energy. Earth Moon Planets 92, 261–277 (2003)

    ADS  Article  Google Scholar 

  23. 23

    Bauer, J. M. et al. The near infrared spectrum of Miranda: Evidence of crystalline water ice. Icarus 158, 178–190 (2002)

    ADS  CAS  Article  Google Scholar 

  24. 24

    Czechowski, L. & Leliwa-Kopystyński, J. Tidal heating and convection in the medium sized icy satellites. Celest. Mech. Dyn. Astron. 87, 157–169 (2003)

    ADS  Article  Google Scholar 

  25. 25

    Kawakita, H. & Watanabe, J. Revised fluorescence efficiencies of cometary NH2: Ammonia abundance in comets. Astrophys. J. Lett. 572, 177–180 (2002)

    ADS  Article  Google Scholar 

  26. 26

    Stevenson, D. J. Volcanism and igneous processes in small icy satellites. Nature 298, 142–144 (1982)

    ADS  CAS  Article  Google Scholar 

Download references


This paper is based on observations at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We thank K. Aoki and B. Potter for help with CISCO/Subaru and C. Dumas, Y. Fernandez and T. Owen for helpful comments. This work was supported in part by a grant to D.C.J. from NASA.

Author information



Corresponding author

Correspondence to David C. Jewitt.

Ethics declarations

Competing interests

The authors declare that they have no competing financial interests.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Jewitt, D., Luu, J. Crystalline water ice on the Kuiper belt object (50000) Quaoar. Nature 432, 731–733 (2004).

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.