Martian chronology

Martian chronology is currently constrained using crater counting methodologies, in situ measurements onboard the Mars Science Laboratory (MSL) Curiosity rover, and significantly more precise radiometric isotope age measurements of meteorite samples. Each methodology has advantages and drawbacks. These include uncertainties surrounding crater counting accuracy and in situ ages from MSL, and the lack of field context and two age paradoxes associated with meteorite samples. Martian crater counting is calibrated to the less-than-certain lunar crater counting chronology, and in situ ages on Mars are difficult to calibrate to provide precise or accurate dates. The martian meteorite ‘surface age’ paradox details the observation that despite significant surface area on Mars with Hesperian ages (3.7–3.0 Ga), there are no meteorites with crystallization ages from this period. The other martian meteorite paradox, the ‘ancient Pb age’ paradox, is the discrepancy in relatively young shergottite crystallization ages (4 Ga) from U–Th–Pb isotope systematics. The Mars Sample Return mission from Jezero crater holds great importance for the chronology of Mars, with its potential to elucidate the caveats within each of these chronology methods.