  Dating rocks with a precision of $\pm$200 Myr (2$\sigma$) has been required
to understand the Martian habitability and volcanic history around 4000 Myr
ago. In situ potassium-argon (K-Ar) dating techniques employing spot-by-spot
laser ablation have been developed for isochron dating on Mars. The precision
of isochron ages is predominantly determined by the relationship between the
laser spot diameter and the mineral grain size. However, the achievable age
precisions for the realistic mineralogy of Martian rocks were not investigated
yet. This study simulates isochrons under various conditions, including laser
spot size, measurement errors for K and Ar, the number of isochron points, and
the mineral compositions of representative Martian meteorites (NWA 817, Zagami,
and NWA 1068) analyzed with an electron microprobe. We find that attaining the
200 Myr precision necessitates an isochron data range wider than 6, a laser
spot diameter of 250 $\mu$m, and measurement errors of 10% for both K and Ar.
Furthermore, minimizing the variance in measurement errors between K and Ar is
essential for increasing age accuracy. This investigation demonstrates that the
required precision for Mars missions is achievable with realistic instrument
settings, thus supporting the viability of in situ K-Ar geochronology on Mars.
