Europa's differentiated internal structure: Inferences from four Galileo encounters

Science

Volumn 281, Issue 5385, 1998, Pages 2019-2022

  Anderson, J D ^a   Schubert, G ^b   Jacobson, R A ^a   Lau, E L ^a   Moore, W B ^b   Sjogren, W L ^a  

^a CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

^b UNIVERSITY OF CALIFORNIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

EUROPA; GALILEO MISSION; PLANETARY SATELLITE;

ARTICLE; ASTRONOMY; CHEMICAL COMPOSITION; GEOMETRY; GRAVITY; MOON; PRIORITY JOURNAL; ROCK; STRUCTURE ANALYSIS;

FLIGHT EXPERIMENT; GALILEO PROJECT; LONG DURATION; UNMANNED;

EXTRATERRESTRIAL ENVIRONMENT; FERROUS COMPOUNDS; ICE; IRON; JUPITER; SILICATES; WATER;

EID: 0032566557     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.281.5385.2019     Document Type: Article

References (32)

1. The first encounter (E4) occurred on 19 December 1996, the second (E6) on 20 February 1997, the third (E11) on 6 November 1997, and the fourth (E12) on 16 December 1997; the numerical suffixes refer to orbital revolutions of Jupiter by the spacecraft.
2. J. D. Anderson, E. L. Lau, W. L. Sjogren, G. Schubert, W. B. Moore, Science 276, 1236 (1997).
3. See, for example, T. D. Moyer, Tech. Rep. TR 32-1527 (Jet Propulsion Laboratory, Pasadena, CA, 1971); B. D. Tapley, in Recent Advances in Dynamical Astronomy, B. D. Tapley and V. Szebehely, Eds. (Reidel, Dordrecht, Netherlands, 1973), pp. 396-425; J. D. Anderson, in Experimental Gravitation, B. Bertotti, Ed. (Academic Press, New York, 1974), pp. 163-199.
4. See, for example, T. D. Moyer, Tech. Rep. TR 32-1527 (Jet Propulsion Laboratory, Pasadena, CA, 1971); B. D. Tapley, in Recent Advances in Dynamical Astronomy, B. D. Tapley and V. Szebehely, Eds. (Reidel, Dordrecht, Netherlands, 1973), pp. 396-425; J. D. Anderson, in Experimental Gravitation, B. Bertotti, Ed. (Academic Press, New York, 1974), pp. 163-199.
5. See, for example, T. D. Moyer, Tech. Rep. TR 32-1527 (Jet Propulsion Laboratory, Pasadena, CA, 1971); B. D. Tapley, in Recent Advances in Dynamical Astronomy, B. D. Tapley and V. Szebehely, Eds. (Reidel, Dordrecht, Netherlands, 1973), pp. 396-425; J. D. Anderson, in Experimental Gravitation, B. Bertotti, Ed. (Academic Press, New York, 1974), pp. 163-199.
6. nm are the corresponding coefficients determined from the data.
7. nm are the corresponding coefficients determined from the data.
8. nm are the corresponding coefficients determined from the data.
9. -2) commonly used in gravimetry.
10. W. B. Hubbard and J. D. Anderson, Icarus 33, 336 (1978); S. F. Dermott, ibid. 37, 310 (1979); V. N. Zharkov, V. V. Leontjev, A. V. Kozenko, ibid. 61, 92 (1985); S. Mueller and W. B. McKinnon, ibid. 76, 437 (1988); G. Schubert, D. Limonadi, J. D. Anderson, J. K. Campbell, G. Giampieri, ibid. 111, 433 (1994).
11. W. B. Hubbard and J. D. Anderson, Icarus 33, 336 (1978); S. F. Dermott, ibid. 37, 310 (1979); V. N. Zharkov, V. V. Leontjev, A. V. Kozenko, ibid. 61, 92 (1985); S. Mueller and W. B. McKinnon, ibid. 76, 437 (1988); G. Schubert, D. Limonadi, J. D. Anderson, J. K. Campbell, G. Giampieri, ibid. 111, 433 (1994).
12. W. B. Hubbard and J. D. Anderson, Icarus 33, 336 (1978); S. F. Dermott, ibid. 37, 310 (1979); V. N. Zharkov, V. V. Leontjev, A. V. Kozenko, ibid. 61, 92 (1985); S. Mueller and W. B. McKinnon, ibid. 76, 437 (1988); G. Schubert, D. Limonadi, J. D. Anderson, J. K. Campbell, G. Giampieri, ibid. 111, 433 (1994).
13. W. B. Hubbard and J. D. Anderson, Icarus 33, 336 (1978); S. F. Dermott, ibid. 37, 310 (1979); V. N. Zharkov, V. V. Leontjev, A. V. Kozenko, ibid. 61, 92 (1985); S. Mueller and W. B. McKinnon, ibid. 76, 437 (1988); G. Schubert, D. Limonadi, J. D. Anderson, J. K. Campbell, G. Giampieri, ibid. 111, 433 (1994).
