Gravel from space grab upends theories of how life began

epa08758587 An undated handout photo made available by the NASA shows artist's rendering shows OSIRIS-REx spacecraft descending towards asteroid Bennu to collect a sample of the asteroid's surface (issued 20 October 2020). NASA's OSIRIS-REx is ready for touchdown on asteroid Bennu, dubbed 'high-five' manoeuvre, and scheduled for 21 October 2020. EPA-EFE/NASA/Goddard/University of Arizona / HANDOUT HANDOUT EDITORIAL USE ONLY/NO SALES

By Don Pinnock

3 Feb 2025

A scoop of dust from an ancient time capsule hurtling through space has forced a rethink of how inert matter became all that now walks, swims and flies on Earth.

The dusty ball had been hurtling through space undisturbed for billions of years until, in 2020, a Nasa spacecraft pounced on it, grabbed about 120g of its surface and headed back to Earth. It was one of the most audacious missions Nasa has attempted.

What it brought back from Asteroid Bennu, according to research just published in the journal Nature, has upended our theory of how life on Earth began.

The space gravel contains minerals and thousands of organic compounds, including amino acids – the molecules that make up the proteins and nucleobases fundamental to DNA, the building blocks of life.

This doesn’t mean there was life on Bennu, but that millions of asteroids like it could have been delivery vehicles for these vital ingredients as they smacked into Earth and other planets in the Solar System billions of years ago.

Asteroid Bennu. (Photo: Nasa)

A scanning electron microscope image of the sodium carbonate crystalline needles found in samples from Asteroid Bennu. (Image: Rob Wardell, Tim Gooding and Tim McCoy / Smithsonian)

The samples come from Nasa’s $1.2-billion mission OSIRIS-REx – which stands for Origins, Spectral Interpretation, Resource Identification and Security Regolith Explorer. The spacecraft, launched from Florida in 2016, flew to Bennu, collected rocks and dust from the asteroid’s surface in 2020 and landed back on Earth, in Utah, in 2023.

The returned samples were then carefully curated to prevent the decomposition of any delicate materials that would otherwise degrade in Earth’s atmosphere.

They were found to contain the richest bounty of life-friendly extraterrestrial compounds brought to Earth to date. “What makes these results so significant is that we’re finding them in a pristine sample,” says co-author Daniel Glavin, an astrobiologist at Nasa’s Goddard Space Flight Centre in Greenbelt, Maryland.

Material collected from Asteroid Bennu. (Photo: Nature)

As samples from space, meteorites cannot equal such a pristine sample because they’re heated in the atmosphere and contaminated by the planet’s molecules. The Bennu samples were ferried to Earth in a sealed canister, protected from the heat and analysed in a super-clean laboratory under inert gas.

Researchers have found that the space rock is packed full of nitrogen and carbon-rich compounds which include 14 of the 20 amino acids that life on Earth uses to build proteins and all four of the ring-shaped molecules that make up DNA – adenine, guanine, cytosine and thymine.

They also found an array of minerals and ammonia, which is important for biochemical reactions, in the sample.

Scanning electron microscopes revealed the minerals in the Bennu sample. (Image: Nasa)

“But that’s not all they contain,” writes Alexandra Witze in Nature. “The material from Bennu is rich in salts created billions of years ago, probably when watery ponds on Bennu’s parent asteroid evaporated and left behind a crust of minerals.”

Although no signs of life were spotted on the asteroid, those ponds of low-temperature liquid water would have been a good environment to foster the chemistry that could lead to it.

“Having these brines there, along with simple organic stuff, may have kick-started [the process of] making much more complicated and interesting organics like the nucleobases,” says Sara Russell, a mineralogist at the Natural History Museum in London and a co-author of the Nature paper.

From left: Nasa astromaterials curator Francis McCubbin, Nasa sample return capsule science lead Scott Sandford and University of Arizona OSIRIS-REx principal investigator Dante Lauretta collect science data on the sample return capsule from Nasa’s OSIRIS-REx mission shortly after touching down in the Utah desert on 24 September 2023. (Photo: EPA-EFE / Nasa / Keegan Barber)

An artist’s rendering shows the OSIRIS-REx spacecraft descending towards Asteroid Bennu to collect a sample from its surface in a ‘high-five’ manoeuvre scheduled for 21 October 2020. (Photo: EPA-EFE / Nasa / Goddard/ University of Arizona)

Similar brines have been spotted elsewhere in the Solar System, including on the dwarf planet Ceres and on Saturn’s moon Enceladus, according to Julie Castillo-Rogez, a planetary scientist at Nasa’s Jet Propulsion Laboratory in Pasadena, California.

OSIRIS-REx is not the first mission to retrieve samples from an asteroid, but its samples are by far the largest. The Japan Aerospace Exploration Agency has run two sample-return missions to the asteroids Itokawa and Ryugu.

Results from those missions showed a variety of organics and other carbon-rich compounds, based on a few grams of asteroid material. By contrast, OSIRIS-REx brought back about 120g from Bennu – giving scientists more to work with..

“It’s been an absolute joy to be involved in this amazing mission and to collaborate with scientists from around the world to attempt to answer one of the biggest questions asked by humanity: how did life begin,” Russell said.

“Together we have made huge progress in understanding how asteroids like Bennu evolved and how they may have helped make the Earth habitable.” DM

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