The Hayabusa2 re-entry provided a rare opportunity to benchmark seismic signatures due to the known trajectory and timing of its descent. By comparing the capsule's seismic profile with that of two natural meteoroids and the re-entry of a Russian Soyuz 2.1b rocket stage, researchers found clear differences. Events where the objects remained intact, including Hayabusa2 and the Soyuz stage, displayed unique, directional seismic patterns unlike those from a large North Queensland fireball that fragmented during descent.
"Understanding fragmentation helps us model how different types of space objects might behave during atmospheric entry, informing planetary defense strategies," Clemente said. Fragmentation causes shock waves to radiate energy omnidirectionally, in contrast to the focused path of intact objects, providing a way to distinguish these cases using ground-based seismic networks.
Seismic and acoustic waves generated by such events are picked up by permanent and temporary networks. In this study, two dense seismic arrays active between 2018 and 2022 across Australia enabled clear detection of the Hayabusa2 event's ballistic shock wave. "This level of station coverage is rare and enabled us to capture the ballistic shock wave signature with good clarity and a high signal-to-noise ratio," Clemente explained.
Interestingly, the signal from the Hayabusa2 capsule closely matched a 2021 fireball event over Lake Torrens. Data from the Desert Fireball Network confirmed that the fireball likely did not fragment, reinforcing the seismic findings. The network uses optical light curves to detect fragmentation events.
Seismic data can also provide insights into meteoroid composition. Weaker chondritic (stony) bodies are more prone to break up, whereas denser iron-rich meteoroids tend to stay intact. Understanding these differences contributes to statistical modeling of meteoroid types entering Earth's atmosphere.
Environmental and geologic variables such as atmospheric conditions and ground composition can affect seismic recordings. While not fully accounted for in this study, these influences are targets for future refinement. "We see tremendous potential for developing this into an operational tool for fireball characterization," said Clemente.
The research is part of a Special Focus section in SRL on the OSIRIS-REx sample capsule return from asteroid Bennu in 2023. Only four sample return events, including Hayabusa2, have ever been monitored with seismic instruments.
Research Report:Exploring Seismic Signal Detection and Source Identification of Atmospheric Entries: The Hayabusa2 Sample Return Capsule as a Benchmark
Related Links
Seismological Society of America
Asteroid and Comet Mission News, Science and Technology
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