14. W. B. Hubbard and J. D. Anderson, Icarus 33, 336 (1978); S. F. Dermott, ibid. 37, 310 (1979); V. N. Zharkov, V. V. Leontjev, A. V. Kozenko, ibid. 61, 92 (1985); S. Mueller and W. B. McKinnon, ibid. 76, 437 (1988); G. Schubert, D. Limonadi, J. D. Anderson, J. K. Campbell, G. Giampieri, ibid. 111, 433 (1994).
15. -1 for coherent Doppler at a sample interval of 60 s. For data sampled at 10 s near the closest approaches to Europa, the error was increased by √6. A weighting algorithm was applied that increased the assumed standard error on the data as the spacecraft elevation angle approached the DSN station's horizon.
16. An experiment to measure tidal variations on Titan during the Cassini orbital tour of the saturnian system in 2004 to 2008 has been proposed [N. Rappaport, B. Bertotti, C. Giampieri, J. D. Anderson, Icarus 126, 313 (1997)]. A similar experiment for Europa is feasible, but because of the smaller eccentricity of Europa's orbit (∼0.009, versus an eccentricity of 0.029 for Titan), a future Europa orbiter mission would be required.
17. -3, about one-sixth the value of our upper limit.
18. -6 and μ is reduced from 0.993 to 0.988.
19. r are dominated by the 8-km error in Europa's radius.
20. 2 as a constraint on the interior models. We ignore the small differences between the three principal moments (∼0.1%).
21. C. Schubert, T. Spohn, R. T. Reynolds, in Satellites, J. A. Burns and M. S. Matthews, Eds. (Univ. of Arizona Press, Tucson, 1986), pp. 629-688; M. H. Carr et al., Nature 391, 363 (1998); R. T. Pappalardo et al., ibid., p. 365; P. E. Geissler et al., ibid., p. 368; R. Sullivan et al., ibid., p. 371.
22. C. Schubert, T. Spohn, R. T. Reynolds, in Satellites, J. A. Burns and M. S. Matthews, Eds. (Univ. of Arizona Press, Tucson, 1986), pp. 629-688; M. H. Carr et al., Nature 391, 363 (1998); R. T. Pappalardo et al., ibid., p. 365; P. E. Geissler et al., ibid., p. 368; R. Sullivan et al., ibid., p. 371.
23. C. Schubert, T. Spohn, R. T. Reynolds, in Satellites, J. A. Burns and M. S. Matthews, Eds. (Univ. of Arizona Press, Tucson, 1986), pp. 629-688; M. H. Carr et al., Nature 391, 363 (1998); R. T. Pappalardo et al., ibid., p. 365; P. E. Geissler et al., ibid., p. 368; R. Sullivan et al., ibid., p. 371.
24. C. Schubert, T. Spohn, R. T. Reynolds, in Satellites, J. A. Burns and M. S. Matthews, Eds. (Univ. of Arizona Press, Tucson, 1986), pp. 629-688; M. H. Carr et al., Nature 391, 363 (1998); R. T. Pappalardo et al., ibid., p. 365; P. E. Geissler et al., ibid., p. 368; R. Sullivan et al., ibid., p. 371.
25. C. Schubert, T. Spohn, R. T. Reynolds, in Satellites, J. A. Burns and M. S. Matthews, Eds. (Univ. of Arizona Press, Tucson, 1986), pp. 629-688; M. H. Carr et al., Nature 391, 363 (1998); R. T. Pappalardo et al., ibid., p. 365; P. E. Geissler et al., ibid., p. 368; R. Sullivan et al., ibid., p. 371.
26. M. G. Kivelson et al., Science 276, 1239 (1997).
27. K. K. Khurana et al., Nature, in press.
28. J. D. Anderson, W. L. Sjogren, G. Schubert, Science 272, 709 (1996).
29. Because Europa and the moon are similar in size and density, the expected temperature in an undifferentiated Europan mantle - produced by radiogenic heating, subsolidus convective heat transport, and temperature-dependent mantle viscosity - can be estimated from calculations carried out for the lunar interior. Lunar calculations are reported in G. Schubert, R. E. Young, P. Cassen, Philos. Trans. R. Soc. London Ser. A 285, 523 (1977). The deep mantle temperature in these lunar models is between 1500 and 1600 K.
30. P. Ulmer and V. Trommsdorff, Science 268, 858 (1995).
31. R. Woo and J. W. Armstrong, J. Geophys. Res. 84, 7288 (1979).
32. This work was sponsored by the Galileo Project and was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. G.S. and W.B.M. acknowledge support by grants from NASA through the Galileo Project at JPL and the Planetary Geology and Geophysics program.