India's Chandrayaan-3 mission has detected over 250 seismic signals in the Moon's south polar region, including at least 50 distinct ones that are not linked to the rover's movement or the operation of other instruments, suggesting the potential existence of Moonquakes. This marks the first time seismic data has been collected from the Moon’s southern polar region, and the first such data recorded anywhere on the lunar surface since the Apollo era. The Instrument for Lunar Seismic Activity (ILSA) aboard the Vikram lander conducted this experiment at the landing site of 69.37° South and 32.32° East, operating for 190 hours between August 24 and September 4, 2023.
ILSA is the first instrument to record ground accelerations from the Moon's south polar region and the first on the lunar surface to employ sensors created using silicon micromachining technology. The findings from this data have been analyzed and published by a group of researchers from ISRO in the scientific journal ICARUS. The paper written by J John, V Thamarai, Teena Choudhary, MN Srinivasa, Ashwini Jambhalikar, MS Giridhar, Madan Mohan Mehra, Mayank Garg, KV Shila, Krishna Kummari, SP Karantha, Kalpana Arvind, and KV Sriram, all hailing from ISRO’s Laboratory for Electro-Optics Systems (LEOS) in Peenya, Bengaluru, captures these findings.
“Of the more than 250 seismic events recorded, approximately 200 signals correlate to known activities involving Pragyan’s movements or the operation of scientific instruments, the 50 others do not have any explanation. There needs to be further studies to understand what may have caused these activities,” said Sriram, the director of LEOS, in an interview with TOI.
The most extended and relatively significant amplitude records from ILSA correspond to the navigation of the Pragyan rover. The longest continuous signal recorded lasted for 14 minutes. Approximately 60 signals cataloged are linked to Pragyan's movement controlled by ground commands. The rover, which weighed about 25kg, was driven with motors and moved at a typical speed of 1 cm per second. The dynamics of the rover and the wheel-soil interaction introduced complex ground vibration signals to ILSA.
“As the distance of the rover from ILSA was increased, there had been a systematic reduction in the amplitude of the signal under normal roving conditions. For example, when the rover was away from the lander by around 7m, the average peak to peak amplitude was around 200 µg (microgravity). This amplitude was halved when the distance became 12m and was one order less when the separation was 40m,” the paper reads.
Researchers noted that events categorized as deep or shallow quakes were beyond the targeted objectives and design specifications of ILSA, and they were aware of the low probability of such occurrences during the one lunar day operation. Still, the data revealed approximately 50 instances where the output amplitude from the instrument was distinctly different from its normal background level.
“From the mission command history, it was confirmed that any activity that can cause ground vibration was not performed during this timeframe,” the paper reads. Researchers classified these as ‘uncorrelated events.’
Among the 50 uncorrelated events, the maximum peak-to-peak amplitude reached as high as 700 µg in some instances. “The frequency content in the signals is spread over a wide range up to 50 Hz. The signals discussed here lasted only for a few seconds. Although several distinct signals lasting less than a couple of seconds are also observed, they are not included in the count reported in this paper,” the researchers noted.
These findings from Chandrayaan-3's mission represent significant advancements in lunar science, offering new insights into the Moon's seismic activity, particularly in its southern polar region. Further studies are essential to understand the origins of the unexplained seismic events detected.
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