A New Crater Chronology for Mars, Implications for Jezero Crater

Crater chronologies are a fundamental tool to assess relative and absolute ages of planetary surfaces when direct radiometric dating is not available. Although cratering ages are susceptible to large uncertainties (e.g., [1]), the study of the geological evolution of Mars has strongly relied on crater chronologies (e.g., [2]), for instance with the development of a global chronostratigraphy [3]. Martian crater chronologies are derived from lunar crater spatial densities on terrains with known radiometric ages, and thus they critically depend on how the extrapolation to Mars is done [2]. This requires knowledge of the time evolution of the impact flux, as well as the source of impactors. Both factors are non trivially connected to the dynamical evolution of the Solar System. Widely used martian crater chronologies (e.g., [2]) rely on simple extrapolations, and it is not clear whether and to what extent they are compatible with the dynamical evolution of the inner Solar System. Here I will present a new method to derive a martian crater chronology compatible with current understanding of the main sources of impactors in the terrestrial planet region, and Solar System dynamical models. In doing so, I will consider the main sources of uncertainties (e.g., impactor size-frequency distribution; dynamical models with “late” and “early” instabilities). The resulting “envelope” of martian crater chronologies significantly differs from previous chronologies. The new martian crater chronology is discussed using two interesting applications: Jezero crater’s dark terrain (relevant to the NASA Mars 2020 mission) and the southern highlands. Preliminary results indicate that Jezero’s dark terrain age may be older by up to ~0.8 Gyr than previously thought (e.g., [4]), while the observed number of craters larger than 150 km on the southern highlands may provide an effective constraint for early Solar System dynamical models.

1. Marchi S., et al., AJ 137, 2009

2. Hartmann W.K., Icarus 174, 2005

3. Tanaka K.L., et al., PSS 95, 2014

4. Shahrzad S., et al., GRL 10.1029/2018GL081402, 2019.