In August, India made history when its unmanned Vikram lander touched down near the moon’s south pole, making it the fourth country to soft-land a spacecraft on the lunar surface. Now the many instruments on the lander and its magical Pragyan lunar rover are helping scientists understand the moon’s south polar region better than ever before.

Pragyan recently confirmed the presence of sulfur in the region. And Vikram discovered a rumble underfoot that could be evidence of a moonquake, reports LiveScience. On August 26, three days after the moon landing, the Lunar Seismic Activity Vehicle (ILSA) payload on Vikram detected an “event”, the Indian Space Research Organization said in a statement.

ILSA is designed to detect fluctuations on the lunar surface caused by natural earthquakes, impacts, and man-made events. According to ISRO, the “event” was significantly stronger than the vibrations ILSA detected from the movement of the nearby Pragyan rover.

“The source of the incident is currently being investigated.”ISRO said in a statement.

If the event is confirmed to be a moonquake, it would be the first detection on the lunar surface since the 1970s, when NASA’s Apollo missions first investigated seismic activity on the moon and detected moonquakes. The moonquake shows that the Moon is not just a big, dense space rock, but that there is actually more beneath the surface than meets the eye.

According to ISRO, the solar-powered Vikram lander and rover went into sleep mode for a 14-day night on their part of the moon. However, the devices will continue their historic mission until the “successful awakening” at the end of this month. X says ISRO.