New Delhi, May 7: Two Indian geologists have interpreted surface deformations near the lunar south pole as fresh evidence for tectonic activity on the moon, corroborating earlier scientific observations that challenged the view of the moon as geologically silent.
The two geologists, from Jawaharlal Nehru University in New Delhi, have proposed that rocky debris that indicate avalanches inside two lunar craters and a 20km-long ridge-like structure called a lobate scarp near the southern polar region are surface signatures of tectonic activity.
"The lobate scarp stands out like a ridge on the moon's crust," said Saumitra Mukherjee, professor of geology at JNU.
Mukherjee, working with research scholar Priyadarshini Singh, relied on a series of images captured by India's Chandrayaan-1 spacecraft in 2008 to detect the surface deformations.
American scientists had five years ago used images from Nasa's Lunar Reconnaissance Orbiter (LRO) spacecraft to document similar lobate scarps across the lunar surface that they said suggested a contraction of the lunar interior.
Three years ago, researchers at the Space Applications Centre and the Physical Research Laboratory, both in Ahmedabad, had observed what they said were dry lava ponds, lava channels and lava vents in a lunar crater.
The new analysis has documented features called lineaments - surface manifestations of the movements of rocks underneath - and piles of crushed rocks, possibly resulting from avalanches, within two lunar craters named Cabeus B and Wiechert J.
The JNU researchers, who have described their findings in the journal Planetary and Space Science, say the avalanches too may have been triggered by the subsurface movements of the lunar crust.
"Collectively, we now have multiple lines of evidence for lunar tectonic activity," Mukherjee told The Telegraph.
US geologist Thomas Watters and his colleagues had in 2010 found lobate scarps - features that are surface expressions of thrust faults - at many sites across the lunar surface, including the scarp studied by the JNU team.
"These fault scarps are thought to be very young because of their small scale and low relief, usually only tens of metres," Watters, a senior scientist at the Smithsonian Institution's Centre for Earth and Planetary Studies, told this newspaper through email.
"Landforms of this scale will not survive for hundreds of millions of years on the moon because of the constant meteorite bombardment. These small fault scarps must be very young, less than 50 million years old, perhaps much younger," he said.
Scientists believe that a planet-sized body collided with the earth early in the history of the solar system, ejecting material that accreted into the moon. Planetary geologists had long believed that volcanism on the moon had ended within a billion years after its formation.
But discussions about lunar tectonic activity have lingered in geological circles for decades.
While seismometers placed on the moon by the Apollo missions had recorded moonquakes, most of the activity could have been attributed to meteorite strikes or the earth's gravitational pull on the moon. But, Watters said, it is possible that some moonquakes may be associated with ongoing scarp formation.
Three years ago, Watters and his colleagues had used high-resolution images from the LRO spacecraft to identify small, narrow trenches, signatures that the lunar crust is being pulled apart at these locations, Nasa's Goddard Space Flight Centre had said in a media release.
These linear valley-like structures emerge when the crust stretches, breaks and drops down along two bounding faults.