Scientists suspected that elsewhere in the Universe we would find evidence of life right-handedness. Meteorite fragments found here supported that idea. What we have discovered from Bennu, an asteroid, has confirmed that the chemical soup of life can be equally left and right-handed.

Bennu is a carbonaceous asteroid. Carbonaceous means it contains carbon, nitrogen, and organic compounds. Discovered in 1999, it is classified as a Near-Earth Object or NEO that passes by us at its closest a distance half of that between us and the Sun. It does this every six years and circles our star every 1.2 Earth years. Bennu is roughly 490 metres (1,607 feet) in diameter and has the consistency of a hill of gravel, rubble and dirt.

A sample from Bennu, an amount equivalent in weight to a regular bar of sap, was collected by NASA’s Osiris Rex mission when it rendezvoused with the asteroid in 2018. In September 2023, it made it back to Earth. What that sample revealed is changing our understanding of just how complex life could have been on Earth if when it started here it was featured both left and right-handed amino acids.

The Bennu samples reveal ammonia and nitrogen-rich organic compounds and the residue of brine (salt water). These samples are rich in carbon, nitrogen and ammonia and include 14 of the 20 L-amino acids that are found in proteins, the tools of cell life. The samples contain amines, formaldehyde, carboxylic acids, polycyclic aromatic hydrocarbons and N-heterocycles. plus all five nucleobases found in DNA and RNA. The brine contains sodium carbonates, phosphates, sulphates and chlorides (the latter is the salt we sprinkle on french fries).

Astronomers and exobiologists hypothesize that Bennu formed from ejected rubble from a celestial collision to its parent larger body some 4.5 billion years ago. That larger asteroid or proto-planet orbited beyond where Saturn is today. The collision created loose material that gradually gathered together to make Bennu. It also sent the asteroid on a trajectory to the inner Solar System. The speculation about Bennu’s parent is that it resembled a watery body like Saturn’s Enceladus, Jupiter’s Europa, and the dwarf planet Ceres. It is believed that the building blocks of life could have begun to assemble in the saltwater environment of Bennu’s parent and after the collision became permanently frozen in time for us to discover when the Osiris Rex mission brought the samples to us.

The evidence Bennu has revealed indicates an early Solar System filled with organic building blocks for the formation of life. The interesting difference is that the sample building blocks contain both right-handed and left-handed amino acids.

We don’t find right-handed amino acids on Earth. We do on Bennu which suggests that our left-handed world that produced the life we see appears to have happened by the luck of the draw. If Earth had received an equal amount of right-handed organic compounds during its early history, the life that would have emerged could have been far more variable than what we see.

A right-handed “mirror” world of amino acids in abundance is changing our theories on the origins of life. Researchers have synthesized proteins with right-handedness seeking exotic cures for diseases. Now we find that our Solar System was an incubator for right-handed mirrored building blocks so different from the ones responsible for our existence.

This is just one of many mysteries in our Universe. We are made of matter but there is a mirrored opposite called antimatter. Our Universe contains dark matter and dark energy, stuff we are still trying to fathom. We are constructed from L-amino acids, the precursors to DNA, the double-stranded self-replicating nucleic acid. Now we know there are R-amino acids, the mirrored opposite of those responsible for the evolution of life on Earth.

Now, when we search for life elsewhere in the Solar System, whether on or below the surface of Mars, in the high atmosphere of Venus, or on ocean ice moons and dwarf planets, our parameters for discovery have to widen considerably. What will a right-handed-based life form look like? Discoveries await.

The basic molecular construct of our existence, the double-helix we call DNA, it turns out appears to spiral always to the right and not to the left. It doesn’t matter what type of life as we know it…always a right ascending spiral.

In chemistry, non-living molecules don’t discriminate. They mix both right and left-oriented constructs. But not the RNA and DNA, the molecules of life.

Why?

The article appearing in The Astrophysical Journal Letters entitled, “The Chiral Puzzle of Life” was published last month and talks about life having a “chiral bias.” That means the molecules display a specific orientation that cannot be replicated when looking at them in a mirror. The authors, Noemie Globus of New York University and the Center for Computational Astrophysics, and Roger Blandford of Stanford University, in their words, state that “living organisms comprise a system of molecules organized with specific handedness.”

In this case, it suggests a biological bias to right-hand dominance as determined by the RNA and DNA helixes. The helical structures of chained nucleotides rise up always spiraling to the right. This tendency ensures the stability of the genetic code and ensures few errors in replication. One could imagine if there were no chirality, that a percentage of DNA and RNA would display left-handed chirality, and the effect could become quite chaotic during replication.

What caused right-handed RNA and DNA?

