Extraterrestrial Chemistry with Earthly Possibilities

Who are we? Why are we here? As the Crosby, Stills, Nash & Young song suggests, we are stardust, the result of chemistry occurring in vast clouds of interstellar gas and dust. To better understand how this chemistry might create prebiotic molecules—the seeds of life on Earth and perhaps elsewhere—researchers have been studying the role of low-energy electrons created when cosmic radiation passes through ice particles. Their findings could also shed light on medical and environmental applications on our planet.

Undergraduate student Kennedy Barnes will present the team’s findings at the American Chemical Society (ACS) Fall Meeting. The ACS Fall 2024 meeting is a hybrid meeting that will be held virtually and in person from August 18-22 and includes approximately 10,000 presentations on a range of scientific topics.

“The first detection of molecules in space was by Annie Jump Cannon, a Wellesley College alumna, over a hundred years ago,” says Barnes, who led the study with Rong Wu, another undergraduate, under the guidance of chemistry professor Christopher Arumainayagam and physics professor James Battat. Since Cannon’s discovery, scientists have been interested in how extraterrestrial molecules form.

“Our goal is to explore the relative importance of low-energy electrons versus photons in triggering the chemical reactions responsible for the extraterrestrial synthesis of these prebiotic molecules,” Barnes says.

The few studies that have already probed this question suggested that electrons and photons could catalyze the same reactions. The studies by Barnes and his colleagues, however, suggest that the yield of prebiotic molecules from electrons and low-energy photons may be significantly different in space.

“Our calculations suggest that the number of electrons induced by cosmic rays in cosmic ice could be much greater than the number of photons hitting the ice,” Barnes says. “Therefore, electrons probably play a more important role than photons in the extraterrestrial synthesis of prebiotic molecules.”

In addition to cosmic ice, his research on low-energy electrons and radiation chemistry also has potential applications on Earth. Barnes and his colleagues recently studied the radiolysis of water, finding evidence for the electron-stimulated release of hydrogen peroxide and hydroperoxyl radicals, which destroy stratospheric ozone and act as harmful reactive oxygen species in cells.

“A lot of the results of our research on water radiolysis could be used in medical applications and medical simulations,” Barnes notes, citing the example of using high-energy radiation to treat cancer. “A biochemistry professor once told me that humans are actually bags of water. So other scientists are studying how the low-energy electrons produced in water affect our DNA molecules.”

She also says the team’s findings are applicable to environmental remediation efforts where wastewater is treated with high-energy radiation, which produces large numbers of low-energy electrons that are thought to be responsible for destroying hazardous chemicals.

Getting back to space chemistry, the researchers didn’t limit their efforts to mathematical modeling to try to better understand the synthesis of prebiotic molecules. They also tested their hypothesis by reproducing space conditions in the laboratory. They used an ultra-high vacuum chamber containing an ultra-pure copper substrate that they could cool to ultra-low temperatures, as well as an electron gun that produces low-energy electrons and a laser-driven plasma lamp that produces low-energy photons. The scientists then bombard nanoscale ice films with electrons or photons to see which molecules are produced.

“While we have already focused on how this research is applicable to interstellar submicron ice particles, it is also relevant to cosmic ice on a much larger scale, such as that of Jupiter’s moon Europa, which has an ice shell 20 miles thick,” Barnes says.

So, she suggests, their research will help astronomers understand data from space exploration missions such as NASA’s James Webb Space Telescope and the Europa Clipper, which was originally scheduled to launch in October 2024. Barnes hopes their findings will inspire other researchers to incorporate low-energy electrons into their astrochemistry models that simulate what happens in cosmic ices.

Barnes and his colleagues are also varying the molecular composition of the ice films and studying atom addition reactions to see if low-energy electrons can produce other prebiotic chemistries. This work is being done in collaboration with researchers at the Laboratoire d’étude du rayonnement et de la matière en astrophysique et ambiances in France.

“We’re on the cusp of learning a lot of things, which I think is really exciting and interesting,” Barnes says, touting what she describes as a new space age.