Are we alone in the Universe? That’s the question scientists have been asking for centuries. And while it's long gone unanswered, a new discovery could finally unlock the secret of alien life.
It's thanks to the OSIRIS-Rex, a NASA spacecraft that in 2018 landed on an asteroid known as Bennu, over 60 million kilometres (40 million miles) from us. But OSIRIS didn't just touch down on the asteroid. It also collected samples of Bennu and brought them back to Earth in 2023.
This isn't just an impressive feat of engineering, but it meant scientists could examine a ‘one-in-a-million’ asteroid. That's because Bennu isn't just any piece of space rock, but due to its carbon-rich composition and close proximity to Earth, it's effectively a time capsule of the early Solar System.
So what exactly did researchers learn? Well, according to the two papers recently published – one in the journal Nature Astronomy and one in Nature – the findings may force us to rewrite the story of how life started.
What was found on Bennu?
The headline finding is that key building blocks of life were found in the Bennu samples.
Thousands of organic molecular compounds, including 14 of the 20 protein amino acids present in lifeforms on Earth, were identified. Also, 19 non-protein amino acids, rare or absent in known Earth biology, and all five biological nucleobases (the units of genetic code like DNA and RNA) were discovered.
It's true that samples of other asteroids that have fallen to Earth have contained some of these materials. However, this is the richest sample we've ever seen.
But that's not all. Evidence that water was once present on the sample was also found. This came in the form of a variety of salt minerals created during the evaporation of brine from early in the history of Bennu’s parent body. This isn't to say Bennu was covered in water, but just that it was wet or muddy.
So why does a soggy space rock matter? The potential presence of water, combined with the discovery of nucleobases and key amino acids, raises questions about the potential for life outside of Earth.
“We often talk about building blocks of life. As life seems to have originated on Earth, the question is how many of these building blocks for life came from processes on Earth and how many of them came from extraterrestrial material?” Sean McMahon, co-director of the UK Centre for Astrobiology told BBC Science Focus.
These ‘building blocks of life’ are made up of an array of atoms, molecules, cells and biomolecules. That includes the amino acids and nucleobases found on Bennu. While this doesn’t mean these formed into living creatures, it does show how abundant the possibility of life was on the asteroid.
“If these blocks of life on Earth did come from extraterrestrial material, they could have also landed elsewhere in the Solar System. If these building blocks are found in asteroids, there is every chance they were delivered to early Mars for example,” McMahon added.
What this means for life outside Earth
But Bennu doesn’t just give us insights into life on nearby planets. There is no reason to believe these chemical compositions are exclusive to the Milky Way. Other solar systems could be equally rich in these organic molecules which would be good news for life in the Universe.
“In astrobiology, the essential elements for life are nitrogen, phosphorous, carbon, oxygen and sulfur. It seems like they are all there, being organised into interesting and useful compounds for building life,” McMahon says about the Bennu sample.
“If you think about the origin of life as being like a recipe, this is telling us that all the ingredients were there in the cupboard to begin with in the early stages of the solar system.”
But it isn’t just the compounds found on Bennu that give hope for life outside of Earth. As we've seen, the findings of salt minerals hint towards a second key indicator of life: water. Along with the ‘building blocks for life’, water and wet environments are crucial for the development of lifeforms.
These two factors have led researchers to question the potential for prebiotic organic synthesis – the process by which simple organic molecules, the building blocks of life, form in watery environments. Scientists believe that chemical reactions, driven by factors like UV radiation and volcanic activity, allowed water and these organic molecules to interact, eventually leading to the formation of the first organic compounds on Earth.
Bennu, as McMahon suggested, has the ingredients for life, and even the pot of water to throw them in. What it lacked was the energy to start the cooking process.
“Water and organics. Taken together, they build on one another. The third thing needed for life is what is missing, an energy source. Whether that’s sunlight for photosynthesis or sources of chemical energy,” Prof Lewis Dartnell, author and astrobiologist at the University of Westminster told BBC Science Focus.
“We’ve got two out of the three here for life on Bennu. It was short-lived, the water wasn’t around for long and really, life wasn’t going to emerge in this instance.”
We can examine the materials of comets and asteroids through telescopes. We’ve even taken laboratories to comets before, like in the case of the Rosetta space probe which landed on the Comet 67P/Churyumov-Gerasimenko in 2016. But this is one of the clearest signs of life outside Earth we’ve ever had.
There are questions about how far the building blocks of life were synthesised on Bennu – the team currently studying the samples say further investigation is needed.
However, the discovery still shows just how plentiful the ingredients for life might be, not just in nearby orbit but throughout the 96 billion light-year radius that makes up the Universe.
About our experts
Lewis Dartnell is a research scientist, presenter and author. He teaches science communication at the University of Westminster and researches astrobiology and the search for life on Mars.
Sean McMahon is a Reader at the University of Edinburgh, teaching in the School of Physics and Astronomy. He is the co-director of the UK Centre for Astrobiology and an associate editor for the International Journal of Astrobiology.
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