Mercury Has Two Permanent Thermal Bulges

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Science  19 Jan 1968:
Vol. 159, Issue 3812, pp. 306-307
DOI: 10.1126/science.159.3812.306


If Mercury has been rotating with, a period exactly two-thirds of the period of orbital revolution for at least 60,000 years, there exist two permanent thermal bulges on opposite sides of Mercury's surface that alternately face Sun at every perihelion. The bulges increase the strength of the resonance lock and tend to prevent drifting out.