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[56.10] Proton Irradiation of Crystalline Water Ice: Timescales for Amorphization in the Kuiper Belt

R. M. E. Mastrapa (NASA Ames Research Center), M. H. Moore (NASA Goddard Space Flight Center), R. L. Hudson (Eckerd College), R. L. Ferrante (U. S. Naval Academy), R. H. Brown (Unviersity of Arizona)

The recent discovery of crystalline water ice on Quaoar [1] has furthered the discussion concerning the phase stability of water ice in the outer solar system, and the possibilities of resurfacing by cryovulcanism [2].Jewitt and Lu estimate that the surface of Quaoar cannot be older than 10⁷ years due to 100 eV/molecule radiochemical processing of the first 0.1 microns of the surface [3].We show that, at Kuiper Belt temperatures, (<40 K), doses as low as 14 eV/molecule are capable of amorphizing crystalline water ice, significantly reducing the estimated age of the surface.

Several groups have found that ion irradiation of crystalline water ice changes the far, mid, and near infrared spectra to resemble that of amorphous ice [4-7].We confirmed the same result in the near infrared by irradiating crystalline water ice samples with 0.8 MeV protons at 9, 25, 40, 50, 70, 100, and 125 K.In our experiment, the amorphization process was strongly temperature dependent, however Leto, et al. were able to amorphize a sample at 90 K[7]. We will show the affect of irradiation on the crystalline water ice features: 1.65 microns (6061 cm^-1), 1.5 microns (6667 cm^-1), 1.56 microns (6410 cm^-1), and 2 microns (5000 cm^-1) and discuss the differences between amorphous and crystalline ice spectra [8]. NASA funding through the Planetary Atmospheres and APRA programs is acknowledged.

1. Jewitt, D.C., Nature, 2004. 432: p. 731-733.

2. Stevenson, D.J., Nature, 2004. 432: p. 681-682.

3. Cooper, J.F., Earth Moon Planets, 2003. 92(1): p. 261-277.

4. Moore, M.H., Astrophys. J., 1992. 401: p. 353-360.

5. Strazzulla, G., Europhys. Lett., 1992. 18(6): p. 517-522.

6. Baratta, G.A., Astron. Astrophys., 1991. 252(1): p. 421-424.

7. Leto, G., Memorie della Societa Astronomica Italiana Supplement, 2005. 6: p. 57.

8. Schmitt, B. in Solar System Ices. 1998. p. 199-240.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.