Researchers offer their most comprehensive assessment to date of the history of water and organic compounds in a sample obtained from a small asteroid called Bennu.

Cold, dark and dry.

For Kim Tait, those three words have long defined conditions for asteroids in our solar system – the minor celestial bodies that are the refuse from planetary formation processes long passed.

Now Dr. Tait, senior curator of mineralogy at the Royal Ontario Museum in Toronto, is re-evaluating the “dry” part of that description.

New results from NASA’s OSIRIS-REx mission, which returned pieces of an asteroid to Earth 16 months ago, show not only that the material’s parent body was once repeatedly inundated with a watery brine, but that this ancient soak-cycle produced the same molecular building blocks that on Earth led to the emergence of life.

“We’re seeing, for the first time, this complete sequence of minerals formed by evaporation of salty, sodium-rich waters outside of Earth,” said Dr. Tait, who is one of more than 70 scientists involved in the work.

Researchers identified salt minerals in the Bennu samples that were deposited as a result of brine evaporation from the asteroid’s parent body. In particular, they found a number of sodium salts, such as the needles of hydrated sodium carbonate highlighted in purple in this false-colored image – salts that could easily have been compromised if the samples had been exposed to water in Earth’s atmosphere. Supplied

In a pair of studies published in the journals Nature and Nature Astronomy, the researchers offer their most comprehensive assessment to date of the history of water and organic compounds in a sample obtained from a small asteroid called Bennu.

Details include the presence of clay and mineral salts, which form when water evaporates and can serve as scaffolding for the production of molecules associated with biological processes on Earth. The water would have been present when the asteroid formed as part of a larger body and where heating by radioactive elements would have supplied the energy to keep water in its liquid form.

“We’ve gone from these black rocks that were sitting in a tray to being able to tell what was happening 4.5 billion years ago, and that’s so exciting for us,” Dr. Tait said.

During a teleconference with reporters on Wednesday, Daniel Glavin, an astrobiologist with NASA’s Goddard Space Flight Center in Greenbelt, Md., and lead author of the second study, described how he and his colleagues extracted compounds by dissolving some of the asteroid sample to make “Bennu tea.”

“We found a really complex soup of organic molecules in this tea,” he said, including 14 out of 20 amino acids used in protein synthesis by living cells on Earth and the five nucleotides that are the building blocks of both DNA and RNA.

A top-down view of the OSIRIS-REx Touch-and-Go-Sample-Acquisition-Mechanism (TAGSAM) head with the lid removed, revealing samples of asteroid Bennu inside. The sample material includes dust and rocks up to about 0.4 in (1 cm) in size. Erika Blumenfeld & Joseph Aebers/Supplied

Previous work with meteorites suggested that evidence of this kind was there to be found among the asteroids that routinely pass near our planet. But the Bennu sample provides a more pristine window into the organic molecules that were present in the early solar system because it is uncontaminated by exposure to Earth’s atmosphere.

The sample also contained a surprise: an equal mix of left- and right-handed versions of the molecules of life. Life on Earth uses only the left-handed form, and molecules found in some meteorites have also shown a bias in that direction. This had led mission scientists to speculate that the left-handed path was preselected in space, with the ingredient then transported to Earth’s surface where life subsequently evolved.

One possible reading of the Bennu results suggests otherwise.

“These findings present a potential pathway for the formation of prebiotic life in the outer solar system, independent of life on Earth, but through a similar mechanism,” said Maikel Rheinstadter, a professor of biophysics at McMaster University in Hamilton, who studies the origins of life and was not involved with the analysis.

A portion of the asteroid Bennu sample delivered to Earth by NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security – Regolith Explorer) mission, set into a microscope slide at the agency’s Goddard Space Flight Center in Greenbelt, Md.. Molly Wasser/NASA/Supplied

If so, the same chemical processes that allowed life to emerge on this planet may have been at work elsewhere and in parallel during the initial stages of the solar system’s formation. This raises the possibility that the chemistry of life is still under way in places that future missions may be able to access, such as the interior of the largest asteroid, Ceres, or under the icy crust of Enceladus, a moon of Saturn that has been observed spraying geysers of salty water from deep cracks in its surface.

One of the implications of the Bennu result is that “it actually might make the search for life easier in some respects,” Dr. Glavin said.

Canadian researchers have a special interest in the asteroid sample. Thanks to Canada’s participation in the OSIRIS-REx mission, the country is entitled to a 1/25 share of the 120 grams of material the spacecraft brought back.

In an interview, Caroline-Emmanuelle Morisset, a planetary scientist with the Canadian Space Agency, said that construction began this week on a laboratory to house Canada’s sample in its pristine state at the agency’s headquarters in St. Hubert, Que.

Dr. Morisset said she could not provide a timeline for the completion of the project. Once the laboratory is complete, researchers will be able to propose investigations using the asteroidal material.

While Canada’s share amounts to just under a teaspoon, Dr. Morisset added that, “scientifically, it’s a lot more than its size.”

OSIRIS-REx returned to Earth in September, 2023, after a seven-year round trip to Bennu. The dark, carbon-rich body turned out to be a rubble pile of loose material only 500 metres across and barely held together by its weak gravity. During the encounter a Canadian-built laser scanner allowed scientists to map the tiny asteroid in three dimensions, helping with the selection of a site where the spacecraft could safely contact the surface and grab a sample.

The canister holding the sample was opened early last year at the Johnson Space Center in Houston, where NASA also maintains its collection of moon rocks and other extraterrestrial materials. Since then, only a portion of the sample has been investigated. About seven grams have also been placed in deep freeze for analysis by future generations of researchers, potentially using techniques that may not yet have been developed.

Ivan Semeniuk
The Globe and Mail, January 29, 2025