On July 25, 2018, a meteoroid-associated airburst occurred near the Qaanaaq town, in Greenland, at approximately 22:00 UTC (20:00 local time). The event generated seismic waves that were recorded by two stations of the Danish Seismological Network (TULEG and NEEM) and the bolide trajectory was consequently calculated by the NASA Center for Near-Earth Object Studies (CNEOS). The total impact energy, calculated by CNEOS was 2.1 kT of TNT and the brightest point on its trajectory corresponds to an altitude of around 43 km, at a distance of about 50 km S of the Qaanaaq town and 50 km N of the TULEG station and the Thule Air Force Base [1].An airburst occurring over the icy surface of Greenland is a rare terrestrial analog for regions of the Solar System, where both an atmosphere and an icy surface exist. In the past, a variety of works had indicated the presence of ice on Titan, the biggest moon of Saturn (e.g. [2] and more recently [3]) and more precisely, the icy composition of mountains which are formed by tectonic activity [4]. Titan has a relatively thick atmosphere, compared to those of other moons in the Solar System, composed mainly (94%) of nitrogen [5]. The characterization of atmospheric meteoroid-associated seismic sources for Titan has a particular interest, as it is found that, contrary to other moons of the solar system, the presence of craters on its surface is extremely low (only about 0.4% according to [3]). The reason for this low cratering of the surface is the presence of the thick atmosphere, into which many of the meteoroids are entirely ablated into dust. Therefore, a methodology for the characterization of airbursts as seismic sources and the modeling of the associated generated seismic waves is necessary for a future seismic experiment, as any recorded signal will either be a direct atmospheric wave (nonlinear shock wave, or linear acoustic wave) or a seismic wave generated through the coupling of the atmospheric and solid/ice part. In the present study, our aim is to perform a seismic investigation of the Greenland ice shell with the use of the airburst-associated seismic source. The performed tasks into which this effort has been divided, include the application of a technique which approaches the bolide as an atmospheric seismic source, the calculation of the distance of shock wave propagation in the atmosphere, the description of the mechanism of generation of the seismic waves in the atmosphere and the solid-icy part.When the bolides enter the atmosphere of the Earth or that of any other body, shock waves are generated along the trajectory of the meteoroid. These waves are characterized by the overpressure that they generate, which create a clear pressure discontinuity in the atmosphere, referred to as the nonlinear part of the shock wave propagation. The propagation distance of this nonlinear wave is associated to the ratio of the meteoroid speed to the ambient sound speed, also known as the Mach number, as well as the physical diameter of the meteoroid. In this work, we compute this distance for the Earth case and for the known trajectory of the detected and examined bolide [1][6].The methodology developed in this study can serve the seismic investigation of structures covered by ice on planets or planetary bodies with a relatively thick atmosphere, where airbursts can occur due to the friction of the meteoroid with the ambient atmospheric material. An ideal example of this case are the icy mountains of Titan, which are known to be formed by tectonic activity on the Saturn’s moon [4]. The future Dragonfly mission to Titan will carry a seismometer as part of the DraGMet (Dragonfly Geophysics and Meteorology Package) payload [7]. Even if the primary goal of the mission is the characterization of the regolith properties, an eventual airburst and collection of seismic data near these mountainous icy structures, will be a great opportunity to investigate, through the identification of the associated waves and thus the investigation of the coupled seismic waves, the properties of this icy cover, its depth and composition.References: [1] https://cneos.jpl.nasa.gov/fireballs/ [2] Sohl, F. et al. (1995) Icarus, 115, 278–294 [3] Lopes R.M.C. et al. (2019) Nat Astron, [4] Radebaugh J. et al. (2007) Icarus, 192, 77-91, [5] Niemann H.B. et al. (2005) Nature, 438, 779–784 [6] Schmerr, N. et al. (2018) Abstract P21E-3406, AGU Fall Meeting 2018, Washington DC [7] Lorenz R. et al. (2018) Johns Hop- kins APL Technical Digest, 34, 3

Nearly all seismometers deployed on Earth are buried below the ground to achieve stable instrument temperature and greater seismic coupling. A robotically deployed science instrument PERSEUS, Pneumatic Equipment for Regolith Seismic Exploration and Underground Surveying, has been developed to address this need for lunar seismology. It is designed to bury a sonde with a seismic sensor payload into the surface of the Moon. Instrument burial reduces the scattering attenuation of seismic waves caused by the uppermost layer of and minimizes large instrument thermal fluctuations through a lunar day and night. The pneumatic burial system deploys the sonde with a threshold burial depth requirement of 0.6 meter and can drill up to 1.1 meters (with 0.9 clearance from tip-to-surface) into the lunar regolith. PERSEUS was tested in a vacuum chamber with lunar regolith analog BP-1 to successfully demonstrate the end-to-end operations.

