"TERRAFORMING" A MARS-LIKE PLANET BY TIDAL PROCESSES

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., 19^th 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.