Evidence that Mars is a former moon

Much less massive than any planet not itself suspected of being a former moon

Orbit has eccentricity of near 10%, as would be expected for an escaped moon.

Spin is slower than larger planets, except where a massive moon has intervened (Mercury escaped from Venus; Moon robbed Earth of original 2-4 hour spin rate.)

Large offset of center of figure from center of mass – common for moons, not for planets

Shape not in equilibrium with spin, indicating reshaping by some cataclysm

South hemisphere is saturated with craters, the north has sparse cratering – indicates either a removal mechanism in the north or a massive cratering event in the south

The crustal dichotomy boundary is nearly a great circle – indicates that something nearby but external to Mars and short-lived devastated half the planet

North hemisphere has smooth, 1-km-thick crust; rough southern crust is up to 20-km thick – suggests massive bombardment of the south half from a planet-sized source

Crustal thickness in south decreases gradually toward hemisphere edges – consistent with external event, but not a local one

Lobate scarps occur near hemisphere divide, compressed perpendicular to boundary – indicates that impacts near the hemisphere boundary were extreme grazers

Huge volcanoes arose where uplift pressure from mass redistribution following pole change is maximal – consistent with present shape not being in equilibrium

Sudden 90° geographic pole shift occurred – as would happen if a great mass were added to one hemisphere centered on Mars equator, causing planet to tip over

Much of original atmosphere has been lost – as would result from a major cataclysm

A sudden, massive flood with no obvious source occurred – cataclysm may have brought the water from oceans on the source body

Xe¹²⁹, a fission product of massive explosions, has an excess abundance on Mars

Crustal magnetization in southern highlands is weak to absent in northern lowlands