Lunette: A Dual Lander Mission to the Moon to Explore Early Planetary Differentiation

Abstract

The Moon is critical for understanding fundamental aspects of how terrestrial planets formed and evolved. The Moon’s size means that a record of early planetary differentiation has been preserved. However, data from previous, current and planned missions are (will) not (be) of sufficient fidelity to provide definitive conclusions about its internal state, structure, and composition. Lunette rectifies this situation. Lunette is a solar-powered, 2 identical lander geophysical network mission that operates for at least 4 years on the surface of the Moon. Each Lunette lander carries an identical, powerful geophysical payload consisting of four instruments: 1) An extremely sensitive instrument combining a 3-axis triad of Short Period sensors and a 3-axis set of Long Period sensors, to be placed with its environmental shield on the surface; 2) A pair of self-penetrating “Moles,” each carrying thermal and physical sensors at least 3 m below the surface to measure the heat flow from the lunar interior; 3) Lunar Laser Ranging Retro-Reflector: A high-precision, high-performance corner cube reflector for laser ranging between the Earth and the Moon; and 4) ElectroMagnetic Sounder: A set of directional magnetometers and electrometers that together probe the electrical resistivity and thermal conductivity of the interior. The 2 landers are deployed to distinct lunar terranes: the Feldspathic Highlands Terrane (FHT) and the Procellarum KREEP Terrane (PKT) on the lunar nearside. They are launched together on a single vehicle, then separate shortly after trans-lunar injection, making their way individually to an LL2 staging point. Each lander descends to the lunar surface at the beginning of consecutive lunar days; the operations team can concentrate on completing lander checkout and instrument deployments well before lunar night descends. Lunette has one primary goal: Understand the early stages of terrestrial planet differentiation. Lunette uses Apollo knowledge of deep moonquake nests and Earth-based nearside impact flash monitoring (IFM) to enable a 2-station mission to address this goal. IFM provides known seismic sources, allowing detailed seismic study of the lunar interior from a 2-station network, representing a major advance since Apollo. The instruments and support systems are designed to operate for much longer than four years and therefore could be integrated into any future international lunar geophysical network. Modeling undertaken demonstrates the feasibility of this approach for seismic data. Using the Apollo seismic record, the sensitivity and broadband nature of the seismometer is shown to be able to address the challenges of seismic scattering, low frequency seismology, detection of core phases (e.g. PKP, ScS), and meteoroid impact characterization to achieve the primary mission goal.