October 15, 2014

Odd features scattered across the moon’s volcanic plains are evidence that volcanoes were still erupting during the Age of Dinosaurs on Earth, according to new data collected by NASA’s Lunar Reconnaissance Orbiter (LRO). The finding overturns the long-held belief that the moon’s volcanic activity ended abruptly about one billion years ago. Instead, small amounts of lava continued to erupt from volcanic vents until less than 100 million years ago. That’s relatively recent–geologically speaking–in the 4.6-billion-year history of the moon.

About 16 percent of the moon’s surface is made up of dark, rocky lowlands called maria (MAHR ee uh), named for their resemblence to bodies of water. (The word maria is Latin for seas. Its singular is mare [MAHR ee].) The maria are cratered landscapes that were partly flooded by lava when volcanoes erupted. The lava then froze, forming rock. Scientists think that the maria formed between about 3 1/2 billion and 1 billion years ago.

In 1971, while orbiting the moon, astronauts on the Apollo 15 mission saw an unusual feature on one mare that scientists later decided was an irregularly shaped caldera (collapsed volcano). Named Ina, the feature was a mix of smooth, rounded, shallow mounds next to patches of rough, blocky terrain. It was also thought to be a one-of-a-kind feature. But in the past five years, scientists from Arizona State University led by astronomer Sarah Braden have discovered 70 similar features, which are now known as irregular mare patches (IMP’s), on the near side of the moon. Although Ina is 1.25 miles (2 kilometers) across, most of the IMP’s are less than one-third mile (500 meters) across at their widest point.

A feature called Maskelyne is one of many newly discovered young volcanic deposits on the Moon. Called irregular mare patches (IMP’s), these areas are thought to be remnants of small basaltic eruptions that occurred much later than the commonly accepted end of lunar volcanism, 1 billion to 1.5 billion years ago. (NASA/GSFC/Arizona State University)

The discovery of the IMP’s suggests that the interior of the moon is warmer than scientists had thought. In particular, Braden said, “the lunar mantle had to remain hot enough to provide magma for the small-scale eruptions that created these unusual young features.” In addition, the moon’s volcanic activity apparently last much longer than previously believed. Some of the IMP’s may be even younger than 100 million years. Ina, for example, may have formed only 10 million years ago.

Additional World Book articles:

• How the Moon Was Born (a Special Report)
• Space exploration (1971) (a Back in Time article)