Solar System ‘detectives’ look for clues in leftover ‘crumbs’ from the early Solar System

Solar System 'detectives' look for clues in leftover 'crumbs' from the early Solar System

A focused ion beam scanning electron microscope, capable of drilling a hole in a piece of dust, provided a nanoscopic look at the OSIRIS-REx asteroid sample. (Photo: Mari Cleven/UA Office of Research, Discovery and Innovation)

A magnifying glass simply isn’t enough for the high-tech “sleuths” at the Kuiper Center for Materials Characterization and Imaging at the University of Arizona.

The scientists, who are in the basement of the university’s Kuiper Space Science Building, are working to decipher the stories stored in rocks and dust left over from the early days of the solar system.

The facility has been a resource for public and private science programs, both on and off campus, since 2016. Now, thanks to a four-year, nearly $3 million grant from NASA to support facility operations, scientists will be able to delve into scientific questions than ever before.

“The history of the solar system is encoded in asteroids: the planetary crumbs left over from its birth more than 4.5 billion years ago,” said the facility’s director, Thomas Zega, a UArizona professor of planetary sciences. “The university and NASA are investing a great deal of money and resources to recover a sample from Bennu, a carbonaceous asteroid, and this is the first asteroid sample return mission in NASA history, so it’s important. that we are properly equipped as a scientific team to analyze the sample when it returns.

Co-investigators for the facility include assistant professors of planetary science Jessica Barnes and Pierre Haenecour, as well as Regents Professor of Planetary Science Dante Lauretta, principal investigator for NASA’s OSIRIS-REx mission, which will return a sample of the asteroid. Bennu to Earth later this year.

In addition to asteroid samples, scientists use the facility to analyze meteorites and debris from asteroids and other planetary bodies that fall to Earth. The facility has state-of-the-art instrumentation and is open to users from the campus, as well as from other universities or the private sector. The new grant will allow researchers already receiving funding through NASA to use the payment facility at a reduced rate.

Other NASA programs using the facility include the Interdisciplinary Consortiums for Astrobiology Research, Laboratory Analysis of Returned Samples, and Emerging Worlds. The facility will also serve research efforts on planetary materials returned by sample return missions from other space agencies, such as Japan’s Hayabusa 2, which is the “sister mission” to OSIRIS-REx.

“There is even more sample science to look forward to in the future,” Zega said.

For example, NASA’s Artemis missions will return lunar samples. And UArizona researchers are seeking funding for the CAESAR mission, which would return a sample of a comet.

“The United States has been a world leader in sample science and we want to maintain that, especially here at the University of Arizona,” said University of Arizona President Robert C. Robbins. “Extracting the maximum amount of scientific information from modest samples is not an easy task and requires high-tech instrumentation like the one we have on our campus. I am honored by NASA’s continued faith in our experience, and I look forward to what we will learn.”

scale is everything

The university-led OSIRIS-REx mission was designed to return 60 grams, just over 2 ounces, of material from the surface of asteroid Bennu. The mission team estimates that slightly more than that has been collected, and members of the mission science team, who are spread out across the globe, will receive 25% of the total mass collected. A fraction of the sample will be given to researchers who are not part of the OSIRIS-Rex science team, and the rest will be preserved for future generations of researchers.

“We want to make sure that we can look at the samples at multiple scales, from something you can see in the palm of your hand, down to the atomic level,” Zega said. “To do this, we need extremely sophisticated instrumentation.”

Kuiper’s material imaging and characterization facility includes a focused ion beam scanning electron microscope, transmission electron microscope, electron microprobe lab, and scanning electron microscopes. A NanoSIMS instrument to measure chemical elements in a sample is scheduled to arrive in June.

“There are different types of analyzes that we have to do on samples, and most chemists who study planetary materials specialize in one or more measurement techniques,” Zega said. “We all have different specialties and together our expertise complements and completes the analytical portfolio we wanted to build at the university.”

The tools: from microscopes to atomic probes

The first in a line of sample probing tools is the light microscope, familiar to many and used for centuries. It helps scientists visualize samples several hundred nanometers to micrometers in size, roughly on the scale of bacteria and cells.

“Visible-light microscopes can’t ‘sniff’ out the chemical composition of a sample, but they do give us images that can reveal textures and some information about its microstructure,” Zega said.

“It could also reveal areas in your sample that you might want to focus more on,” he said. “It could give you a sense of spatial relationship, which could tell you a little bit of history to start piecing together some of the history of the show. But it’s not until more sophisticated methods are used that you start to get more of the picture.”

The scanning electron microscope, or SEM, and the electron microprobe are used to analyze samples on a slightly smaller scale. An electron microprobe, also known as an electron probe microanalyzer, is similar to a scanning electron microscope, but offers the added ability to reveal clues about the chemical composition of the sample.

“The microprobe allows us to image and map chemical heterogeneity in a sample in two dimensions at the micrometer scale, less than half the length of an average-sized bacterial cell,” Zega said. “EMS can do the same, although not with the same level of precision. Both can generate images and give us compositional information at the microscale, and both are critical in the analysis of the Bennu sample, for example, because that level of information will tell us where in the sample we might want to investigate further using NanoSIMS or STEM. ”

The NanoSIMS instrument measures the chemical elements in a sample, which is important for understanding the origins of the material. Unlike SEM or microprobe, NanoSIMS can reveal the isotopic composition of a sample. Isotopes are different varieties of chemical elements.

“The isotopic composition of a planetary material can tell us something about its origins and history that elemental information alone can’t,” Zega said. “NanoSIMS also allows us to measure trace elements, which are present in extremely small amounts, on the scale of tens of nanometers.”

The transmission electron microscope operates on the smallest scales, allowing scientists in the Zega lab to see individual atoms.

In 2021, Zega’s team used the tool, combined with quantum mechanics, chemical thermodynamics, and astrophysical modelling, to reconstruct the source journey of a dust grain through the nascent solar system.

“Because humans weren’t around around 4.6 billion years ago to witness all this chemistry, we have to examine the remains and reverse engineer their origins,” Zega said. “That’s what these sophisticated analytical tools allow us to do.”

Decades in the making

“Our meteoric record is incomplete,” Zega said. “Those of us who study meteorites are at the mercy of what falls from the sky; We don’t know exactly where they came from, so we try to piece it together.”

In the early 2010s, Mike Drake, who served as OSIRIS-REx Principal Investigator until his death in 2011, and Lauretta, the mission’s current Principal Investigator, realized that the university needed to build capabilities in science. of samples if he was to take on the mission, according to Zega.

“These guys were visionaries; they knew we needed a sample return mission, and that was an important catalyst for building the facility,” Zega said. “Since then, we have worked hard to recruit the right faculty to run the lab. This is the culmination of 20 years of that effort.”

Astrochemistry, Astrobiology, Astrogeology

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