I watched the first manned lunar landing in 1969 on a low-
definition television in a glass-enclosed back porch. As I followed the grainy images of Neil Armstrong stepping onto the dusty lunar soil, I could see the moon peeking through tree branches overhead. It looked as it always had, but somehow different. That sudden change in perspective was the whole point of the Apollo 11 landing. It wasn’t a scientific mission. It was an exercise of Cold War hubris intended to burnish America’s image and humble its Communist rival. With Armstrong’s one small first step, though, the space race was over, and the entire Apollo program rapidly wound down. The 1971 image of Alan Shepard hammering a golf ball across the moonscape with a six iron during Apollo 14 remains etched in the popular mind as the end of lunar exploration.
But ask a planetary scientist and you will get a different spin. Jeffrey Taylor of the University of Hawaii says it was the final Apollo missions of 1972 that propelled lunar science and transformed our understanding of the moon. The stars weren’t the guys in the space suits but the 842 pounds of rocks the astronauts brought back to Earth before their program was disbanded.
Even as Apollo was coming to an end, those lunar rocks were catapulting lunar research into new territory, settling centuries-old questions about the moon’s geology and history. One debate revolved around the nature of the moon’s “seas,” or maria—the smooth, broad, dark-colored regions that create the “man in the moon” markings. Researchers put a sliver of moon rock under a microscope, and the issue was settled instantly. The maria are solidified lava flows, vast outpourings of basaltic rock from around three and a half billion years ago. Then in the mid-1970s, planetary scientist William K. Hartmann and a few others proposed that the moon was formed by the collision of a Mars-size planet with the Earth. That dramatic idea encountered skepticism until an analysis of the lunar rocks showed that they have the same mix of oxygen isotopes as rocks found on Earth, strongly suggesting a shared origin. The giant impact theory is now the widely accepted explanation of the moon’s origin.
Forty years later, humans still haven’t made it back to the moon. But moon rocks—some of them analyzed with ever more powerful spectroscopy to reveal chemical composition here on Earth and some by robotic craft on the lunar surface itself—are still full of surprises. “The moon is telling us things that we had no idea were happening,” says Brian Day, an astronomer at NASA’s Ames Research Center in California. “It’s a much more complex and dynamic story than we had believed.”
Getting the story straight has taken a long time. Large portions of the lunar surface remained unseen until 1990, when NASA’s Galileo probe flew by the moon on its way to Jupiter, snapping detailed pictures of the lunar north pole with sensors that captured different wavelengths of light. That quick photo shoot revealed polar highlands up close for the first time.
Then in 1994, NASA launched the Clementine spacecraft to orbit the moon and map its surface. The agency split the mission’s costs with the Ballistic Missile Defense Organization (better known as the driving force behind the Star Wars defense system), which wanted to find out how high-tech sensors and other components would perform during an extended period in space. Despite its divided mandate, Clementine made a stunning discovery: The permanently shaded south pole of the moon seemed to be covered with water ice.
The renewed focus on the moon has reached a pinnacle with a trifecta of revelations released in the past year. In the first of these, geologist Lars Borg of the Lawrence Livermore National Laboratory in California has raised fresh questions about how the moon was born and what happened right after.
Reporting in Nature last August, Borg described detailed new studies of a moon rock weighing about six-tenths of an ounce. He chose this one from the huge Apollo collection because it was considered one of the oldest rocks on the moon. The best date for the moon’s age is 4.55 billion years. But when Borg, working with colleagues in Denmark and Washington, D.C., finished measuring radioactive isotopes in the rock, they pegged its age at 4.36 to 4.359 billion years.