Sweating The Small Stuff: UArizona Scientists Have Begun To Study Samples From Asteroid Bennu

Sample of Bennu

By Daniel Stolte, University Communications - December 20, 2023

Lately, Tom Zega has been watching his caffeine intake before heading to work.

As a co-investigator of NASA's OSIRIS-REx sample analysis team, Zega is one of a small, but growing, number of scientists who have begun to work on analyzing the pristine extraterrestrial material that the University of Arizona-led mission brought back from Bennu, a near-Earth asteroid thought to be a leftover from the formation of the solar system 4.5 billion years ago.

particles of asteroid sit under an optical microscope

University of Arizona scientists have received 200 milligrams – roughly seven-thousandths of an ounce – of the asteroid Bennu sample for analysis. The small particles pictured here in a concavity slide are observed under an optical microscope. Chris Richards/University Communications

Some particles in the Bennu sample are tiny, barely visible with the unaided eye, and manipulating them requires a very steady hand, said Zega, a professor of planetary science at the UArizona Lunar and Planetary Laboratory.

"I sometimes joke with my students about this – if you've had not enough caffeine or too much, your hand might be somewhat shaky, and the smaller the particle you're working with, the more careful you obviously have to be," he said. Currently, his team at LPL has been allocated about 200 milligrams of sample from Bennu – roughly seven-thousandths of an ounce.

Thanks to the extremely sophisticated equipment at UArizona's Kuiper-Arizona Laboratory for Astromaterials Analysis, they can extract a wealth of information from sample particles down to the nanogram, even picogram level, referring to a billionth or trillionth of a gram, respectively.

The team's main interest lies in how these materials found on the asteroid came to be, and what clues they hold for the origin of the planets, including Earth. A quarter of the sample, which is being curated at NASA's Johnson Space Center in Houston, may be allocated to the members of the mission’s science team, who are spread across the world, while about 70% will be preserved for researchers outside the mission team and for future generations, much like was done with the rocks and soil brought back by the astronauts of the Apollo moon landings, according to Zega.

"NASA preserved a large fraction of those samples for subsequent generations of scientists to look at, and we're still doing groundbreaking science on lunar samples that were brought back in the late 1960s and early 1970s," he said. "Just like the instruments we have now surpass the instruments that they had available at that time, in the future, we'll have instruments that surpass those that we have now."

doctoral student Lucas Smith is seen loading Bennu sample into an electron microscope for analysis.

University of Arizona scientists have received a small portion of the asteroid Bennu sample and analysis has begun in their lab. Here, doctoral student Lucas Smith loads Bennu sample into an electron microscope for analysis. Chris Richards/University Communications

What makes these samples unique and precious is that they were collected at the place they originated, unlike meteorites, which don't make it into the lab until after a long journey to Earth's surface. Meteorites are no longer pristine because they have been exposed to heat during their fall through the atmosphere and weathering on the ground, and they could come from anywhere. They lack, as geologists say, "context."

"With these samples from Bennu, we now have all the contextual information that will enable us to study these materials at the fundamental levels and tell the story of the origins and history of asteroid Bennu," Zega said.

A suite of instruments at the LPL's lab, ranging from optical to electron microscopes allows the team to probe the sample down to the atomic scale, according to Pierre Haenecour, assistant professor of planetary science at LPL and OSIRIS-REx co-investigator.

"We literally can look at single atoms," he said. "We also have a nanoscale secondary ion mass spectrometer, or nanoSIMS for short. It allows us to look at isotopes (different variations of atoms) to understand how each particular component in the sample originated."

Early findings confirm the predictions made about Bennu from the remote survey the OSIRIS-REx spacecraft performed during two years at the asteroid, prior to going in for the sample grab.

As suggested by remote observation of the asteroid, Bennu samples contain copious amounts of water locked up in minerals like clays. The samples are also rich in carbon, nitrogen, sulfur, and phosphorous, according to LPL assistant professor Jessica Barnes, who also is an OSIRIS-REx co-investigator.

"The abundance and isotopic composition of these and other elements will allow us to investigate where in the solar system Bennu’s parent body formed and from which constituents," she said. "The study of organic molecules may help us unravel the chemical processes that turned these simple elements into complex molecules that may have helped start life on Earth and possibly elsewhere."

Training students in cutting-edge science is an important part of the OSIRIS-REx mission. The opportunity to come to the university as a graduate student and spend four or five years working on a sample from a mission as historic as OSIRIS-REx is one that Haenecour said he would have loved.

"It really is a historic opportunity to get involved in and get to do some groundbreaking science," he said.

Doctoral students Zoë Wilbur, Lucas Smith and Iunn Ong discuss sample analysis measurements in front of a computer monitor

Discussing sample analysis measurements in the lab: doctoral students Zoë Wilbur, Lucas Smith and Iunn Ong (front to back). Chris Richards/University Communications

Working with samples of such significance comes with a responsibility that everyone takes seriously, Zega said. Getting everything right is important, and much work goes into the actual measurement itself – calibrating the instruments, taking meticulous notes and laying out the entire thought process before beginning the experiments. Some of the analytical techniques consume sample material in the process, and everyone on the sample analysis team is conscious of that, Zega said.

"I'd be lying if I said I didn't feel pressure when I'm working with one of these samples," he said, adding that when he is working in the lab, he tends to not want an audience. "Sometimes, when I have a collaborator in the lab, and we are working together, I tell them, 'I need you to not talk for the next few minutes, because we're in a really critical step here.'"

Per NASA's science requirement, the OSIRIS-REx mission was tasked with bringing 60 grams, or about two ounces, of sample to Earth. With a confirmed sample mass so far of just over 70 grams, and more sample still waiting to be extracted from the sampling head, the mission has already achieved this milestone, Zega said.

"It is very exciting to have samples from Bennu inside our labs, in the same building where the mission was first conceived by the late LPL Director Mike Drake," said Mark Marley, head of the Department of Planetary Sciences and director of LPL. "I am so proud of our faculty, staff and students who have carried his vision to completion."

The sample analysis team comprises about 200 researchers from all over the world, who coordinate the types of measurements and analyses to ensure that they maximize the science they get from the sample. Hundreds of scientific papers describing analyses of the Bennu sample are expected just in the next couple of years.

According to Haenecour, one 10-microgram particle is enough to produce science for years at a time, and the amount of sample already at UArizona is enough to keep students busy for years.

UArizona's Dante Lauretta is the principal investigator for OSIRIS-REx (formally the Origins, Spectral Interpretation, Resource Identification and Security – Regolith Explorer), and he leads the science team and the mission’s science observation planning and data processing. NASA's Goddard Space Flight Center in Greenbelt, Maryland, provides overall mission management. Lockheed Martin Space in Littleton, Colorado, built the spacecraft. Goddard and KinetX Aerospace were responsible for navigating the OSIRIS-REx spacecraft.

Sweating The Small Stuff: UArizona Scientists Have Begun To Study Samples From Asteroid Bennu - UA News

OSIRIS-REx Sample Analysis Begins at the University of Arizona - YouTube Video