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Title: Why is Mars only about one tenth of Earth's mass?
Plain: Standard models of planet formation build a Mars almost as big as Earth, yet the real Mars is about ten times lighter. Something must have removed or never supplied material near Mars's orbit.
Precise: Explain the mass of Mars (about 0.11 Earth masses) and its rapid formation (within about 10 Myr from Hf-W chronometry) in terms of the initial solid distribution or dynamical depletion: Jupiter's inward-outward migration, an early giant-planet instability, a narrow annulus of planetesimals, or pebble accretion. An answer is a scenario reproducing the masses, orbits and isotopic compositions of all terrestrial planets and the asteroid belt.
Settled by: A formation model that reproduces terrestrial planet masses and orbits and the nucleosynthetic isotope differences between Earth and Mars, and fails in its competitors.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: contested
Status note: (empty)
Posed since: (empty)