Physics Professor Has Paper Published in Prestigious Journal

Cal State San Marcos physics professor Gerardo Dominguez has had a paper published in a prestigious scientific journal that marks the latest chapter in his career-long research into isotope chemistry and its possible influence on the origins of the solar system.

Dominguez’s paper, titled “Mass-Independent Oxygen Isotope Fractionation Driven by Energetic-Particle Irradiation of Icy Solids,” was published last week in the Proceedings of the National Academy of Sciences (PNAS). The PNAS is a peer-reviewed multidisciplinary journal that has existed since 1915 and is one of the most cited scientific journals in the world.

“It means a huge deal to me,” Dominguez said. “It’s very difficult to get a paper accepted into PNAS. I’m proud of this paper and its findings because they have broad implications for a number of fields, including physical chemistry, astrophysics and planetary science. It’s a major contribution to science. In some ways, it represents a synthesis of my graduate school training and postdoctoral work.”

Dominguez’s research team – which included CSUSM undergraduate students, CSUSM physics lecturer Caroline Caplan and scientists from UCLA and Washington University in St. Louis – discovered that energetic particles striking icy mineral surfaces can change the proportions of different types of oxygen atoms in an unusual pattern. These changes, known as mass-independent oxygen isotope fractionation (MIF), have usually been linked to chemical reactions involving gases, particularly those that form ozone. The new experiments show that similar changes can occur when energetic particles strike solid minerals covered in water ice, even at extremely cold temperatures of 10 kelvin (about minus-263 degrees Celsius).

Dominguez and his fellow researchers used specialized laboratory equipment to recreate some of the extremely cold, low-pressure conditions found in space. They placed water ice on surfaces made of silica and alumina, then bombarded the samples with energetic electrons.

To see how the oxygen isotopes changed, they used a technique at UCLA called secondary ion mass spectrometry (SIMS), which measures the isotopic composition of materials. The results showed that the relative amounts of oxygen isotopes changed significantly. The researchers also discovered that radiation could alter a mineral's surface in ways that lasted even after the radiation stopped. If water ice later came into contact with the altered surface, additional chemical reactions could take place that would not normally occur at 10 kelvin.

“One of the great mysteries in planetary science is why the sun and the rocky planets, including Earth, have different proportions of oxygen isotopes,” Dominguez said. “Oxygen comes in several forms, called isotopes, and their relative abundances act like chemical fingerprints that tell us about the history and origins of planetary materials. Like ‘CSI’ for the solar system.

“Our research has discovered a previously unrecognized process that can alter these fingerprints. We demonstrated that when energetic particles strike tiny mineral grains coated with ice, they can trigger chemical reactions that change the relative abundances of oxygen isotopes in the solids. These are conditions similar to those found in the cold environments of interstellar space where the raw materials that eventually formed our solar system originated. This process could also be relevant for understanding the permanently shadowed regions of the moon where water ice has been detected and are also exposed to galactic cosmic rays.”

What makes the discovery particularly exciting, Dominguez said, is that the effects of radiation can persist long after the exposure itself. In essence, dust grains can retain a chemical memory of their exposure to radiation, which can influence their chemistry when they later encounter water ice.

“The real-world significance is that we have identified a new piece of the puzzle of how Earth and the other planets may have acquired their oxygen isotopic compositions,” he said. “Our findings suggest that processes occurring on microscopic dust grains, potentially millions of years before the planets formed, may have helped establish the chemical signatures we measure in meteorites and planetary materials today.

“This research does not yet tell us how important this process was in forming our particular solar system, but it provides a new mechanism that scientists can now investigate to better understand the origins of planets and better understand astronomical observations that detect isotopes of oxygen.”

One of the CSUSM students who participated in the early stages of the research project recently completed a doctoral program at UCLA. The recipient of the President’s Outstanding Graduate Award in 2020, Lauren Tafla now works at NASA’s Johnson Space Center in Houston.

Dominguez has been a professor at CSUSM since 2011. He first conceived of the experiment that led to his PNAS paper 10 years ago, and his interest in mass-independent isotope chemistry dates back to his years as a postdoctoral fellow at UC San Diego almost two decades ago.