5. M.J. Mumma, R.E. Novak, M.A. DiSanti, and B.P. Bonev, “A Sensitive Search for Methane on Mars,” AAS/DPS 35th Meeting, September 1–6, 2003.

6. V.A. Krasnopolsky, J.P. Maillard, and T.C. Owen, “Detection of Methane in the Martian Atmosphere: Evidence for Life,” European Geophysical Union Meeting, Nice, May 2004.

7. V. Formisano, S. Atreya, T. Encrenaz, N. Ignatiev, and M. Giuranna, “Detection of Methane in the Atmosphere of Mars,” Science 306: 1758–1761, 2004.

8. J.S. Kargel, “Proof for Water, Hints of Life?” Science 306: 1689–1691, 2004.

9. See, for example, T. Owen, “Huygens Rediscovers Titan” and references therein, Nature 438: 756–757, 2005.

10. D.A. Fischer and J.A. Valenti, “Metallicities of Stars with Extrasolar Planets,” Scientific Frontiers in Research on Extrasolar Planets, D. Deming and S. Seager, eds., ASP Conference Series 294, pp. 117–128, 2003; available online at <http://exoplanets.org/iau_proc.pdf>.

11. S. Ida and D.N.C. Lin, “Toward a Deterministic Model of Planet Formation II: The Formation and Retention of Gas Giant Planets Around Stars with a Range of Metallicities,” Astrophysical Journal 616: 567–572, 2004.

12. The solar oxygen and carbon abundances were revised downward by a factor of 1.38 and 1.35, respectively, in: C.A. Prieto, D.L. Lambert, and M. Asplund, Astrophysical Journal Letters 556: 63–66, 2001; and C.A. Prieto and D.L. Lambert, Astrophysical Journal Letters 573: 137–140, 2002. For more details, see for example, W.B. Hubbard, “The Core Problem,” Nature 431: 32, 2004.

13. National Aeronautics and Space Administration, The Vision for Space Exploration: February 2004, National Aeronautics and Space Administration, Washington, D.C., 2004.

14. President’s Commission on Implementation of United States Space Exploration Policy, A Journey to Inspire, Innovate, and Discover, U.S. Government Printing Office, Washington, D.C., 2004.

15. National Research Council, New Frontiers in the Solar System: An Integrated Exploration Strategy, The National Academies Press, Washington, D.C., 2003, pp. 203 and 205.

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