PAPER 10 OF THE LEF SERIES
Mars: The Piston and the Ring
How a fast, expanded Mars launched Deimos and Phobos
Abstract
Phobos and Deimos circle Mars on near-circular, equatorial orbits, one inside and one outside the corotation radius. Deimos is smooth and rounded; Phobos is scored by long grooves. We propose that both moons were fired from one volcanic conduit, at Pavonis Mons, by a young Mars 1.5 times its present radius that turned once in five hours. At its equator a departing body carried a free sideways speed of 1.78 km/s, and the effective gravity was a quarter of today's. Pavonis then stood about 30 km high, and steam carrying rock fragments had drilled a conduit through its height. Trapped gas drove a soft, sealing plug of crust up that conduit in less than a minute. Rising through a dense steam atmosphere that turned with the planet, the plug needed an outward speed of 1.3–1.5 km/s to reach the ring just beyond the corotation line, 1.9–2.4 km/s without that help. Deimos was the first plug, small and light; Phobos the second, larger, and braked in the conduit. The sideways speed they still lacked came from a ring that Mars had built earlier from its own steam: a body crossing it is dragged toward orbital speed and gains a rounded, equatorial orbit, while the same friction grinds it. The tide of the young, soft Mars then pushed each moon outward. Deimos passed the final corotation line, 20,428 km, before the line reached it, and was ground smooth. Phobos met only the thin inner edge of a waning ring, kept its grooves, and was caught by the moving line near 19,000 km. The paper ends with predictions, each with its value, instrument and date, among them the MMX samples of Phobos due in 2031.
Keywords: Mars; Phobos; Deimos; Pavonis Mons; volcanic conduit; circumplanetary ring; corotation radius; tidal evolution; MMX
How to cite
Duran, Z. (2026). Mars: The Piston and the Ring. How a fast, expanded Mars launched Deimos and Phobos. Paper 10 of the LEF series. https://lef-model.com/paper10.html