  Geochronology, or determination of absolute ages for geologic events,
underpins many inquiries into the formation and evolution of planets and our
Solar System. Absolute ages of ancient and recent magmatic products provide
strong constraints on the dynamics of magma oceans and crustal formation, as
well as the longevity and evolution of interior heat engines and distinct
mantle/crustal source regions. Absolute dating also relates habitability
markers to the timescale of evolution of life on Earth. However, the number of
geochronologically-significant terrains across the inner Solar System far
exceeds our ability to conduct sample return from all of them. In preparation
for the upcoming Decadal Survey, our team formulated a set of medium-class (New
Frontiers) mission concepts to three different locations (the Moon, Mars, and
Vesta) where sites that record Solar System bombardment, magmatism, and/or
habitability are uniquely preserved and accessible. We developed a notional
payload to directly date planetary surfaces, consisting of two instruments
capable of measuring radiometric ages in situ, an imaging spectrometer, optical
cameras to provide site geologic context and sample characterization, a trace
element analyzer to augment sample contextualization, and a sample acquisition
and handling system. Landers carrying this payload to the Moon, Mars, and Vesta
would likely fit into the New Frontiers cost cap in our study (~$1B). A mission
of this type would provide crucial constraints on planetary history while also
enabling a broad suite of investigations such as basic geologic
characterization, geomorphologic analysis, ground truth for remote sensing
analyses, analyses of major, minor, trace, and volatile elements, atmospheric
and other long-lived monitoring, organic molecule analyses, and soil and
geotechnical properties.
