Recently detected small lava flows on the surface of the moon suggest lunar volcanic activity slowed gradually nearly a billion years later than previously thought. 

A new study published Sunday in the journal, Nature Geoscience, further argues that radioactive elements could be keeping the innards of the moon warmer. Current theory holds the moon's interior went cold a long time ago.

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The moon likely formed about 4.5 billion years earlier and is the debris of a collision between Earth and another small planet about the size of Mars. Its fiery origin kept its surface molten.

The vast basaltic plains known as maria then formed on the lunar surface about 3 billion years ago. After that, volcanic eruptions abruptly stopped, with the most recent volcanic activity dating nearly a billion years earlier.

Now, a team of scientists led by Sarah Branden of the Arizona State University in Tempe says small rocky features spotted by NASA's Lunar Reconnaissance Orbiter were laid down by lava not more than 100 million year ago.

On the near side of the moon, the team spotted 70 structures that appear to be lava flows, ranging from 100 meters to 5,000 meters in size. The features show smooth, low and rounded mounds near patches of rough terrain.  

Scientists say the features, which they called mare patches, must be relatively new. The collision between lava and underlying rock should have formed distinct boundary lines moonquakes and other small impacts would have eroded over time.

Scientists estimated the age of the largest patches by counting the craters on them. The technique is based on the idea that old surface will be more heavily pocked with craters than young ones.

Braden says the youngest flow is just 18 million years old. The result suggests the moon did not cool as quickly as scientists once thought.

 "This finding is the kind of science that is literally going to make geologists rewrite the textbooks about the moon," said John Keller, a project scientist at NASA.

Tagsmoon, NASA