Abstract Future missions carrying seismometer payloads to icy ocean worlds will measure global and local seismicity to determine where the ice shell is seismically active. We use two locations, a seismically active site on Gulkana Glacier, Alaska, and a more seismically quiet site on the northwestern Greenland Ice Sheet as geophysical analogs. We compare the performance of a single‐station seismometer against a small‐aperture seismic array to detect both high (>1 Hz) and low (<0.1 Hz) frequency events at each site. We created catalogs of high frequency (HF) and low frequency (LF) seismicity at each location using an automated short‐term average/long‐term average technique. We find that with a 1‐m small‐aperture seismic array, our detection rate increased (9% for Alaska and 46% for Greenland) over the single‐station approach. At Gulkana, we recorded an order of magnitude greater HF events than the Greenland site. We ascribe the HF events sources to a combination of icequakes, rockfalls, and ice‐water interactions, while very HF events are determined to result from bamboo poles that were used to secure gear. We further find that local environmental noise reduces the ability to detect LF global tectonic events. Based upon this study, we recommend that (a) future missions consider the value of the expanded capability of a small array compared to a single station, (b) design detection algorithms that can accommodate variable environmental noise, and (c) assess the potential landings sites for sources of local environmental noise that may limit detection of global events.

Line Starting Position (lat/long): 78.05494 -68.43001 Line Ending Position (lat/long): 78.06791 -68.36563

In anticipation of future spacecraft missions to icy ocean worlds, the Seismometer to Investigate Ice and Ocean Structure (SIIOS) was funded by National Aeronautics and Space Administration, to prepare for seismologic investigations of these worlds. During the summer of 2018, the SIIOS team deployed a seismic experiment on the Greenland ice sheet situated, approximately, 80 km north of Qaanaaq, Greenland. The seismometers deployed included one Trillium 120 s Posthole (TPH) broadband seismometer, 13 Silicon Audio flight-candidate seismometers, and five Sercel L28 4.5 Hz geophones. Seismometers were buried 1 m deep in the firn in a cross-shaped array centered on a collocated TPH and Silicon Audio instrument. One part of the array consisted of Silicon Audio and Sercel geophones situated 1 m from the center of the array in the ordinal directions. A second set of four Silicon Audio instruments was situated 1 km from the center of the array in the cardinal directions. A mock-lander spacecraft was placed at the array center and instrumented with four Silicon Audio seismometers. We performed an active-source experiment and a passive-listening experiment that lasted for, approximately, 12 days. The active–source experiment consisted of 9–12 sledgehammer strikes to an aluminum plate at 10 separate locations up to 100 m from the array center. The passive experiment recorded the ice-sheet ambient background noise, as well as local and regional events. Both datasets will be used to quantify differences in spacecraft instrumentation deployment strategies, and for evaluating science capabilities for single-station and small-aperture seismic arrays in future geophysical missions. Our initial results indicate that the flight-candidate seismometer performs comparably to the TPH at frequencies above 0.1 Hz and that instruments coupled to the mock-lander perform comparably to ground-based instrumentation in the frequency band of 0.1–10 Hz. For future icy ocean world missions, a deck-coupled seismometer would perform similarly to a ground-based deployment across the most frequency bands.

In this study, we report the results of an active-source seismology and ground-penetrating radar survey performed in northwestern Greenland at a site where the presence of a subglacial lake beneath the accumulation area has previously been proposed. Both seismic and radar results show a flat reflector approximately 830–845 m below the surface, with a seismic reflection coefficient of −0.43 ± 0.17, which is consistent with the acoustic impedance contrast between a layer of water and glacial ice. Additionally, in the seismic data we observe an intermittent lake bottom reflection arriving between 14–20 ms after the lake top reflection, corresponding to a lake depth of approximately 10–15 m. A strong coda following the lake top and lake bottom reflections is consistent with a package of lake bottom sediments although its thickness and material properties are uncertain. Finally, we use these results to conduct a first-order assessment of the lake origins using a one-dimensional thermal model and hydropotential modeling based on published surface and bed topography. Using these analyses, we narrow the lake origin hypotheses to either anomalously high geothermal flux or hypersalinity due to local ancient evaporite. Because the origins are still unclear, this site provides an intriguing opportunity for the first in situ sampling of a subglacial lake in Greenland, which could better constrain mechanisms of subglacial lake formation, evolution, and relative importance to glacial hydrology.

