Did life’s building blocks form in deep space …?

Graham writes ...

The analysis of samples collected from asteroid Bennu by NASA's OSIRIS-REx mission has yielded significant insights into the origin of the building blocks of life and the conditions prevailing in the early solar system. The first results from the analysis were published recently in early 2025 (1,2,3), suggesting that the biochemistry that makes up our DNA may have occurred off-world, and perhaps even long before the Earth existed.

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Talking more generally, it’s fair to say that we have only the sketchiest of ideas of how life began on Earth, which of course makes it difficult to say much about life elsewhere. One encouraging detail in our search for understanding, however, is how quickly life started on Earth. The earliest fossils are believed to be dated only a few hundreds of millions of years after Earth’s formation and cooling. Given that this is a relatively short period of time for natural selection to produce the first single cell organism, some view this as evidence for panspermia – that is, that life didn’t have its origins on Earth, but started in space. This is not a new idea – it was first proposed in 1972 by Nobel laureate Francis Crick, along with Leslie Orgel, who suggested that life was deliberately brought to Earth by a higher intelligence from another planet! Maybe life didn’t start in space, but the results from the OSIRIS-Rex samples are pointers to the idea that life’s building blocks did.

Bennu, is a carbonaceous asteroid about 500 metres across occupying an Earth orbit-crossing trajectory. Credit: NASA.

There has been much evidence of this point of view, obtained from the analysis of things that have fallen to Earth from space. The most important example of this is the Murchison meteorite which fell in 1969 in Australia – the ‘Shire of Murchison’ is a local government area in Western Australia. This was dated to be about 7 billion years old and contained 90 different amino acids, many more than the 20 which form the basis of life on Earth. Another interesting feature was that the Murchison amino acids came in both left-handed and right-handed varieties (both ‘mirror reflections’), whereas Earth-life amino acids are all left-handed. So, there is clearly significant evidence that not all the amino acids found in the meteorite were due to contamination by the terrestrial environment.

OSIRIS-REx spacecraft during assembly, integration and test in a clean room environment. Credit: NASA.

However, the best way to ensure no contamination is to acquire samples directly from space and store them in an inert environment (usually involving immersion in nitrogen) during transit. There are a number of examples of this, prior to the current OSIRIS-Rex mission, including:
 

• the NASA Stardust spacecraft which collected and returned samples from the coma of Comet Wild,
• the Japanese space agency (JAXA) missions Hayabusa and Hayabusa 2, which were the first to land on asteroids and return samples,
• and the ESA Rosetta mission which landed on a comet and analysed samples in situ.

 
As an interesting aside, the various amino acids comprise different configurations of H, C, N and O atoms, indicating that the nebula from which the solar system formed contained heavy stars that had an explosive ending, thus ensuring the presence of the heavier elements – which in turn ensured that the Sun’s planetary system was ripe in its potential to produce complex life.

Coming back to NASA’s current mission OSIRIS-Rex (the name is a convoluted acronym that I will not repeat here …), the spacecraft landed on asteroid Bennu on 20 October 2020. This object is an ordinary carbonaceous asteroid about 500 metres across, which I have to say looks like a pile of rocky debris held to together by very weak gravity. It occupies an Earth orbit-crossing trajectory, which makes the astrodynamics relatively easy to enable visits. The spacecraft touched down on Bennu and samples were collected and returned to Earth, arriving home in September 2023.

The operational configuration of the OSIRIS-REx spacecraft (computer graphics rendition). Credit: NASA.

​Analysis of the samples indicated the presence of 14 of the 20 amino acids that Earth life harnesses in the production of proteins. However, the major surprise this time was the discovery of all five nucleotide bases G (guanine), C (cytosine), A (adenine), T (thymine) and U (uracil). As you may know these bases comprise the basic ‘alphabet’ of the genetic code, with GCAT occurring in DNA, and the same in RNA but with the base U taking the place of T. This result suggests that the biochemistry that makes up our DNA may have occurred in space, and perhaps in the gaseous nebula long before the creation of the solar system!

Recovery of the sample re-entry capsule in the Utah desert. Credit: NASA.

Other findings in the analysis of the Bennu samples also point to an interesting scenario for the origin of Bennu itself, although some would consider the proposed creation narrative to be somewhat speculative. Various compounds were identified in the analysis, including a surprising richness of ammonia – 12 times higher than in the Murchinson meteorite. This is unexpected as Bennu orbits too close to the Sun to preserve pure ammonia, so this concentration hints at a colder, more distant origin. Also, eleven different minerals were recognised that we know form when brine slowly evaporates. This suggests that the stuff that comprises Bennu was once in an aqueous, salty environment. These, and other clues, led the analysis team at NASA to propose a notional origin account for the asteroid. Briefly, this suggests the formation a protoplanet comprised of rock, metals and ice in the cold outer reaches of the early solar system. As radioactive elements produced in ancient supernovae explosions decayed within, the resulting generation of heat melted some of the ice, creating pockets of mineral-rich liquid water. The chemistry that the Bennu samples reveal suggests that interactions within these ancient waters began the formation of organic molecules. However, in this story, the proposed protoplanet is doomed – a catastrophic collision, perhaps with a similar body, scatters its fragments into space and Bennu, and presumably many other asteroids, formed by the action of gravity from the debris.

A few hundred grams of 'star dust' returned by OSIRIS-REx. Credit: NASA.

This remarkable story, extrapolated from the a few hundred grams of material brought back to Earth by OSIRIS-REx, has credence. Pseudo-panspermia – the idea that the chemistry of life got a kick start from space molecules is supported by the findings of this mission, and other similar spacecraft missions. But does it tell us anything about the origin of life, and the likelihood of life elsewhere? You could ask if a random pile of computer components will inevitably lead to the creation of my laptop. Of course not. The process from the random pile to the laptop is a significant one, requiring the ‘intelligent’ intervention of a skill technician. Similarly, the step from the building blocks of life to the complexity of life as we know it here on Earth could be argued to be of very much greater complexity. So, the process of abiogenesis leading to the diversity of life on Earth remains shrouded in mystery – a humbling and puzzling thought to finish on.
 
The story of this part of OSIRIS-Rex’s mission is given in more detail in a splendid Youtube video created by Astrum which can be viewed here.
 
As always, if you have any thoughts on what I have said in this post, please leave a comment below. Thank you.
 
Graham Swinerd
 
Southampton, UK
March 2025
 
(1)   Life’s ingredients have been found in samples from asteroid Bennu / Science News.
(2)   Abundant ammonia and nitrogen-rich soluble organic matter in samples from asteroid (101955) Bennu / Nature.
(3)   Asteroid Bennu samples found to contain five nitrogenous bases crucial to supporting life / PHYS.ORG.