The authors speculate that cosmic radiation played a key part. Subatomic particles like prions and muons delivered from the stars and cosmic background radiation may have bombarded long-chain molecules eventually leading to right-handedness becoming inherent to the beginning of life.

Muons, for example, contain enough energy to create a spin polarity when striking a molecule and the authors believe that this along with other potential particles within cosmic radiation became the instruments that led to stable helical structures ascending to the right.

That’s not to say that cosmic particles could equally have delivered left-handed spin producing very different constructs, but would they have led to a self-replication?

One can speculate that in the early Universe when stars and planets were first forming, left and right-handed chirality were equally on display producing all kinds of long-chain molecules of which some could have emerged as self-replicating.

To this day, we find evidence of amino acid molecules not just here on Earth that display left-handed chirality. Might this suggest that left-handedness chemistry constructs don’t lead to life?

The authors hypothesize how life emerged in the early Universe believing that its emergence had a lot to do with the building of long-chain molecules with stable architecture that allowed for rapid decoupling and recoupling of its sub-components, the nucleotides capable of grabbing the base sugars such as adenine, cytosine, guanine, and thymine which could be found nearby in the environment. The bombardment caused by cosmic particles influenced the molecules to spin to the right.

What would these early environments look like? Astrobiologists believe that good candidate environments include meteorites containing nucleotides, hydrothermal vents in the early oceans, volcanoes, and natural wet and dry cycles such as those brought on by tidal movements. All or one could have promoted the growth of long-chain molecules impacted by irradiation to display a polarity bias to right-handed chirality.

In any case, as we further explore the Solar System including asteroids, the Moon, and Mars, we may find biogenic evidence that supports universal right-handedness in life’s molecular origins. The authors of the paper described in this posting predict the likelihood that we will find just that, that all life in the Universe will display the same handedness which does nothing for me as a natural southpaw. But that’s life!

In space, we find evidence of sugars and amino acids floating among the ten sextillion stars of the observable Universe. In endless collisions, these molecular compounds intersect and join together randomly combining to a point where 40 to 100 form chains. These chains with their right-handed and left-handed opposite characteristics can combine to form the dual helical construct that we know of as DNA. It is this natural homochirality that makes self-replication possible and, therefore, life as we know it. If there is other bases for forms of life unknown to us, it may come from combinations of molecules less or more complex than RNA, and DNA. One cannot rule out, then, that our form of DNA-based life is just one of many other life-creating molecules using left and right-handedness attractors to become self-replicating.

The process by which life spontaneously formed in the Universe is called abiogenesis, the organizing of inanimate and inorganic matter into living things. Most of us who haven’t been reared on a religious diet of life’s biblical origin, think abiogenesis happened here on Earth shortly after the planet formed some 4 billion years ago. But it would appear that the conditions for life to form came from space and not from Earth. This origin of life theory is called panspermia, the migration of life to Earth where it found a hospitable environment conducive for it to take root and expand to the more than 7.7 million species that we know of today.

The panspermia theory comes in several flavours. In one or more it is believed that life hitched a ride to Earth either on comets, asteroids, or on rocks blasted from the surface of other planetary bodies that found their way to the early Earth. Another flavour believes life was deliberately planted here by intelligent beings from elsewhere in the Universe with no explanation on how these beings came into existence. This latter version of panspermia theory aligns with those who believe in biblical creation, but in this case life doesn’t come from God, Creator of the Universe.

For those who argue that panspermia came to Earth from another planet, there appears to be evidence that Mars may have been the seed bearer. Mars in the early Solar System may have been a more benign and suitable place for life than Earth. And with Mars’ orbit positioned outside of Earth’s, it was 100 times more likely that a rock seeded with life would travel inward to the surface of our planet rather than the other way around. These panspermia advocates point to evidence gathered from our exploration of Mars and from a meteorite designated ALH84001, identified as from the Red Planet and found in Antarctica in 1984. Some astrobiologists believe the meteorite shows primitive fossils. Others dispute these conclusions. But from rovers on Mars and orbiters above it, we are building a picture of Mars today and in the past. We have detected organic molecules on the planet’s bone-dry surface, the evidence of surface water from the past, and outgassings of methane that are seasonal in nature. All are promising signs of both ancient and possibly even modern microbial life on Mars.

The latest research on the chemistry of RNA adds credence to the theory of life from space well before arriving on Earth. It suggests that the building blocks of sugars, carbon, phosphates and nitrogenous bases, go back to the very earliest days of the Universe during the period of rapid inflation and coinciding with the birth of the first stars and planets, a mix of interstellar chemistry that evolved post-Big-Bang. The research also indicates the importance of homochirality within the chemistry leading to the molecules RNA, DNA, and possibly even other non-Earth biological constructs producing very different forms of life we have yet to discover.