Building blocks of life can spring into existence spontaneously when icy comets smash into planets, a study has shown.
A similar process can create amino acids – bits of proteins – when a rocky meteorite strikes an ice-covered world.
The discovery suggests that life could be getting a kick-start anywhere in the universe.
How often the building blocks end up constructing proteins and living organisms is an unanswered question. But the research fills in another piece of the puzzle of life’s origins on Earth.
Scientists believe that when life first emerged, between 4.5 and 3.8 billion years ago, Earth was being bombarded by comets and meteorites.
Dr Zita Martins, from the department of Earth science and engineering at Imperial College London, said: “Our work shows that the basic building blocks of life can be assembled anywhere in the solar system and perhaps beyond.
“However, these building blocks need the right conditions in order for life to flourish.
“Excitingly, our study widens the scope for where these important ingredients may be formed in the solar system.”
Proteins, the giant molecules that form living tissue, are made from chains of amino acids whose assembly is directed by the genetic code. Writing in the journal Nature Geoscience, the scientists show how when a comet – essentially a dirty snowball – hits, it creates a shock wave that generates the molecules needed for amino acids.
Heat from the impact transforms these molecules into the protein building blocks.
The scientists point out that abundant ice on the surfaces of Enceladus and Europa, two moons orbiting Saturn and Jupiter, could provide the perfect conditions for producing amino acids from meteor impacts.
Co-author Dr Mark Price, from the University of Kent, said: “This process demonstrates a very simple mechanism whereby we can go from a mix of simple molecules, such as water and carbon-dioxide ice, to a more complicated molecule, such as an amino acid.
“This is the first step towards life. The next step is to work out how to go from an amino acid to even more complex molecules such as proteins.”
The study involved firing steel projectiles at high velocity into ice mixtures similar to those found in comets.
A large compressed gas gun, housed at the University of Kent, propelled the projectiles at 7.15 kilometres per second.
High temperatures and pressures from the impacts led to the creation of several amino acids, including the important protein components glycine and alanine. Non-protein amino acids were also generated.
For the process to work, raw ingredients such as carbon dioxide, ammonia, methanol and water are needed – these have all been detected on Saturn’s moon Enceladus. The scientists wrote: “We have demonstrated a mechanism for forming complex organics through a simple, high speed impact – no other factors are needed, such as the presence of ultraviolet radiation.”