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ASU research on Apollo samples refines lunar impact history


February 12, 2015

It’s been more than 40 years since astronauts returned the last Apollo samples from the moon, and since then those samples have undergone some of the most extensive and comprehensive analysis of any geological collection.

A team led by Arizona State University researchers has now refined the timeline of meteorite impacts on the moon through a pioneering application of laser microprobe technology to Apollo 17 samples. Apollo sample Download Full Image

Impact cratering is the most ubiquitous geologic process affecting the solid surfaces of planetary bodies in the solar system. The moon’s scarred surface serves as a record of meteorite bombardment that spans much of solar system history.

Developing an absolute chronology of lunar impact events is of particular interest because the moon is an important proxy for understanding the early bombardment history of Earth, which has been largely erased by plate tectonics and erosion, and because we can use the lunar impact record to infer the ages of other cratered surfaces in the inner solar system.

Researchers in ASU’s Group 18 Laboratories, headed by professor Kip Hodges, used an ultraviolet laser microprobe, attached to a high-sensitivity mass spectrometer, to analyze argon isotopes in samples returned by Apollo 17. While the technique has been applied to a large number of problems in Earth’s geochronology, this is the first time it has been applied to samples from the Apollo archive.

The samples analyzed by the ASU team are known as lunar impact melt breccias – mash-ups of glass, rock and crystal fragments that were created by impact events on the moon’s surface.

When a meteor strikes another planetary body, the impact produces very large amounts of energy – some of which goes into shock, heating and melting the target rocks. These extreme conditions can "restart the clock" for material melted during impact. As a result, the absolute ages of lunar craters are primarily determined through isotope geochronology of components of the target rocks that were shocked and heated to the point of melting, and which have since solidified.

However, lunar rocks may have experienced multiple impact events over the course of billions of years of bombardment, potentially complicating attempts to date samples and relate the results to the ages of particular impact structures.

Conventional wisdom holds that the largest impact basins on the moon were responsible for generating the vast majority of impact melts, and therefore nearly all of the samples dated must be related to the formation of those basins.

While it is true that enormous quantities of impact melt are generated by basin-scale impact events, recent images taken by the Lunar Reconnaissance Orbiter Camera confirm that even small craters with diameters on the order of 100 meters can generate impact melts. The team’s findings have important implications for this particular observation. The results are published in the inaugural issue of the American Association for the Advancement of Science’s newest journal, Science Advances, on Feb. 12.

“One of the samples we analyzed, 77115, records evidence for only one impact event, which may or may not be related to a basin-forming impact event. In contrast, we found that the other sample, 73217, preserves evidence for at least three impact events occurring over several hundred million years, not all of which can be related to basin-scale impacts,” says Cameron Mercer, lead author of the paper and a graduate student in ASU’s School of Earth and Space Exploration.

Sample 77115, collected by astronauts Gene Cernan and Harrison Schmitt at Station 7 during their third and final moonwalk, records a single melt-forming event about 3.83 billion years ago. Sample 73217, retrieved at Station 3 during the astronauts’ second moonwalk, preserves evidence for at least three distinct impact melt-forming events occurring between 3.81 billion years ago and 3.27 billion years ago. The findings suggest that a single small sample can preserve multiple generations of melt products created by impact events over the course of billions of years.

“Our results emphasize the need for care in how we analyze samples in the context of impact dating, particularly for those samples that appear to have complex, polygenetic origins. This applies to both the samples that we currently have in our lunar and meteoritic collections, as well as samples that we recover during future human and robotic space exploration missions in the inner solar system,” says Mercer.

 

Nikki Cassis

marketing and communications director, School of Earth and Space Exploration

ASU signs partnership to educate Peruvian teachers


February 13, 2015

For the last 20 years, Violeta Calderon has been an English teacher to high school-aged students in her home country of Peru.

Now, Calderon, who is 49, is spending seven weeks in a classroom at Arizona State University’s West campus – this time as a student. Peruvian students in class Peruvian English teachers in class on ASU's West campus. ASU gave each a Chromebook to help complete their studies. Download Full Image

She’s part of an extensive English teacher training program for 235 Peruvian public high school teachers that is run through the American English and Culture Program at ASU.

“I wanted to come here to do this – for me it’s a blessing,” Calderon said. “To come to another country, to come to the United States, to have this special program because I want to improve. Not only my listening, but speaking, so I have an opportunity to practice my English all the time.”

In the program, which started Jan. 19, Peruvian teachers like Calderon are improving their English language communication skills and their teaching methodology so they can go back to Peru and elevate the level of English education in their entire region.

The teachers were granted a full scholarship to attend this program at ASU through PRONABEC, the continuing education and scholarship granting arm of the Peruvian Ministry of Education.

Their arrival at ASU comes as a new agreement was signed between the university and the Peruvian government.

“I am enormously proud to partner with Arizona State University and the Government of Peru to transform English teaching in Peru,” said Brian A Nichols, America’s Ambassador to Peru. “ASU’s historic agreement to train hundreds of Peruvian teachers in English education will improve the educational outcomes of thousands of students around the country.”

The Peruvian government selected ASU out of a prestigious group of American universities to host the teachers. They are the largest group Peru has ever sent abroad for teacher training, signaling the country’s excitement about the ASU partnership.

“We were pleased to be selected from other top U.S. universities to deliver this robust training program for public high school teachers,” said Robert E. Page, Jr., university provost. “ASU and the Ministry of Education in Peru share a common commitment to academic excellence and to social inclusion.”

The Peruvian teachers will not only be improving their own English skills, but they will be learning how to better teach English when they get back home, and how to pass along their new skills to their colleagues.

“We put them through a demanding program while they’re here, but it is one that they will leave with tremendous new talents to share in their communities,” said Shane Dixon, educational lead of ASU’s Peruvian teacher training program.

The Ministry of Education in Peru wants to send around 4,000 English teachers abroad to improve their ability to teach at home. The government believes that English proficiency among its people will improve its economic success.

"It is gratifying to know that our teachers will specialize in such an important issue as the English language, because knowledge and mastery of English is key to strengthening the ability of young Peruvians to thrive in the global economy," said the executive director of PRONABEC, Raul Choque.

Of the 235 participants, 70 are from Lima, the capital of Peru, while the remainder of the group is from other parts of the country.

Martin Laban, 46, teaches in a female-only public high school in Piura, 15 hours by bus from Lima.

“The first week was a culture shock but then I adapted to this and ASU,” Laban said. “I love this kind of culture and the experience I’m getting here.”

Laban said every day in Arizona is a new experience for him.

“I hope to learn many interesting things, to take them to my school and put in practice, especially strategies and techniques,” Laban said. “I am totally convinced that they are going to be important for my students.”

Aside from the teacher training part of the program, the students are getting to experience the culture of ASU and the American Southwest.

Participants attended the Martin Luther King Day “I Have A Dream” speech re-enactment on ASU’s west campus in January, went on a trip to the Grand Canyon and attended a Super Bowl viewing party.

Additionally, the participants will visit local schools around the Valley; hear from guest speakers from Mary Lou Fulton Teacher’s College, as well as speakers from the community; attend an ASU Men’s Basketball game; attend the Renaissance Festival in Tempe; and go to the Celebrate Peru Day on the Tempe campus to make a presentation about Peru culture to a wider audience.

"The Peruvian government is making a series of strategic investments in education,” said Julia Rosen, associate vice provost. “We hope that this program is just the first of many to come."

Written by Samantha Pell, ASU News