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Science 21 January 1972:
Vol. 175. no. 4019, pp. 317 - 320
DOI: 10.1126/science.175.4019.317
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Articles

Mariner 9 Celestial Mechanics Experiment: Gravity Field and Pole Direction of Mars

J. Lorell 1, G. H. Born 1, E. J. Christensen 1, J. F. Jordan 1, P. A. Laing 1, W. L. Martin 1, W. L. Sjogren 1, I. I. Shapiro 2, R. D. Reasenberg 2, and G. L. Slater 2

1 Jet Propulsion Laboratory, California Institute of Technology, Pasadena 91103
2 Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, Cambridge 02139

Analysis of the Mariner 9 radio-tracking data shows that the Martian gravity field is rougher than that of Earth or the moon, and that the accepted direction of Mars's rotation axis is in error by about 0.5°. The new value for the pole direction for the epoch 1971.9, referred to the mean equatorial system of 1950.0, is right ascension agr= 317.3° ± 0.3°, declination dgr = 52.6° ± 0.2°. The values found for the coefficients of the low-order harmonics of Mars's gravity field are as follows: J2=(1.96±0.01)x10-3, referred to an equatorial radius of 3394 kilometers; C22 = -(5 ± 1) x 10-5; and S22 = (3 ± 1) x 10-5. The value for J2 is in excellent agreement with the result from, Wilkins' analysis of the observations of Phobos. The other two coefficients imply a value of (2.5 ± 0.5) x 10-4 for the fractional difference in the principal equatorial moments of inertia; the axis of the minimum moment passes near 105°W.


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Large-Scale Variations in the Obliquity of Mars.
W. R. Ward (1973)
Science 181, 260-262
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Is the Moon Hot or Cold?.
D. L. Anderson, D. L. Anderson, and T. C. Hanks (1972)
Science 178, 1245-1249
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Mariner 9 Science Experiments: Preliminary Results.
R. H. Steinbacher, R. H. Steinbacher, A. Kliore, J. Lorell, H. Hipsher, C. A. Barth, H. Masursky, G. Munch, J. Pearl, and B. Smith (1972)
Science 175, 293-294
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