Forty years ago this month, the first astronauts landed on the moon. From a scientific perspective, perhaps the greatest legacy of that first Apollo moon landing, and the five lunar missions that followed, is the rock and dust that the astronauts brought back with them. Scientists have learned a lot from studying the lunar material, and the moon rocks are still giving up their secrets.
Watching on television, it was sometimes hard to make out the grainy black-and-white pictures as astronaut Neil Armstrong climbed down off the lunar module, the LM.
"I'm going to step off the LM now. That's one small step for [a] man; one giant leap for mankind," said Armstrong.
In case anything went wrong and they had to abort the mission, one of Armstrong's first jobs was to grab a sample of material from the surface, describing it as he scooped it up.
This is very interesting. It's a very soft surface, but here and there, where I plug with the contingency sample collector, I run into a very hard surface. But it appears to be a very cohesive material of the same sort. I'll try to get a rock in here. Just a couple."
Moon rocks record of solar system
The six Apollo moon-landing missions collected about 382 kilograms of rock and dust from the moon. And scientists have been studying pieces of it ever since, learning about the origin of the moon, among other things. They concluded that the moon was formed when an object about the size of Mars hit the Earth very early in our planet's history, producing a ring of debris around the Earth, which eventually came together to form the moon.
"So this is a whole new idea that came out of studying the samples, that nobody had a clue about when we went there," says Gary Lofgren, who is the curator of NASA's moon rocks. He says the scientific bounty of the moon rocks includes learning more about the moon, but not just the moon.
"Well I think some of the most significant science is the age of the moon. We've determined that the age of the moon, as we see it is today, is very, very old. And being very old, it records the earliest solar system history. So we aren't just learning about the moon when we study the moon. We're learning about the origin of our solar system and the importance of impact craters in the evolution of our planets."
Clues to Earth's early history
MIT planetary science professor Benjamin Weiss has worked with moon rocks, and he agrees. "It actually gives us clues about the early history of the Earth, which we can't learn about from studying Earth rocks, since there are so few rocks from that period."
Over millions of years on Earth, water erodes rock, continents shift around, volcanoes and earthquakes move mountains. These types of events erase the evidence of Earth's early history. Not so on the moon.
"The moon kind of has a fossil surface from the beginning of the solar system," Weiss said. "And it kind of records the first stages of planetary evolution."
So, for example, it was rocks from the moon that gave Earth scientists important information about the Late Heavy Bombardment, a period billions of years ago when meteors rained down on the moon and Earth and the other inner planets.
"And we learned about that event from studying lunar rocks, which recorded it. So we had no idea that this violent episode in solar system history had even occurred until we brought back samples from the moon."
Still secrets to be discovered
Of the 12 Apollo astronauts who walked on the moon, only one of them was a trained geologist. Harrison Schmitt was on the last moon flight, Apollo 17 in 1972, and he was able to do some instant analysis on samples as he collected them during his first moon walk, noting the condition of small cavities called vesicles in the rock.
"The vesicles are not cleanly [smoothly] spherical. They're spherical, but they have fairly rough outlines. They look as if there's been some recrystallization."
Scientists who want to study the moon rocks have to make a good case for a loan of the priceless specimens. Only about 400 samples are sent out each year for research or teaching. And MIT's Benjamin Weiss says 40 years of studying the moon rocks doesn't mean they've given up all their secrets.
"The lunar rocks keep giving back more and more. And it's because our techniques for analyzing lunar rocks keep getting better and better. So we keep going back to the same lunar samples with the new instrumentation that's developed every year and learning something new."
Benjamin Weiss of MIT is one of the scientists who is still studying the moon rocks, 40 years after the Apollo astronauts collected them and brought them back to Earth.