India's Chandrayaan-3 mission has detected over 250 seismic signals in the Moon's south polar region. Among these, 50 distinct signals remain unexplained, suggesting the possibility of Moonquakes. This marks the first time seismic data has been collected from the lunar south pole and the first since the Apollo missions.

Seismic Data from the South Pole

The Instrument for Lunar Seismic Activity (ILSA), housed aboard the Vikram lander, conducted this experiment at coordinates 69.37° South and 32.32° East, operating continuously for 190 hours between August 24 and September 4, 2023.

ILSA is not only the first instrument to record ground vibrations in the Moon's south polar region, but it is also pioneering in its use of sensors crafted through silicon micromachining technology on the lunar surface. The findings from this experiment have been meticulously analysed and published by researchers from the Indian Space Research Organisation (ISRO) in the scientific journal ICARUS. The paper, authored by a team from ISRO’s Laboratory for Electro-Optics Systems (LEOS) in Bengaluru, documents the results of the study.

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Unexplained Seismic Events

According to the research, out of the more than 250 seismic events recorded, approximately 200 can be linked to known activities, such as the movement of the Pragyan rover or the operation of other scientific instruments. However, around 50 signals remain unexplained, with no clear link to the rover's movements or any other activity. "Further studies are needed to understand what may have caused these uncorrelated events," said KV Sriram, Director of LEOS, told TOI.

The most significant signals recorded by ILSA were associated with the navigation of the Pragyan rover. The longest continuous signal recorded lasted 14 minutes, and about 60 signals have been connected to Pragyan's movement, which was controlled remotely. As the rover moved away from ILSA, researchers noted a systematic reduction in the amplitude of the recorded signals. For instance, when the rover was approximately 7 metres from the lander, the peak-to-peak amplitude was around 200 µg (microgravity), which decreased as the distance increased.

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Despite the primary focus of ILSA not being the detection of deep or shallow Moonquakes, the data revealed approximately 50 instances where the instrument recorded significant deviations from the normal background level, suggesting the presence of seismic events not linked to any known activity. These were classified as "uncorrelated events" by the researchers.

Among these uncorrelated events, the maximum peak-to-peak amplitude reached up to 700 µg in some cases. The frequency content of these signals ranged widely, extending up to 50 Hz, with most of them lasting only a few seconds. While several shorter signals were also detected, they were not included in the study's final count.

Significant Advances in Lunar Science

Chandrayaan-3's mission has provided significant advancements in lunar science, particularly in understanding seismic activity in the Moon's south polar region. The discovery of unexplained seismic events opens new avenues for research and exploration. Continued studies are crucial to uncover the origins of these signals and to further our understanding of the Moon’s geological activity.