Introduction: Ocean Worlds are of high interest to the planetary community [1, 2] due to the potential habitability of their subsurface oceans [3–5]. Over the next few decades several missions will be sent to ocean worlds including the Europa Clipper [6], Dragonfly [7], and possibly a Europa lander [8]. The Dragonfly and Europa lander missions will carry seismic payloads tasked with detecting and locating seismic sources. The Seismometer to Investigate Ice and Ocean Structure (SIIOS) is a NASA PSTAR funded project that investigates ocean world seismology using terrestrial analogs. One goal of the SIIOS experiment is characterizing the local seismic environment of our field sites. Here we present an analysis of detected local events at our field sites at Gulkana Glacier in Alaska and in Northwest Greenland approximately 80 km North of Qaanaaq, Greenland (Fig. 1a). Both field sites passively recorded data for about two weeks. We deployed our experiment on Gulkana Glacier in September 2017 (Fig. 1b) and in Greenland in June 2018 (Fig. 1c). At Gulkana there was a nearby USGS weather station [9] which recorded wind data. Temperature data was collected using the MERRA satellite [10]. In Greenland we deployed our own weather station to collect temperature and wind data. Gulkana represents a noisier and more active environment: Temperatures fluctuated around 0C, allowing for surface runoff to occur during the day. The glacier had several moulins, and during deployment we heard several rockfalls from nearby mountains. In addition to the local environment, Gulkana is located close to an active plate boundary (relative to Greenland). This meant that there were more regional events recorded over two weeks, than in Greenland. Greenland’s local environment was also quieter, and less active: Temperatures remained below freezing. The Greenland ice was much thicker than Gulkana (~850 m [11] versus ~100 m [12, 13]) and our stations were above a subglacial lake. Both conditions can reduce event detections from basal motion. Lastly, we encased our Greenland array in an aluminum vault and buried it beneath the surface unlike our array in Gulkana where the instruments were at the surface and covered with plastic bins. The vault further insulated the array from thermal and atmospheric events. Event Detection and Clustering: To detect local events we filtered the data between 5-20 Hz. Using the Obspy module in python [14], we performed a short-term average/long-term average (STA/LTA) approach to determine where amplitudes spiked. For short term we used 1.5 seconds and 40 seconds and a ratio of 20 to detect events [15]. Through this approach we detect-ed 104 events at our Greenland site and 2252 events at our Gulkana site. The Gulkana site showed a strong correlation with both temperature and changes in temperature, while Greenland did not show this relationship [16]. Once we had a catalog of events, we performed a hierarchal cluster analysis to cluster events.

