Northeastern (46th Annual) and North-Central (45th Annual) Joint Meeting (20–22 March 2011)

Paper No. 8
Presentation Time: 3:30 PM


MALCUIT, Robert J., Geosciences Department, Denison University, Granville, OH 43023,

Planet Mars appears to be the only “normal” terrestrial planet. It still has much of its original (primitive) crust and its rotation rate, 24.6 hr/day, is what is expected for a planet of that size (MacDonald, 1963, Space Sci. Rev., 2, p. 473). In contrast, planet Earth has a large satellite that has had major effects on the rotation rate and the degassing history of the planet. The purpose of this paper is to demonstrate that A MORE COMPLEX EVOLUTIONARY PATHWAY COULD HAVE RESULTED IN THE DEVELOPMENT OF HABITABLE CONDITIONS ON A MARS-LIKE PLANET FOR SEVERAL 100 Ma.

Using the calculation procedures in Malcuit et al. (1989, Proc., 19th LPSC, p. 581), gravitational capture of a 0.2 moon-mass planetoid by a mars-like planet into a retrograde orbit is possible with a displacement Love number (h) of the planetoid near 0.2 and a specific dissipation factor (Q) near 1. A stable post-capture orbit has a semi-major axis of 126.9 mars radii and eccentricity of 0.8699. A two-body simulation program suggests that this orbit circularizes, via rock tidal energy dissipation processes, over about 600 Ma to a circular retrograde orbit of about 30 mars radii. The rock tides in the equatorial zone of the mars-like planet decrease from a maximum of about 18 km at the time of capture to about 2 meters at 30 mars radii. The circular retrograde orbit slowly decreases in semi-major axis as the prograde rotation rate of the mars-like planet decreases to zero when the satellite orbit is at about 20 mars radii. The retrograde rotation rate of the planet then gradually increases to 31 hr/day when the retrograde satellite is at 13 mars radii; 23 hr/day at 11 mars radii; and 10 hr/day at 3 mars radii. The equilibrium rock tidal amplitudes at 13, 11, and 3 mars radii are about 25, 42, and 2000 m, respectively. The satellite would eventually break up as it gets within the Roche limit for a solid body (Aggarwal and Oberbeck, 1974, Astrophys. Jour., 191, p. 577) at about 1.6 mars radii. The final rotation rate for the mars-like planet in this scenario is about 8.3 hr/day retrograde and the surface of the planet would be a basaltic inferno similar to that of planet Venus during the “global resurfacing event”. In conclusion, a mars-like planet could be “terraformed” into a habitable condition for several 100 Ma when the retrograde rotation rate of the mars-like planet is between 31 and 15 hr/day.