CRATER CLOCK: Calibration of the Cratering Chronometer for the Earliest Planetary Evolution

The Crater Clock project is dedicated to the calibration of the cratering chronometer for the earliest planetary evolution. The understanding of the evolution of planets in the Solar System critically depends on accurate estimates of time and rates at which processes, e.g. volcanism, occur. Absolute time scales for planetary surfaces evolution in the inner Solar system (except the Earth and the Moon) can only be derived by linking the lunar cratering frequencies with isotopically dated lunar samples. The Crater Clock team develops a unique cratering chronology model considering different bombardment histories and their implications: We use numerical models for impact crater formation and small body orbital evolution to evaluate the crater-projectile size relationship and the projectile impact probability. Using statistical methods we compare these model results with observations on the lunar and martian surface. The goal is to bridge the divide between the theoretical estimates for the dynamically evolving Solar System and new and modern isotope (age) results. This novel and unique planetary time-scale will for the first time permit studies of the earliest and most constitutive period of planetary evolution (the first 600 Ma) by which the pattern of mantle dynamics, the thermal evolution is defined, and to date important phases of crustal formation and volcanic activity. The model and results derived from this project will offer guidance for sample site selections of future multi-sample return missions.

Accurate time and rates at which processes occur, e.g. volcanism, are critical for the interpretation of planetary evolution. Absolute time scales for planetary surfaces evolution (except the Earth and the Moon) can only be derived by linking the lunar cr atering frequencies with isotopically dated lunar samples. This approach, however, is controversial. Commonly, cratering statistics for planetary surface-age determination assumes monotonic cratering rate decay, but this assumption may be flawed. Indicati ons are the erroneous ages derived from cratering-statistics: For example, (1) the oldest remaining planetary surfaces appear younger than expected from isotope ages of returned Moon samples or meteorites, (2) basin-forming events do not occur simultaneou sly on all terrestrial planets during the Late Heavy Bombardment period (around 3.9 Ga), and (3) no time scale exist to asses the period prior to the Late Heavy Bombardment. This implies that any dates for possible primal life on Mars, or the timing and r ates of volcanism, an expression of planetary thermal evolution, are, so far, unreliable for the first 600 Myr. With the availability of new high resolution space mission data, it is timely to calibrate the cratering-based age-determination technique for this earliest phase of planetary evolution. The Crater Clock team will develop a unique cratering chronology model (i.e., for time-variable crater diameters) that will bridge the divide between the theoretical estimates for the dynamically evolving Solar System and new and modern isotope (age) results. With this novel and unique planetary time-scale, which will for the first time permit studies of the earliest and most constitutive period of planetary evolution (the first 600 Myr), we will assess the the rmal evolution of the terrestrial planetary bodies.