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Lost deep in the flatlands of the Orientale Crater, sucking the last drops from their oxygen tanks, lunar backpackers of the future will thank their lucky stars for Jim Head.

Head's research team has compiled the first comprehensive topographic maps of the Moon's cratered surface. His work — featured on the cover of this week's Science Magazine — provides researchers with a fresh window into the early solar system.

But Head will not be looking to take a celestial day hike anytime soon. Instead, he will use the images to better understand the long history of bombardment on the lunar surface.

Both the Earth and its satellite have been pummeled with meteors, asteroids and comets since their formation. But while geological records of the earliest impacts have been obscured by erosion and tectonic activity on Earth, the lunar surface remains largely intact.

"It sounds silly but we actually have to leave Earth to understand the former years of our own planet," said Head, a professor in the Geological Sciences Department. "That's why we go to the moon … it's right there."

Cratering, the effect of huge impacts, can have far-reaching effects on the formation and evolution of life, he said, pointing to the demise of the dinosaurs following a large impact on the Yucatan peninsula.

"One of those, and we'd be toast," he said. "iPhones wouldn't work — you know, real crisis."

About a year ago, NASA placed in orbit around the moon a Lunar Reconnaissance Orbiter spacecraft with the ability to take highly detailed measurements of surface topography, Head said. The spacecraft shot laser pulses at the moon's surface, measuring the time it took for these pulses to reflect back. Over the past several months, Head's lab worked with researchers from the Massachusetts Institute of Technology and the NASA Goddard Space Flight Center to translate over 2.5 billion of these laser data points into a comprehensive topographic map.

The Orbiter craft will most likely continue to collect data for the next few years, Head said. Topographic maps of the lunar surface existed prior to the craft's mission, but the data was variable and low-resolution.

"The key here is that the data set we have now is completely constant in its characteristics," Head said, pointing to the new detailed, multicolored images. "It's a perfect data set for a global analysis. ... It's incredible."

Researchers identified and mapped over 5,000 craters that are equal to or greater than 20 kilometers in diameter. They also identified the two most heavily cratered, and therefore the oldest, areas. Future lunar voyages — much like the earlier Apollo missions — can now target these regions, collecting samples from the earliest impacts, Head said.

There is no way to directly measure the rate of bombardment from meteors or asteroids, but samples taken from surfaces of a known origin can be dated radiometrically in lab. By comparing the age and density of the impacts, researchers can calculate the rate of bombardment over time and develop an absolute chronology of impacts and impact frequency.

"The rate of bombardment is low now, much lower than it was in the early years," Head said. "But we still we get things falling to the Earth all the time."

It's unclear which of Professor Head's collections he enjoys more: eccentric beer bottles or geological fragments — both of which adorn his office cabinets. But as he shuffles through his meteorite collection, it's obvious that the sparkling rocks tell a story much grander than they initially suggest.

In a broad sense, the new data brings researchers one step closer to the grand question of "how we got to be how we are today," Head said. "If we want to predict the future, knowing the past is really important. ... Was the bombardment history so great that life didn't get started until a certain time — or did these big projectiles bring in life from somewhere else?"

 "These are big issues," he added. "This paper doesn't answer those, but it starts to talk about the earth in its infancy in a way that brings a lot more meaning."



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