The origin of Phobos grooves from ejecta launched from impact craters on Mars: Tests of the hypothesis

► Grooves from martian ejecta require implausible flight formation precision. ► Ejecta flight times would vary, yet evidence of varying dispersion is not observed. ► Millions of identical ejecta blocks must be produced, and all other ejecta excluded. ► Mercury and the Moon manifest no Phobos-like grooves in character, density or scale. ► The secondary impact flux from Mars is severely insufficient to produce the grooves.