Using Young Aristarchus Basalts To Constrain Inner Solar System History
We can address one billion year uncertainties in the history of the Moon and inner solar system by landing on a young, areally extensive, homogenous lava flows of 2–3 Ga in the Aristarchus region, and obtaining 20 or more new radiometric dates. Instrumentation now exists to produce in-situ radiometric dates to well within ±200 Ma (2-σ) [1-3], including our own dating instrument, called the Chemistry, Organics, and Dating EXperiment (CODEX). The history of the lunar surface is defined by relating crater density to age through crater flux models constrained by radiometric dates of samples returned by the Apollo and Luna missions [e.g., 4, 5, 6]. However, returned samples best constrains only about 20% of the history of Moon, from ~3.5 to 4 Ga. As a result, the period from 2.5–3.5 Ga may have up to ±1 Ga of uncertainties, depending on which cratering flux model is used . The modeled relationship between crater density and the age of the Moon is extrapolated to surfaces of planetary bodies throughout the inner solar system, hence uncertainties are propagated to Mars, Venus, Mercury, and throughout the solar system [7-12]. Consequences of this uncertainty include the potential for the duration of peak lunar volcanism to extend for much longer than previously thought, requiring new geochemical models of lunar mantle evolution , and revision of our understanding of the development of one-plate planets. Furthermore, for Mars, the era of peak volcanism, volatiles, aqueous mineralogy, fluvial geomorphology, and most importantly habitability, could potentially be one billion years longer than previously recognized [14-20]. To best constrain the 2.5–3.5 Ga time period requires landing on terrain with N(1) crater densities of ~0.0015 km-2 to 0.0025 km-2, such as previously unsampled Eratosthenian near-side basalts found near Schiaparelli crater . Advantages of this area include: 1) Homogenous geochemistry consistent with Rb-Sr dating as derived from Clementine and Lunar Prospector; 2) Low regional slopes and crater abundance optimal for landing and constraining impact flux from 1-3 Ga; 3) Young model ages and undisputed crater counts; 4) Large flows covering ~4800 km2, limiting regional geologic complexity; 5) Sufficient rock abundance to produce 20-50 dates, enabling providing statistically representative constraints on surface age; 6) Sufficient LRO data to assess landing hazards and topography. We have previously published Rb-Sr results for the Duluth Gabbro, a lunar analog [1, 2]. We have recently improved our lunar analog analyses, obtaining better dates and (87Sr/86Sr)i results accurate to ~±0.0015. We assume we will be able to make at least three, likely 10, and potentially up to 20 measurements of the lava flow, enabling us to obtain dates well-within an uncertainty of ±200 Ma at 2-σ.