The 2018 Qaanaaq Fireball: A Seismic Recording of a Meteorite Impact Event into the Greenland Ice Sheet

On July 25^th, 2018 at approximately 20:00 local time (UTC 22:00), local police reported that residents of the town of Qaanaaq, Greenland experienced ground shaking accompanied by a brightening of the sky, believing the phenomenon to be caused by a nearby meteorite strike. Following the event, the NASA Center for Near-Earth Object Studies (CNEOS) database of Fireballs Detected by U.S. Government Sensors reported that an atmospheric fireball event occurred on 7/25/2018 at 21:55:26 UTC, located 50 km to the south of Qaanaaq and 50 km to the north of Thule Air Force Base, coincident with the Qaanaaq fireball. CNEOS calculated the bolide had a velocity of 24.4 km/s and a total impact energy of 2.1 kilotons of TnT, with a N-NE trajectory and was brightest at 43 km altitude. Coincidentally, in May-August 2018, the Seismometer to Investigate Ice and Ocean Structure (SIIOS) team placed a seismic array situated 70 km to the north of Qaanaaq that includes multiple broadband, high sample rate seismometers configured into an analog Europa lander array, and a local 2 km aperture 4-station broadband seismometer array. The mission of the SIIOS experiment was to obtain a seismic database in a cyrospheric environment that will be used to plan for the execution and operation of future missions to icy ocean worlds. Based upon seismic recordings collected by our SIIOS seismometers and augmented by the Danish Seismological Network broadband stations TULEG and NEEM, we have located a candidate seismic event consistent with the trajectory of the projected impact point of the fireball, with an epicenter situated in the vicinity of Humboldt glacier on the Greenland ice sheet. Both atmospheric effects of the bolide and seismic energy from the putative impact were observed on seismic instruments within 350 km of the fireball. The energy of the seismic event was predominantly centered at high frequency (30 Hz) and only resolved on instruments with >100 samples per second. This candidate seismic impact event recorded by a lander-based seismic system is the first high-fidelity seismic analog for icy world impact events and will inform impact science across objects throughout the Solar System.