Scientists using high-resolution images from cameras on NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft estimate geologically recent volcanic eruptions on the moon’s surface. The study, published today in Nature Geoscience, challenges previous models of lunar thermal evolution.

Scientists at Arizona State University’s School of Earth and Space Exploration say eruptions may have occurred as recently as 50 million years ago, current with the Earth’s cretaceous period. This raises the possibility that more may come in the future.

Eruptions are thought to have peaked on the moon’s near side around three billion years ago, waning out around a billion years ago. This is evident in the geological features of the basaltic mare plains, the dark areas visible from Earth that appear to give the moon the appearance of a man’s face.

Geologists say that the moon has seen much smaller, but widespread eruptions of basaltic lava during the last 50 million years, a geologically recent period. These features, which are not visible from Earth, average less than one-third of a mile across.

Scientist studied images of these features from pictures taken from NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft, which provided resolution between 50 and 200 centimeters per pixel—the sharpest pictures of the lunar surface ever taken, Science reports. The team used a model that relies on correlating the number of craters in an area to its age, with more heavily-cratered areas.

Previous thought had assumed a much cooler moon, one long devoid of any volcanic activity. If these surface features are indicative of recent eruptions, the moon may still be warmer than thought, its decline in core temperature a much slower process. This activity is generated in the crust of the moon’s near side, which is a couple hundred degrees warmer than crust on the far-side.

“Such late-stage eruptions suggest a long decline of lunar volcanism and constrain models of the Moon’s thermal evolution,” Arizona State’s Mark Robinson reasons in the report.