On July 25, 2018, a meteoroid-associated airburst occurred near the Qaanaaq town, in Greenland, at approximately 22:00 UTC (20:00 local time). The event generated seismic waves that were recorded by two stations of the Danish Seismological Network (TULEG and NEEM) and the bolide trajectory was consequently calculated by the NASA Center for Near-Earth Object Studies (CNEOS). The total impact energy, calculated by CNEOS was 2.1 kT of TNT and the brightest point on its trajectory corresponds to an altitude of around 43 km, at a distance of about 50 km S of the Qaanaaq town and 50 km N of the TULEG station and the Thule Air Force Base [1]. An airburst occurring over the icy surface of Greenland is a rare terrestrial analog for regions of the Solar System, where both an atmosphere and an icy surface exist. In the past, a variety of works had indicated the presence of ice on Titan, the biggest moon of Saturn (e.g. [2] and more recently [3]) and more precisely, the icy composition of mountains which are formed by tectonic activity [4]. Titan has a relatively thick atmosphere, compared to those of other moons in the Solar System, composed mainly (94%) of nitrogen [5]. The characterization of atmospheric meteoroid-associated seismic sources for Titan has a particular interest, as it is found that, contrary to other moons of the solar system, the presence of craters on its surface is extremely low (only about 0.4% according to [3]). The reason for this low cratering of the surface is the presence of the thick atmosphere, into which many of the meteoroids are entirely ablated into dust. Therefore, a methodology for the characterization of airbursts as seismic sources and the modeling of the associated generated seismic waves is necessary for a future seismic experiment, as any recorded signal will either be a direct atmospheric wave (nonlinear shock wave, or linear acoustic wave) or a seismic wave generated through the coupling of the atmospheric and solid/ice part. In the present study, our aim is to perform a seismic investigation of the Greenland ice shell with the use of the airburst-associated seismic source. The performed tasks into which this effort has been divided, include the application of a technique which approaches the bolide as an atmospheric seismic source, the calculation of the distance of shock wave propagation in the atmosphere, the description of the mechanism of generation of the seismic waves in the atmosphere and the solid-icy part. When the bolides enter the atmosphere of the Earth or that of any other body, shock waves are generated along the trajectory of the meteoroid. These waves are characterized by the overpressure that they generate, which create a clear pressure discontinuity in the atmosphere, referred to as the nonlinear part of the shock wave propagation. The propagation distance of this nonlinear wave is associated to the ratio of the meteoroid speed to the ambient sound speed, also known as the Mach number, as well as the physical diameter of the meteoroid. In this work, we compute this distance for the Earth case and for the known trajectory of the detected and examined bolide [1][6]. The methodology developed in this study can serve the seismic investigation of structures covered by ice on planets or planetary bodies with a relatively thick atmosphere, where airbursts can occur due to the friction of the meteoroid with the ambient atmospheric material. An ideal example of this case are the icy mountains of Titan, which are known to be formed by tectonic activity on the Saturn’s moon [4]. The future Dragonfly mission to Titan will carry a seismometer as part of the DraGMet (Dragonfly Geophysics and Meteorology Package) payload [7]. Even if the primary goal of the mission is the characterization of the regolith properties, an eventual airburst and collection of seismic data near these mountainous icy structures, will be a great opportunity to investigate, through the identification of the associated waves and thus the investigation of the coupled seismic waves, the properties of this icy cover, its depth and composition.

The Seismometer to Investigate Ice and Ocean Structure (SIIOS) is a NASA-funded analog mission program to test flight-candidate instrumentation on icy-ocean world analog sites. In September 2017, an SIIOS experiment was deployed on Gulkana Glacier. The instrumentation included a Nanometrics Trillium 120 s Posthole seismometer, four Nanometrics Trillium Compact (TC) seismometers, four Mark Products L28 geophones, and five each of Silicon Audio (SiA) 203P-15 and 203P-60 seismometers. The SiA sensors served as our flight-candidate instruments. The instrumentation was arranged in a small (<2 m) aperture array with most sensors deployed in the ice. We also placed five of the SiA seismometers on top of a mock lander to simulate placement on a lander deck. The instrumentation recorded an active-source experiment immediately after deployment and then passively for 13 days. We conducted an active-source experiment using a sledgehammer striking an aluminum plate at 13 locations, with 9–13 shots occurring at each location. During the passive observation, the experiment recorded one large Mw 7.1 event that occurred in Mexico and four other teleseismic events with Mw>6.0. The active- and passive-source signals are being used to constrain the local glacial hydrological structure, environmental seismicity, to develop algorithms to detect and locate seismic sources, and to quantify the similarities and differences in science capabilities between sensors. Initial results indicate the flight-candidate instrumentation performs comparably to the Trillium Posthole up to periods of 3 s, after which the flight-candidate performs more comparably to the TCs.

Understanding the structure and composition of the lunar interior has been designated a high priority for lunar science in two National Academies studies and the LEAG Roadmap. To that end, the Planetary Decadal Survey recommends the Lunar Geophysical Network concept as a prioritized mission under New Frontiers 5.

We have developed an optically-read inertial sensor, where microfabricated diffractive optics are used to read the displacement of a macroscale proof mass. The measured noise floor of the sensor is 3 ng/√Hz from 0.1 Hz to 100 Hz. Feedback is implemented with a macroscale motor coil and rare earth magnets, achieving a dynamic range of 176 dB. This allows the sensor to target planetary seismic applications, with field expeditions completed in Alaska and Greenland. Optical models were developed to explore the optical design space, resulting in innovate stepped grating designs which will facilitate optoelectronic integration for microscale devices.

