The Search for Our Cosmic Origins

A photo of Christopher Arumainayagam, professor of chemistry

Photo by Lisa Abitbol

Photo by Lisa Abitbol

For the last year and a half, Christopher Arumainayagam, professor of chemistry, has sought to understand one of the most fundamental questions of all: How did life begin?

In 2016, scientists announced the discovery of the presence of glycine, the simplest amino acid, on a comet. This provided support for a theory called molecular panspermia, which suggests that the molecular building blocks of life were brought to Earth from the cosmos. “If you think about the number of comets, asteroids, and meteorites that pummeled the Earth over millions and millions of years, then you can imagine that a lot of these prebiotic molecules could have been brought to Earth and could have then formed the basis of the evolution of life here,” says Arumainayagam.

But Arumainayagam’s research centers on a question that predates molecular panspermia to the moment when prebiotic molecules like glycine were formed before crashing to Earth. “How were the molecules of life synthesized in outer space?” Arumainayagam asks.

The answer lies in the dark, dense molecular clouds where the prebiotic molecules are produced. Traditional hypotheses suggest that prebiotic molecules are created when photons, the fundamental particles of light, interact with ices in the molecular clouds. But Arumainayagam wonders if different particles, low-energy electrons, might instead—or perhaps additionally—be responsible for the synthesis of these prebiotic molecules.

To investigate this, Arumainayagam and his research students rely on an apparatus that recreates the ultralow-pressure, ultralow-temperature environment of these dark, dense molecular clouds in the lab. The ices, which form around dust grains in the clouds, are replicated with films of water, methanol, or ammonia just 100 molecules thick. These films are then bombarded with photons or low-energy electrons, and the products left behind on the film are analyzed for the existence of prebiotic molecules.

Using a combination of infrared spectroscopy, which identifies the molecules based on their interactions with infrared radiation, and mass spectrometry, which analyzes the identity of the molecules based on fragmentation patterns, Arumainayagam and his students studied the components of the irradiated sample and found that, when interacting with these lab-made cosmic ices, electrons are capable of producing all of the molecules that are traditionally attributed to photons.

While these findings provide support for the possibility that low-energy electrons may have been responsible for the creation of those early prebiotic molecules, they leave many questions unanswered. If both photons and low-energy electrons could have seeded the possibility of life, to which particle do we owe our existence?

For the students working in Arumainayagam’s lab, these lingering questions have made for a humbling research experience. “I realized how much of research is … thinking you have a grip on something and then realizing you don’t. And that’s really fun. It’s a challenge,” says Talia O’Shea ’23.

As for Arumainayagam, this project has allowed him to contribute to a scientific field that is new to him. “A decade ago, I didn’t know anything about astrochemistry. I didn’t even know that such a field existed,” he says.

However, Arumainayagam has always had an interest in astronomy, and seven or eight years ago, he recalls, he began taking an interest in the chemistry of the heavens (which is also the name of a course he teaches at Wellesley). When the pandemic hit in 2020 and his lab was forced to shutter, Arumainayagam decided to turn his attention to some of his burning theoretical, computational, and astrophysical questions about the origins of human life.

But stepping into a new scientific field has proven difficult, even for a seasoned scientist like Arumainayagam. “The physics involved is very challenging. Even though I have an undergraduate degree in chemistry and physics and a graduate degree in chemical physics, I’m going back to reading textbooks on how charged particles interact with matter,” he says. “I’ve gone back to being a student and learning new material.”

Arumainayagam acknowledges that we may never truly know whether photons or electrons were responsible for creating those initial prebiotic molecules that allowed living species to evolve on Earth. But that doesn’t stop him from seeking to understand all that he can about our cosmic origins.

“Ever since the dawn of humanity we have wondered, ‘Where did we come from?’” Arumainayagam says. “I can’t think of anything more fundamental than answering that question.”

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