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Fifty years of demystifying the moon

CSE Professor Emeritus Robert Pepin reminisces about the U of M’s involvement in NASA’s Apollo missions

Robert “Bob” Pepin will never forget what it felt like to study the first rocks ever to be brought back from the moon. 

“They look like things you might just pick up on the sidewalk,” he recalled. “But they were genuine lunar samples, and lunar samples are kind of a big deal.”

The former University of Minnesota physics professor is now retired. But in 1969, Pepin was one of the first scientists in the world to study samples from the Earth's lunar satellite, along with fellow College of Science and Engineering (CSE) professor and geochemist V. Rama Murthy.

In doing so, both researchers learned a great deal about the chemical composition of the sun, and eventually the origins of the moon.

Planting the American flag on the moon on July 20, 1969, may have been one giant leap for mankind, but it was an even bigger deal for science. As if to emphasize this, when Pepin and Murthy arrived back in Minnesota with precious lunar cargo in hand from the Houston Space Center, they were met by a police escort and asked to wait at the back of the plane while the other passengers got off.

Robert Pepin_2019
CSE Professor Emeritus Robert Pepin today, with a photo taken during the 1969 lunar rock exhibit at the University of Minnesota. He was involved with NASA's space programs for 50 years. Credit: Olivia Hultgren

Of course, Pepin laughs about the situation now.

“To this day, the flight attendants probably think we were dangerous criminals being escorted off the plane by the police," Pepin said.

Before being studied, the lunar samples, made up of several chips of moon rock and plastic vials of finely ground gray powder, were displayed at the University’s Space Science Center, which is now Shepherd Laboratories—with two armed guards to watch over.

A chain of discoveries

While the late Professor Murthy focused more on using radioactive dating methods to determine the age of the moon rocks, Pepin studied the abundance of helium, argon, krypton, neon and xenon in the samples using a vacuum furnace.

“We had a unique facility in Minnesota,” he said. “We could analyze samples that were smaller than what anybody else in the world could do at that time.”

During the first few years, the researchers learned more about the sun than the moon. Due to a phenomenon called the solar wind, the heat of the Earth’s sun had deposited signatures of its chemical make-up onto the lunar soil, allowing researchers to determine its chemical composition. 

“It’s important because the assumption is: if we can determine the chemical composition of the sun, we can determine the chemical composition of the material from which the original solar system was made,” Pepin said. 

This discovery opened the door for scientists to theorize how our solar system was formed and how it has changed in the past millions of years. 

“Our atmosphere today looks nothing like this original stuff,” he explained. “So, what happened? How come? That’s the puzzle.”

After analyzing lunar samples from the rest of NASA’s Apollo missions, Pepin, Murthy, and the rest of NASA’s principal investigators elicited a revolutionary theory of how the moon was formed: it came from the Earth.

The theory states that when Earth was still young, a Mars-sized projectile collided with it, causing molten rock from Earth and the impactor to fan out around Earth. Eventually, that material melded together to form the moon. 

Through distinguishing the age of rocks from both the moon and Earth, Murthy contributed to the now widely-accepted view that the two are fairly close in age and that the Earth is about 4.5 billion years old. 

Robert Pepin and V. Rama Murthy
University professors Robert Pepin and V. Rama Murthy became media stars as two of the first scientists in the world to study lunar rocks. Credit: Robert Pepin

Pepin harbors nothing but praise for his former colleague. Professor Emeritus V. Rama Murthy passed away in 2012. His lunar findings further cemented his legacy in the field of geophysics and geochemistry.

“I remember in these press conferences being absolutely astonished at how communicative and polite and interesting Rama was to the people doing the interviewing,” Pepin said. “He was quite a remarkable guy.”

Old rocks, new findings

Although the six NASA missions brought back more than 800 pounds of lunar material, only about two pounds of it has ever been studied. The rest is kept sealed by NASA in a vault in hopes that future scientists and modern-day instruments could reveal more. But, last year NASA announced that it was going back to the moon—and dipping into its remaining stash of moon rocks as a part of its Apollo Next Generation Sample Analysis program. 

That’s where University of Minnesota researcher and geochemist Jed Mosenfelder comes in. 

Mosenfelder, who manages the Experimental Petrology Lab in the College of Science and Engineering’s Department of Earth and Environmental Sciences, is part of a team of scientists from across the United States who will unseal and examine the mineral contents of these samples.

His job is to look for tiny particles of hydrogen, with a long-term goal of figuring out whether water was present on the moon during its formation. 

“The question is: During that formation, were there volatile elements that came in from other parts of the solar system?” Mosenfelder explained. “Was there also water that dissolved on the moon?”

Mosenfelder said one of his favorite aspects of studying the moon is pushing the limits of his technique, using a secondary ion mass spectrometer. 

“Maybe a decade or two decades ago, people couldn’t do what I’m doing because the technique wasn’t developed yet,” he said. “We’re looking at such tiny, tiny amounts of an element, and it’s hard to measure.”

While this research will unveil information about the moon’s history and beginnings, these new rocks could also reveal whether there still is water on the moon—a hotly debated topic for many years.

Mosenfelder has been working with moon samples since 2015, although not previously untouched ones such as these.

“There’s a weird buzz to working on rocks from the moon,” he said. “It blows my mind when I think of some guy out there who ripped up this thing in space and brought it back.”

Fly me to the moon, or to mission control at least

Despite all the time Pepin spent studying lunar samples, the CSE professor's involvement in the Apollo program didn’t stop with the rocks. He lent a hand with everything from astronaut training to NASA’s Sample Allocation Committee, or the folks who decided who got to study pieces of the moon.

“One of the requests we got was for two pounds of lunar samples because this guy wanted to drive a robotic truck over it and see what happened,” he said. “We turned that one down.” 

For Apollo missions 14-17, Pepin joined the big leagues at NASA’s mission control center in Houston, Texas. His job was to advise astronauts on what samples to collect while on the moon. His most infamous contribution? A dietary change for future astronauts.  

During Apollo 15, while the astronauts were drilling into the moon’s surface, the drill core became stuck in the lunar soil. Pepin was tasked with deciding whether they should try to remove the core or abandon it. 

“This was the only decision I personally had to make in mission control,” he said. “Finally, I said, ‘It’s an important sample, keep trying.’”

One of the astronauts developed arrhythmia while removing the drill, which resulted in astronauts on the next mission getting their orange juice doused with potassium to avoid heart issues. The astronauts on Apollo 16 weren’t too happy with that addition. Pepin was privy to their thoughts when they accidentally left their mission control speaker on.

“They said things about oranges that I cannot repeat,” Pepin said with a laugh.

Beyond his time in mission control, Pepin spent three years as director of the Lunar Science Institute in Houston, Texas, and later became a co-investigator for Curiosity, the robotic rover currently exploring Mars. Now, long after setting eyes on those first samples from the moon, Pepin still works on scientific papers from the data he collected prior to retirement. 

And his fascination with the moon continues, 50 years after Neil Armstrong and Buzz Aldrin set foot on Earth’s most peculiar satellite. 

Story by Olivia Hultgren