Extreme seismic challenges on the Moon: requirements for targeting the faintest seismic signals from Moon interior and those of gravitational waves.
Abstract
The main goal of the Apollo 17 gravimeter was to detect oscillations of the moon excited by gravitational waves. TheApollo 17 gravimeter unfortunately failed to operate in nominal mode and provided only additional seismic records, the later obtained furthermore only after specific processing.
We start by reviewing post-Apollo amplitude of the expected signals of gravitational waves on seismic monitoring systems, either with inertial systems or strainmeters and conclude that the performances of the Apollo 17 gravimeter would have been several orders of magnitude above expected observations.. We then focus on new estimations of the micro-seismic noise of the noise including space and time noise coherency losses due to scattering. This noise is not only related to the hum of natural impacts, but also to the deep moonquake (DMQ) activity, down to the bottom part of seismic bandwidth, e.g. ~0.5 mHz. This is first done by estimating the amplitude of normal modes of the Moon for the various DMQ and then by using Apollo lunar seismicity catalog for summing up contributions of the continuous activity of DMQs. This first allow us to estimate the amplitude of the Moon Normal modes for DMQs. This includes the Slichter mode associated to a possible Moon inner core, which is a key geophysical target for estimating the density jump between inner core and outer core and therefore of the amount of light elements in the outer core. But this give us also an estimation of the micro-seismic noise, including for low order angular modes, which will be more critical as they are closer to the L=2 angular order of the gravitational wave signals. Last but not least, the challenge will even be larger for detecting gravitational waves, as these geophysical signals will in turn be a source of lunar seismic noise, which will be superimposed to the signals from gravitational waves and must therefore be corrected. We conclude with requirements for the monthly detection of normal modes, characterization of micro-seismic noise over the whole seismic bandwidth and possible seismic mode correction strategies. These seismic noise estimations are then compared to gravitational waves expected signals.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.P42C2412L