Challenging long-held assumptions, Aarhus University researchers have demonstrated that the protein building blocks essential for life as we know it can form readily in space. This discovery, appearing in Nature Astronomy, significantly raises the statistical probability of finding extraterrestrial life.
In a modern laboratory at Aarhus University and at an international European facility in Hungary (HUN-REN Atomki), researchers Sergio Ioppolo and Alfred Thomas Hopkinson conduct pioneering experiments. Within a small chamber, the two scientists have mimicked the environment found in giant dust clouds thousands of light-years away. This is no easy feat.
The temperature in these regions is a freezing -260° C. There is almost no pressure, meaning the researchers must constantly pump out gas particles to maintain an ultra-high vacuum. They are simulating these conditions to observe how the remaining particles react to radiation, exactly as they would in a real interstellar environment.
The discovery is significant because it suggests that these essential molecules are far more abundant in the universe than previously believed...
"Eventually, these gas clouds collapse into stars and planets. Bit by bit, these tiny building blocks land on rocky planets within a newly formed solar system. If those planets happen to be in the habitable zone, then there is a real probability that life might emerge," Ioppolo explains...
"These molecules are some of the key building blocks of life," explained co-author Professor Liv Hornekær, the InterCat center leader. "They might actively participate in early prebiotic chemistry, catalyzing further reactions that lead toward life."
"That said, we still don't know exactly how life began. But research like ours shows that many of the complex molecules necessary for life are created naturally in space."...
"We've already discovered that many of the building blocks of life are formed out there, and we'll likely find more in the future."
"We already know from earlier experiments that simple amino acids, like glycine, form in interstellar space. But we were interested in discovering if more complex molecules, like peptides, form naturally on the surface of dust grains before those take part in the formation of stars and planets," says Ioppolo.
Peptides are amino acids bonded together in short chains. When peptides bond with one another, they form proteins, which are essential for life as we know it. Looking for the precursors to proteins is therefore vital in the search for the origin of life, Ioppolo explains.
"We saw that the glycine molecules started reacting with each other to form peptides and water. This indicates that the same process occurs in interstellar space," Hopkinson says. "This is a step toward proteins being created on dust particles, the same materials that later form rocky planets."
Where stars are born
Ioppolo, Hopkinson, and their colleagues at Aarhus University study and mimic the giant dust clouds between the stars because these are the birthplaces of new solar systems.
"We used to think that only very simple molecules could be created in these clouds. The understanding was that more complex molecules formed much later, once the gases had begun coalescing into a disk that eventually becomes a star," Ioppolo explains. "But we have shown that this is clearly not the case."
The discovery is significant because it suggests that these essential molecules are far more abundant in the universe than previously believed.
"Eventually, these gas clouds collapse into stars and planets. Bit by bit, these tiny building blocks land on rocky planets within a newly formed solar system. If those planets happen to be in the habitable zone, then there is a real probability that life might emerge," Ioppolo explains.
"That said, we still don't know exactly how life began. But research like ours shows that many of the complex molecules necessary for life are created naturally in space."
A universal reaction
It might seem like a minor discovery that peptides form naturally from the simplest amino acids in space. However, the chemical process through which amino acids bond is universal. This suggests that the same reaction likely occurs with other, more complex amino acids as well, explains Hopkinson.
"All types of amino acids bond into peptides through the same reaction. It is therefore very likely that other peptides naturally form in interstellar space as well," says Hopkinson. "We haven't looked into this yet, but we are likely to do so in the future."
Amino acids and peptides are not the only building blocks essential to life; membranes, nucleobases, and nucleotides are necessary as well. Whether these also form naturally in space remains unknown, but Ioppolo, Hopkinson, and their colleagues at the Center for Interstellar Catalysis are working hard to find out.
"These molecules are some of the key building blocks of life," explained co-author Professor Liv Hornekær, the InterCat center leader. "They might actively participate in early prebiotic chemistry, catalyzing further reactions that lead toward life."
"There's still a lot to be discovered, but our research team is working on answering as many of these basic questions as possible," Ioppolo says. "We've already discovered that many of the building blocks of life are formed out there, and we'll likely find more in the future."
