Standing on the Shoulders of Apollo: Past and Future Lunar Seismology

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Standing on the Shoulders of Apollo: Past and Future Lunar Seismology Ceri Nunn Supervisor: Mark Panning Jet Propulsion Laboratory - California Institute of Technology

Past: • Introduction to Lunar Seismology • Apollo Seismic Data

Future: • Microseismometers and the Moon • Lunar Geophysical Network, Commercial Lunar Payload Services, Artemis • Key Questions • Learning from Apollo

Forward to the Moon! Past: Introduction to Lunar Seismology Lunar Seismograms from Apollo

Meteoroid impact detected by Apollo 12’s seismometer. Over 13,000 observations detected in 6+ years of operation. From: Khan et al., J. Geophys. Res. Planets, 2014 Past: Apollo Seismic Data Aims? Take the seismic data from the Apollo missions - and put it into a modern format which can be easily used and shared. Aims? Take the seismic data from the Apollo missions - and put it into a modern format which can be easily used and shared.

• SEED (Standard for the Exchange of Earthquake Data)

• ObsPy to read in and manipulate the data Locations Data

MHZ, MH1, MH2 - data traces AFR - frame count (the data were recorded in 90-block frames). ATT - timestamp recorded at the ground station (seconds since 1970-01-01). DU - digital units Saturn IV Stage Photo credit: NASA

Top 5 The Top 5 oddest things about the data The sampling rate depends on the 5 diurnal cycle (day/night) Distribution of noise and events depends 4 strongly on diurnal cycle Distribution of noise and events depends 4 strongly on diurnal cycle 3 'Zero' depends strongly on the diurnal cycle Seismometer response is out of phase in 2 the passband

Amplitude response of the seismometers Seismometer response is out of phase in 2 the passband Removing the response can have 1 unexpected results Removing the response can have 1 unexpected results Removing the response can have 1 unexpected results Apollo SEED • We provide 5 channels of data in SEED format MHZ, MH1, MH2, AFR (Frame Trace), ATT (Timing Trace)

Ultimate aim - to understand more about the structure of the Moon Future: Microseismometers and the Moon MEMS Seismometers

Micro-Electro-Mechanical Systems (MEMS) sensors are small, lightweight sensors etched on a silicon wafer.

25 mm Specification

Power 360 mW Mass 0.635 kg (3 sensors, electronics board and associated connectors and cabling) Tilt Tolerance 15° from the vertical (design to tilt tolerance of the lander) Shock Tolerance > 1000g Vibration Tolerance > 30 grms Temperature Tolerance +60°C to -196°C Downlink >259,200 kb per Earth day (compressed data) - Full Record 24 bits per sample per channel 9-10 bits per sample (after compression) +some other information from the seismometer / other instruments Downlink 5184 kb per Earth day (compressed data) - Continuous Monitoring 2 sps * 86400 s * 10 bits * 3 channels Performance Performance Impact on the Noise Floor

Lower Gravity (reduce resonant frequency)

Airless Body (thermal noise on spring)

Airless Body (Displacement transducer gain) Lower Radiation (lower noise pre-amp)

Deck Deployment

Digitisation (finer than Apollo) Performance Performance Impact on the Noise Floor

Lower Gravity (reduce resonant frequency)

Airless Body (thermal noise on spring)

Airless Body (Displacement transducer gain) Lower Radiation (lower noise pre-amp)

Deck Deployment

Digitisation (finer than Apollo) How many events? Locating Events (today)

[Christian Fröschlin] Locating Events (today)

1200 m 12 m

[NASA/GSFC/ Arizona State University] Future: Lunar Geophysical Network, Commercial Lunar Payload Services, Artemis Lunar Geophysical Network

• 4 landers, 10+ years operation • Global coverage (incl. farside, one of the poles?) • Broadband seismometer, heat ﬂow probe, surface magnetometer/EM sounding and laser retroﬂector • Additional nodes by International Partners

Mission Concept Study funded October 2019. Commercial Lunar Payload Services (CLPS)

Artist’s Impression [Astrobotic] Commercial Lunar Payload Services (CLPS)

Artist’s Impression, MX-1E Lander [MoonExpress] Commercial Lunar Payload Services (CLPS)

9 scientific payloads selected by NASA in February 2019: • Information about Entry, Descent and Landing (to support future human spaceflight) • Magnetometer • The Ion-Trap Mass Spectrometer for Lunar Surface Volatiles instrument • The Linear Energy Transfer Spectrometer • Low-frequency Radio Observations from the Near Side Lunar Surface • Stereo Cameras for Lunar Plume-Surface Studies • Surface and Exosphere Alterations • Navigation Doppler Lidar for Precise Velocity and Range Sensing • Resource Prospecting Instruments MEMS seismometers are feasible for lunar surface deployment. Future: Key Questions Key Questions

• What is the thickness of the core? Is it liquid? • How thick is the crust? • How deep are the deep moonquakes? How do they break? Are they forced by the tide? • How deep is the scattering layer? • How many meteoroids hit the Moon every year?

Structure and differentiation of the Moon -> formation and evolution Future: Learning from Apollo Learning from Apollo

• Dealing with temperature variations • Clock synchronization • Radiation • Dust • Power • Installation - leveling, orientation etc Learning from Apollo

Expect: • A lot of scatter • Thermal noise from the lander • Difﬁculty locating events

Don’t Expect: • Surface waves • Distinct phases such as PP, SS, PKP (may be possible with large events and/or stacking)

Lunar Seismology is not Terrestrial Seismology! This project was supported by strategic funds from the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

Photo Credits Artist’s Impression, Lunar Lander, Astrobotic

Alan Bean deploys the ALSEP at Apollo 12, NASA MEMS Seismometer, © Imperial College London Moon, Eric Kilby, 2015 Lunar Eclipse, Christian Fröschlin, 2019 (https:// eos.org/articles/a-meteor-struck-the-moon-during- the-total-lunar-eclipse) Backup Slides Performance

The measured spectral amplitude of the lunar seismic signals measured by Apollo compared to the performance of the InSight SP microseismometer, and the SSP target performance. From Pike, W.T., et al., 2016. in 25 - European Lunar Symposium 2016.