Mars has experienced continuous asteroidal impacts throughout its history. These have produced impact-generated Mars ejecta, and a fraction of this debris is delivered to the moons of Mars: Phobos and Deimos. We studied the amount and condition of recent delivery of impact ejecta from Mars to its moons. Using state-of-the-art numerical approaches, we report that the amount of delivered materials is 10-100 times more than previously estimated, and the delivered materials are physically and chemically different from the Martian meteorites, which are all igneous rocks with a limited range of ages. We show that Mars ejecta mixed in the regolith of its moons potentially covers all its geological eras and consists of all types of rocks, from sedimentary to igneous.
Phobos and Deimos, the two small moons of Mars, are the target bodies of the Japan Aerospace eXploration Agency (JAXA) sample return mission Martian Moons eXploration (MMX). The plan for MMX is to collect samples of more than 10 g of Phobos regolith. Assuming a typical and expected grain size, at least 30 Martian grains would exist in the returned sample. These grains will provide a wealth of time-resolved geochemical information about the evolution of Martian surface environments.