Stardust and sugar: Asteroid Bennu sheds new light on life’s origins

When NASA brought home pieces of the asteroid Bennu, scientists hoped the samples might help answer some long-standing questions about how life got its start. They’ve now taken a closer look, and the results are remarkable.

Three new studies report that the samples contain sugars tied to biology, a strange, gum-like material from the solar system’s youth, and more dust from dying stars than anyone expected.

Sugars tied to early life

Sugars linked to biology showed up in the Bennu material. Researchers found ribose, a five-carbon sugar that is needed to build RNA, along with glucose, which is a six-carbon sugar.

Ribose has appeared in a couple of meteorites before, but this is the first time glucose has been seen in material that came straight from an asteroid.

These pieces matter because they tie back to life’s basic toolkit. All five nucleobases used to construct both DNA and RNA, along with phosphates, have already been found in the Bennu samples brought to Earth by OSIRIS-REx.

“The new discovery of ribose means that all of the components to form the molecule RNA are present in Bennu,” said Yoshihiro Furukawa of Tohoku University who led the research.

DNA is absent in the Bennu samples

The team noted that they did not find deoxyribose, which is tied to the production of DNA. That difference hints that ribose may have been more common in the young solar system.

Researchers point to the “RNA world” hypothesis, which suggests that early life may have leaned on RNA, before DNA and proteins took over today’s work.

“Present day life is based on a complex system organized primarily by three types of functional biopolymers: DNA, RNA, and proteins,” explained Furukawa.

“However, early life may have been simpler. RNA is the leading candidate for the first functional biopolymer because it can store genetic information and catalyze many biological reactions.”

The samples also held glucose, one of the most common energy sources for life on Earth. Finding this sugar here means that such energy sources may have been available very early on.

Strange material frozen in time

A second research group found something no one had seen before in astromaterials: a gum-like substance.

The material is packed with nitrogen and oxygen and once had a soft, flexible feel. It hardened long ago, but it still carries signs of its odd past.

The group studied grains rich in carbon, then reinforced and shaved them down until they could inspect them at the molecular scale.

“We knew we had something remarkable the instant the images started to appear on the monitor. It was like nothing we had ever seen, and for months we were consumed by data and theories as we attempted to understand just what it was and how it could have come into existence,” said Zack Gainsforth of UC Berkeley.

This “space gum” seems to have formed as the asteroid’s parent body warmed in its early years. A compound called carbamate likely formed first.

A version of plastic in space

Carbamate usually dissolves in water. In this sample, however, it appears to have polymerized before the asteroid became wet enough to break it down. That process produced tangled chains with unusual chemistry.

Researchers noticed the material could bend slightly before snapping. Sun-like radiation made it brittle, much like outdoor plastics that fade after too many summers.

“Looking at its chemical makeup, we see the same kinds of chemical groups that occur in polyurethane on Earth, making this material from Bennu something akin to a ‘space plastic,'” said Scott Sandford from NASA’s Ames Research Center.

The comparison is only superficial because the structure is far less orderly than polyurethane. It still shows how unexpected this find was.

The team thinks the “gum” could represent one of the earliest chemical steps that helped shape more complex organic matter.

Dust older than the solar system

The third study focused on presolar grains, which form in stars that are older than the Sun. These particles end up locked inside asteroids and hold clues about how the solar system formed.

The Bennu samples had six times the amount of supernova dust seen in any other studied astromaterial. That finding suggests Bennu’s parent body may have formed in a part of the protoplanetary disk filled with debris from dying stars.

Some material inside the samples escaped heavy alteration by fluids. “These fragments retain a higher abundance of organic matter and presolar silicate grains, which are known to be easily destroyed by aqueous alteration in asteroids,” explained Ann Nguyen of NASA’s Johnson Space Center.

“Their preservation in the Bennu samples was a surprise and illustrates that some material escaped alteration in the parent body. Our study reveals the diversity of presolar materials that the parent accreted as it was forming.”

This mix offers a look at the early solar system and how different sources of dust and ice blended together. The untouched pockets of material help researchers trace how Bennu’s parent body grew and changed.

Why Bennu keeps surprising scientists

Bennu has turned out to be one of the most informative asteroids ever studied. Its samples show that complex chemistry didn’t wait for Earth to form.

Sugars that are tied to life, strange polymer-like material, and ancient star dust were already out there. OSIRIS-REx has now brought home a snapshot of that old chemistry. Scientists can piece together what it says about where we came from.

As labs continue working through the material, more surprises may show up. For now, these studies add new layers to a story that stretches back more than four billion years.

The full study was published in the journal Nature Geoscience.

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