Decades of institutional experience aided research on solar system’s origins
When NASA’s Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) passed by the Earth in September 2023 and released a sample return capsule full of dust and rocks, it marked the end of a 7-year, 4 billion-mile journey to visit and collect a small piece of an asteroid, but the journey to understanding that material had only just begun.
Scientists at the UC Berkeley Space Sciences Laboratory (SSL), along with colleagues at the Lawrence Berkeley National Laboratory (LBNL) and several other institutions, are delving into material recovered from asteroid Bennu. Building on decades of experience with sample analysis at SSL, their work is refining our understanding of solar system’s evolution and confirming that the ingredients thought necessary for life are plentiful and widespread.
“Because of our experience handling extraterrestrial samples for so many years, we have a critical mass at Space Science Lab to do this kind of research,” said Zack Gainsforth, a research scientist at SSL.
Gainsforth first began studying the composition of the solar system in 2006. He worked in the lab of SSL research physicist and senior space fellow Andrew Westphal who was studying samples of comet dust recovered by the Stardust mission. A self-described lab monkey, Gainsforth performed general lab work and maintained equipment but rapidly grew more and more interested in the science.
Just down the hall, other SSL scientists were working on NASA’s Genesis mission, which collected material from the solar wind and proved pivotal in the development of SSL’s sample recovery and analysis expertise.
Genesis launched in 2001 and passively collected solar wind particles on specially designed molybdenum-coated foils before returning to Earth in 2004 and crashing in the Utah desert when its parachute failed to open. One of the mission’s science goals involved measuring the amount of the radionuclides like Beryllium-10 and Aluminum-26 that collected on the foil.
“It would have been hard to do if the mission had gone right,” said Kees Welten, a research chemist at SSL. “Once it crashed and got exposed to the Utah desert—which has some of the same radionuclides we were looking for in the sample—it was pretty well contaminated.”
Welten was not even on the SSL team originally slated to work with the foils. That team was led by senior space fellow Kunihiko Nishiizumi, but because of the contamination, sample analysis on the Genesis mission became something of an all-hands effort. Scientists, engineers, technicians and machinists all worked together to solve the first major problem. The foils had been crumpled by impact and needed to be carefully and methodically flattened out again. A machinist suggested using guitar tuners.
Nishiizumi and his team, including Staff Research Associate Alex Bixler, developed a special solvent mixture to remove the contamination from the surface of the foils without dissolving the thin layer of molybdenum that holds the captured solar wind particles. Scientists at SSL are still measuring solar wind radionuclides within the foil, but Welten has been busy with asteroids lately.
Until recently, the only asteroid samples studied by scientists were those that had fallen to the Earth as meteorites. Not only were those samples potentially altered by exposure to oxygen and water, but due to the high temperatures of atmospheric deceleration the surviving material may not be representative of the original asteroid. Fragile asteroids, those composed of loosely bound materials like dust and rock, likely wouldn’t survive an encounter with the Earth, so the only way to study them is to go get a piece.
The first pristine asteroid samples were collected by the Japanese space agency JAXA. Hayabusa missions 1 and 2 collected five grams of dust and fragments from near-earth asteroids. Welten and Nishiizumi studied material from both missions, and so it was only natural that their group should be among the first researchers to receive material from OSIRIS-REx which collected over 120 g of regolith from asteroid Bennu.
Welten dissolved the samples into acids and then used accelerator mass spectrometry to measure specific radionuclides produced by interaction with cosmic rays. Beryllium-10 and Aluminum-26, for example, were abundant in the early solar system but have since decayed, so they can be used for radiometric dating of objects in the solar system, similar to the way Carbon-14 is used to date objects on Earth.
Based on their distribution throughout the solar system, it’s thought that objects like Bennu were part of larger parent bodies that broke apart some 1 billion years ago. Welton’s research bolstered previous OSIRIS-REx spacecraft observations, which suggested that the age of the surface material on Bennu is much younger. It varies from tens of millions of years to less than 100,000 years old in some places. It suggests that asteroids are dynamic, ever-changing environments.
Though his own work seeks to answer questions related to these surface processes on asteroids, Welten is also interested in the organic molecules discovered in the Bennu samples.
“Bennu is harboring the building blocks of life. So, if amino acids and organics were delivered to the Earth from asteroid impacts, the next step is figuring out how life started,” said Welten.
Gainsforth is beginning to take those next steps. He worked with Matthew Marcus, a scientist with LBNL, to scan Bennu samples at the Advanced Light Source, a synchrotron that can generate beams of energy all along the electromagnetic spectrum from infrared to X-ray wavelengths. Comparing Bennu sample scans under different wavelengths, Gainsforth was able to understand more about the how the material within Bennu formed and what that tells us about the environment of the early solar system.
Gainsforth and his colleagues described some of the key findings in a study published January 29th in the journal Nature. The parent body that Bennu broke away from must have been large enough and warm enough that liquid water was able to form within it. That water, a brine reminiscent of sea water, evaporated and left salty residues behind.
On the same day that the brines study was published in Nature, the OSIRIS-REx team also published another study in the journal Nature Astronomy in which mass spectrometry revealed that the Bennu samples contained 14 of 20 amino acids found in Earth biology as well as all five nucleobases found in DNA and RNA.
“The fact that we find these prebiotic molecules is very interesting because it shows us that all these different parts of the solar system are all connected,” said Gainsforth. “We know that life emerged on Earth, and I’m hopeful that we might find signs of life elsewhere in the solar system.”
Those potential signs of life might one day be detected by rovers or probes in situ. SSL planetary scientist Anna Butterworth is currently developing an instrument for measuring amino acids and trace organic molecules. The Lab-on-a-chip Organic Analyzer is intended for use on a possible flyby mission to an icy moon like Enceladus. If such future missions detect potential signs of life, samples may still have to be returned to Earth for deeper analysis. NASA’s Perseverance rover has been collecting and storing rock samples on Mars since 2021, but a follow-up mission to collect the samples is still in the planning stages.
Until they can get their hands on a sample from Mars, Enceladus or another extraterrestrial body, Gainsforth and Welten aim to make the most of the samples they already have. They’re confident that the diverse team at SSL will tease out even more exciting finds from Bennu.
“We have an unusual mix of people here including engineers, technicians and machinists that help us come up with solutions that scientists alone might not think of,” said Welten.
