Where did life come from? Any answer must grapple with two seemingly paradoxical truths: that life on Earth is abundant and diverse, but Earth is also the only planet in the universe where we’ve confirmed the presence of life.
As such, the search for life’s origins has historically been confined to Earth. The general theory of life’s origins—derived from the famous Miller-Urey experiments—is a familiar one: Billions of years ago a roiling soup of organic molecules on Earth gave rise to the first basic forms of life and sparked an evolutionary trajectory that eventually culminated in apes making iPhones.
In the last few decades, however, sophisticated space technologies have found mounting evidence for panspermia, the theory that the basic building blocks of life caught a ride to Earth on the back of a comet or asteroid. Today, researchers from Université de Sherbrooke in Quebec published a paper in the Journal of Chemical Physics that adds more evidence to the theory of panspermia by demonstrating how the organic molecules that form the building blocks of life can be created in the harsh cosmic environment.
Scientists have known for years that many complex organic molecules that form the building blocks of life are able to exist in space. In 2015, for instance, NASA’s Philae spacecraft noted the presence of 16 different organic molecules on the comet it had been sent to study.
Two years earlier, astronomers had discovered the presence of the molecule that produces one of the four nucleobases of DNA among the ice particles in a giant cloud of interstellar gas 25,000 light years away. Closer to home, scientists working on the Murchison meteorite, which fell to Earth in 1969, found dozens of amino acids and other organic compounds embedded in this hunk of space rock in the last few years.
“Over the last decades, radio astronomers have found all these organic and biological molecules in the interstellar media,” Michael Huels, a researcher at the University of Sherbrooke, told me on the phone. “The question is: How can these molecules form in the rather hostile space environment?”
Read more: Did Life on Earth Come From Outer Space?
Previous research has shown that when simple molecules—such as methane that might be found in icy crusts of Jovian moons, asteroids and coating particles of interstellar dust— are bathed in high-energy radiation, it spurs a chemical reaction that results in the more complex organic molecules that form the building blocks of biotic life.
“The hypothesis is that the ionizing radiation produced by newly formed stars is driving the chemistry in interstellar clouds to produce more complex organic or biological molecules,” Huels told me.
But how exactly does this process unfold?
When high energy radiation interacts with matter it produces a bunch of low-energy secondary electrons in the process. According to Huels, this high energy radiation could be imagined like a bullet burrowing its way through matter, such as the icy film on a grain of cosmic dust. As this radiation (often, but not necessarily in the form of a high-energy photon) bores through the icy film, it ionizes the matter it comes in contact with, knocking off a large number of low-energy electrons in the process.
Huels and his colleagues found that these low-energy electrons have enough energy to induce further chemical reactions in space-based compounds. In fact, these low-energy electrons appear to be a main driver behind the creation of organic molecules in space.
To test this, Huels and his colleagues simulated a space environment. They placed a film of methane ice—methane is an abundant molecule in space—in a vacuum chamber and then bombarded it with low-energy electrons. By studying the way these electrons interacted with the icy film, the researchers found that propylene, ethane, acetylene, and even ethanol were formed in the film from significantly less complex ingredients.
According to Huels, while none of these molecules are strictly necessary for the creation of biotic life, their synthesis from low-energy radiation interacting with ice film is important insofar as it demonstrates the chemical process by which simple molecules are turned into more complex molecules. As the low-energy secondary electrons interact with the icy film, they are essentially breaking up the simple molecules and scattering them around, facilitating “an avalanche” of chemical interactions that result in more complex molecules.
Huels said he hopes to continue research in this direction by adding more complex molecules, such as ammonia or carbon dioxide, into the mix. When exposed to radiation, he said these complex films may give rise to “something more biological and exciting than ethanol.”
Still, the realization that it is actually these secondary, low-energy electrons that do the bulk of the work in the production of organic compounds in space fills in some important knowledge gaps. Although scientists knew organic compounds could exist and survive in space and were aware of the production of secondary, low-energy electrons from ionizing radiation, a detailed understanding of how these factors interact to produce complex organic molecules in space was lacking.
In this respect, the research done by Huels and his colleagues is an important step in understanding the production of molecules that are the basic building blocks of life on Earth—and perhaps throughout the cosmos.
“If radiation and small molecules are universal, then the type of molecules we see in space could possibly be contributing to life elsewhere. It’s something that’s so fundamental, that if it’s happening in our galaxy, the building blocks of life could be synthesized in the Andromeda galaxy, or any other galaxy in the universe.”