Advertisement

If you have an ACS member number, please enter it here so we can link this account to your membership. (optional)

ACS values your privacy. By submitting your information, you are gaining access to C&EN and subscribing to our weekly newsletter. We use the information you provide to make your reading experience better, and we will never sell your data to third party members.

ENJOY UNLIMITED ACCES TO C&EN

Astrochemistry

Compounds critical to life found on ancient asteroid

New analysis of samples from Bennu find amino acids, nucleobases, and sodium minerals on the asteroid

by Fionna Samuels
January 29, 2025

 

A video showing the sampling arm of a spacecraft touching down on the surface of Bennu, blowing the surface material apart with a blast of nitrogen to drive the material into its sample collection head, and backing away.
Credit: NASA Goddard/University of Arizona
OSIRIS-REx uses a blast of nitrogen gas to blow a sample from Bennu back into a collection container.

On Sept. 24, 2023, the OSIRIS-REx spacecraft swung past Earth to drop off precious cargo: 121.6 g of rocks and dust collected from the surface of the asteroid Bennu. Born from the rocky detritus of an impact-shattered larger asteroid, Bennu is a relic of our early solar system. As such, scientists expect it to provide insight into the kinds of life-seeding chemistries that were possible on early Earth. Researchers have now published two complementary papers describing the inorganic and organic composition of small portions of the Bennu sample (Nature 2025, DOI: 10.1038/s41586-024-08495-6; Nat. Astron. 2025, DOI: 10.1038/s41550-024-02472-9).

When Tim McCoy, curator of meteorites at the National Museum of Natural History, and his team began analyzing the minerals in the Bennu sample, they found something unexpected: sodium carbonate. “I worked on meteorites for 35 years,” McCoy says. “I’ve never seen sodium carbonate.”

McCoy turned to the museum’s mineral collection to confirm the finding. In those collection drawers, he found centimeter-scale sodium carbonate crystals that had the same physical characteristics as the micron-scale crystals in the Bennu sample. The earthly samples were evaporites formed in lake beds.

Black-and-white scanning electron microscopy image showing needlelike sodium carbonate crystals. Some small white lumps appear on top of the crystals.
Credit: Rob Wardell, Tim Gooding, and Tim McCoy/Smithsonian
Scanning electron microscopy image of sodium carbonate. The vein of salt is surrounded by clay-rich rock, with small pieces of rock resting on top of the sodium carbonate needles.

Although the chemistry on Bennu’s parent asteroid was almost certainly different from that on Earth, the presence of sodium carbonate crystals gave McCoy an idea of the other kinds of evaporites he should look for in the sample. Ultimately, his team found sodium-bearing phosphates and sulfates, chlorides, and fluorides, all rich in sodium.

The minerals McCoy’s team identified paint a picture of one possible environment present on rocky celestial bodies 4.5 billion years ago. The presence of evaporites means that sodium-rich water once existed on Bennu’s parent, probably in muddy cracks and crevices. The team also found minerals that form only at specific temperatures.

“If you had had a glass of this brine, it would taste like salty, tepid water,” McCoy says. That’s not an attractive drink, he says, but it is an environment amenable to early prebiotic life and one that was present much earlier in the solar system’s history than previously thought.

There is no evidence that life evolved on Bennu or Bennu’s parent body. But the ingredients for life are present on Bennu’s rocky surface. “We saw a whole bunch of amino acids, 14 of which are in proteins,” says NASA astrochemist Jason Dworkin, who coauthored the paper on nitrogen-rich organic in Bennu samples. The researchers also found all 5 nucleobases present in RNA and DNA: guanine, thymine, adenine, cytosine, and uracil. In fact, the team found about 10,000 different nitrogen-containing chemical species. Dworkin’s team and others are working on identifying even more water-soluble and water-insoluble organics.

Finding the precursors to life on a space rock is not new. But Dworkin says it is surprising that all the nonprotein amino acids were present in racemic mixtures. Data collected from meteorites suggested that left-handed chirality was favored in the early solar system, he says. That the samples from Bennu were racemic “throws that theory out,” Dworkin says. “So, there’s more testing to do.” He adds that any researcher is welcome to write a NASA proposal requesting a portion of the Bennu sample.

“The big question still is: How did life form on Earth and does it exist elsewhere?” says Nora Hänni, a chemist and cometary scientist at the University of Bern who was not involved in either study. The results from these studies will inevitably help piece together the answer to that question, she says. But asteroid studies alone aren’t enough. By comparing these data with data from comets and the interstellar medium, the field can get a better sense of what potentially life-bearing chemistry can be considered “normal” in space, Hanni says. The community “needs all the small bits and perspectives actually to study these big questions.”

Article:

This article has been sent to the following recipient:

0 /1 FREE ARTICLES LEFT THIS MONTH Remaining
Chemistry matters. Join us to get the news you need.