Chandrayaan-3 detects potential quakes on Moon's south pole
India's Chandrayaan-3 mission has made a groundbreaking discovery by detecting over 250 seismic signals in the Moon's south polar region. This marks the first time that seismic data has been collected from this area of the Moon, and the first such data recorded anywhere on the lunar surface since the Apollo era (1968-1972). The Instrument for Lunar Seismic Activity (ILSA) aboard the Vikram lander was responsible for this significant achievement.
ILSA: A pioneering instrument in lunar exploration
The ILSA is a pioneering instrument, being the first to record ground accelerations from the Moon's south polar region. It is also the first on the lunar surface to use sensors created using silicon micromachining technology. The experiment was conducted at a landing site of 69.37° South and 32.32° East, operating for 190 hours between August 24 and September 4, 2023.
ISRO researchers publish findings in scientific journal
The data collected by ILSA has been analyzed and published by a team of researchers from the Indian Space Research Organisation (ISRO) in the scientific journal ICARUS. The paper, authored by scientists from ISRO's Laboratory for Electro-Optics Systems (LEOS) in Bengaluru, details 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," said Sriram, director of LEOS.
Unexplained seismic signals spark curiosity
The remaining 50 signals detected by ILSA are not linked to the rover's movement or the operation of other instruments, suggesting the potential existence of Moonquakes. These unexplained signals have sparked curiosity among scientists. "There needs to be further studies to understand what may have caused these activities," Sriram added. The longest continuous signal recorded lasted for 14 minutes, with approximately 60 signals linked to Pragyan's movement controlled by ground commands.
Rover's dynamics and distance impact signal amplitude
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 increased, there was a systematic reduction in signal amplitude 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 ug (microgravity). This amplitude halved when the distance became 12m and was one order less when separation was 40m.
Uncorrelated events: A new discovery in lunar science
The data revealed nearly 50 instances where the output amplitude from the instrument was distinctly different from its normal background level. These were classified as 'uncorrelated events.' Among these, the maximum peak-to-peak amplitude reached as high as 700 ug in some instances. The frequency content in the signals is spread over a wide range up to 50Hz. These signals lasted only for a few seconds.
Theories proposed to explain uncorrelated seismic events
The unexplained signals varied significantly in nature, ranging from brief, impulsive bursts to longer, more gradual seismic events. The frequencies of these signals spanned from 1Hz to 50Hz, with some unusual high-frequency events reaching up to 94Hz. Several theories have been proposed to explain these mysterious seismic events. One possibility is that micrometeorite impacts on the lunar surface could have caused vibrations detectable by ILSA.