Introduction: The Seismometer to Investigate Ice and Ocean Structure (SIIOS) project has conducted a series of seismic analog missions funded by NASA’s Planetary Science Through Analog Research (PSTAR) program. Analog studies are vital for maturing the experimental concepts that are needed prior to including a seismometer on a landed mission to an icy planetary body. To date, SIIOS experiments have been completed on a mountain glacier in the Alaska range [1] and a subglacial lake on the Greenland ice sheet. In Summer 2018, the SIIOS project conducted an Ocean Worlds analog mission in Northwest Greenland (Fig. 1) above a subglacial lake located nearly 830 m below the surface of the Greenland ice sheet [2]. The experimental objectives of this study included: 1) Quantify the difference in scientific return between what can be recovered with an array vs. a single sensor. 2) Examine the efficacy of different geometrical configurations of the seismometers within an array. 3) Quantify the difference in scientific return between a seismometer coupled directly to the ice vs. on the lander instrument ‘deck’. 4) Compare the performance of a 3-axis flight-candidate Silicon Audio seismometer with traditional seismic instrumentation. And 5) verify the depth and conditions of the lake from independent techniques to validate experimental results. Here we present the analysis that has been performed to achieve Objective #3.

The Seismometer to Investigate Ice and Ocean Structure (SIIOS) project is exploring the science capabilities of seismometers in ocean world analog environments. Ocean worlds, such as Europa, Enceladus and Titan, have thick global icy shells overlying liquid oceans. The icy shells may be seismically active due to tidal stresses. SIIOS tests several seismometers in a small-aperture array in a mock-lander configuration to quantify the ability to detect, locate, and identify seismic sources, as well as constrain local ice structure. The SIIOS experiment was deployed on two terrestrial analogs for ocean worlds. We first deployed on Gulkana Glacier in Alaska in September 2017, and then deployed in Northwestern Greenland, over a subglacial lake from May 2018-August 2018. Both areas serve as analog locations for Europa due to the layering of ice, water and rock. Gulkana was a relatively noisy site due to surface runoff and drainage, higher topographic variation (inducing rockfalls), and proximity to active plate boundaries. Greenland was a quieter site, in part due to its geologic setting high on the ice sheet, as well as from the installation process. During the Greenland deployment, we covered instruments with a large aluminum box that was buried, thus reducing noise from atmospheric and thermal effects. At both analog sites, the instruments passively recorded seismicity and seismic background noise. The passive data was used to create power spectral density (PSDs) and then probability density functions (PDFs), of the background noise. The PDFs of Gulkana showed higher noise levels compared to those of Greenland. Using the passive data, we detected and identified events originating from ice quakes, and in the case of Gulkana; rockfalls and drainage from a nearby moulin. A frequency-dependent polarization analysis was also conducted to indicate the dominant directionality of the background signals through time. The results indicate how background or ambient signals could be used on ocean worlds to characterize the local seismicity.

FOR SEISMOLOGY WITH AN OCEAN WORLD LANDER. A. G. Marusiak1, N. C. Schmerr1, S. H. Bailey2, D.N. DellaGiustina2, V.J. Bray2, P. Dahl3, E.C. Pettit4, B. Avenson5, R. C. Weber6 1University of Maryland College Park, College Park, MD (marusiak@umd.edu), 2 University of Arizona, Lunar and Planetary Laboratory, Tucson AZ, 3Applied Physics Laboratory University of Washington, Seattle WA, 4 University of Alaska Fairbanks, Fairbank AK, 5Silicon Audio, Austin TX, 6 NASA Marshall Space Flight Center, Huntsville AL

SEISMOMETER. A. G. Marusiak, N. C. Schmerr, R. C. Weber, D. N. DellaGiustina, S. H. Bailey, V. J. Bray, E. C. Pettit, C. Carr, N. Wagner, P. Dahl, B. Avenson, M. Siegler, University of Maryland, Department of Geology, College Park MD, marusiak@umd.edu NASA Marshall Space Flight Center, Huntsville, AL, University of Arizona, Lunar and Planetary Laboratory, Tucson, AZ ,University of Alaska Fairbanks, Fairbanks, AL, Applied Physics Laboratory University of Washington, Seattle Washington, Silicon Audio, Austin, TX, Planetary Science Institute, Tucson, AZ.