An asteroid carrying some of the basic building blocks of life has been reported in the journal Nature Astronomy. This finding opens the possibility that life on Earth could have been seeded by chemicals in the cosmos billions of years ago.
“Asteroids provide a time capsule into our home planet’s history, and Bennu’s samples are pivotal in our understanding of what ingredients in our solar system existed before life started on Earth,” Nicky Fox, a NASA official, said in a news release. “NASA’s OSIRIS-REx mission already is rewriting the textbook on what we understand about the beginnings of our solar system.”
Searching for Signs of Life on an Asteroid
Although meteorites, from which asteroids break off from, have been theorized as potential vehicles for life-seeding chemical passengers, analyzing them for its signs has been tricky. Because meteorites pass through the atmosphere, they could pick up moisture, which could then contaminate any sample.
To circumvent that issue, NASA’s OSIRIS-REx mission brought 121.6 grams of sample from asteroid Bennu in September 2023. An international team of scientists analyzed the largest asteroid sample ever returned to Earth and reported that it held organic matter containing ammonia and nitrogen.
Those chemicals are key to building both DNA and RNA, the compounds that give rise to all living things on Earth. The sample also contained evidence of a salty, briny broth where the chemicals could interact and combine.
While the findings do not show, in and of themselves, life on other planets or elsewhere in the universe, it does show that the chemical components were kicking around in space well before life took hold on earth.
Read More: First Samples From 4.5 Billion-Year-Old Asteroid Bennu Could Contain the Seeds of Life
Seeds for Life in Space?
To avoid contamination, the Bennu samples from NASA were handled under nitrogen. Scientists at Kyushu University in Japan analyzed them with high resolution mass spectrometry — a technique used to identify molecules based on their weight and charge. They were especially interested in finding ring-shaped molecules that hold carbon and nitrogen.
In doing so, they struck organic chemistry gold: the sample contained all five nitrogenous bases — adenine, guanine, cytosine, thymine, and uracil — required for building DNA and RNA. They also found xanthine, hypoxanthine, and nicotinic acid (vitamin B3).
In an earlier study of a different asteroid named Ryugu, scientists only detected uracil and nicotinic acid. The other four nucleobases were missing. This could be because the two asteroids picked up different chemical hitchhikers, based on their path and location.
“The difference in abundance and complexity of N-heterocycles between Bennu and Ryugu could reflect the differences in the environment to which these asteroids have been exposed in space,” Toshiki Koga, a researcher with the Japan Agency for Marine-Earth Science and Technology, said in a press release.
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Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
