(Reuters) - NASA's robotic probe InSight has detected and measured what scientists believe to be a "marsquake," marking the first time a likely seismological tremor has been recorded on another planet, the Jet Propulsion Laboratory in California reported on Tuesday.
The breakthrough came five months after InSight, the first spacecraft designed specifically to study the deep interior of a distant world, touched down on the surface of Mars to begin its two-year seismological mission on the red planet.
The faint rumble characterized by JPL scientists as a likely marsquake was recorded on April 6, the lander's 128th Martian day, or sol.
Scientists are still examining the data to conclusively determine the precise cause of the signal, but the trembling appeared to have originated from inside the planet, as opposed to being caused by forces above the surface, such as wind, JPL said in a news release.
"We've been collecting background noise up until now, but this first event officially kicks off a new field: Martian seismology," InSight principal investigator Bruce Banerdt said in a statement.
The tremor was so faint that a quake of the same magnitude in Southern California would be virtually lost among the dozens of tiny seismological crackles that occur there every day, JPL said.
The April 6 rumble on Mars stood out because the surface of the red planet is extremely quiet in comparison with Earth.
The size and duration of the marsquake also fit the profile of some of the thousands of moonquakes detected on the lunar surface between 1969 and 1977 by seismometers installed there by NASA's Apollo missions, said Lori Glaze, planetary science division director at NASA headquarters in Washington.
No estimated Earth-magnitude equivalent was immediately given for the apparent marsquake.
Three other apparent seismic signals were picked up by InSight on March 14, April 10 and April 11 but were even smaller and more ambiguous in origin, leaving scientists less certain they were actual marsquakes.
(Reporting by Joey Roulette in Orlando, Florida, and Steve Gorman in Los Angeles; Editing by Peter Cooney)