New experiments suggest that some of the building blocks of life can survive – and even form complex structures – in concentrated sulphuric acid, raising new possibilities for organic chemistry in the clouds of Venus and on other planets.
Peptides - short chains of amino acids - can remain stable and fold into specific structures in concentrated sulphuric acid, according to research published in the journal PNAS. The findings challenge the assumption that sulphuric acid is necessarily incompatible with complex organic chemistry.
'Is life in concentrated sulphuric acid possible? Most scientists would probably say no. But science is not a democracy. The only thing that matters is following where the data and experimental results lead us, and adjusting our models and hypotheses accordingly', Janusz Pętkowski, PhD, from the Wrocław University of Science and Technology told PAP.
In the paper published in PNAS, a research team – including Pętkowski – presents experimental results showing that peptides made from ordinary Earth-based amino acids can remain stable in concentrated sulphuric acid, provided there is no access to water.
The finding is significant because concentrated sulphuric acid makes up the clouds of Venus. 'And the clouds of Venus are, paradoxically, perhaps one of the most stable environments in the Solar System', Pętkowski says.
He says these clouds, composed of droplets of concentrated (98 percent) sulphuric acid, are persistent and cover the entire planet. The planet's surface is so hot that the acid evaporates before reaching it, a phenomenon known as virga.
'If the clouds are as old as the planet itself, existing for 4.5 billion years, they constitute an incredibly stable environment where organic chemistry might have the time to evolve into something more complex', Pętkowski says.
New possibilities for the search for life therefore extend beyond Venus to other rocky planets where sulphuric acid is the dominant liquid.
Concentrated sulphuric acid is lethal to life on Earth. It destroys the sugars that form the foundation of RNA and DNA (ribose and deoxyribose) and serve as cellular energy sources, and it also cleaves proteins into small fragments.
'However, the fact that acid destroys a peptide and breaks it down into individual amino acids in Earth-like conditions is usually due to the presence of water, which drives protein hydrolysis. The acid merely acts as a catalyst for this breakdown, while water is the actual destructive chemical agent', Pętkowski says. He adds: 'Through ongoing research, we are gradually demonstrating that sulphuric acid is actually an excellent solvent for certain organic compounds. The catch is that the organic chemistry involved would have to differ from that found on Earth'.
Experiments have shown that peptides in sulphuric acid fold into very specific structures. It is the existence of these defined structures that enables the performance of diverse biological functions.
'We expected the sulphuric acid to "cook" the polymer at best, causing the peptide to take the form of a flexible spaghetti-like strand without a stable shape. Instead, the presence of sulphuric acid actually helps the peptides fold into a form where individual segments of the polymer interact with one another. These structures differ from those found in water, yet they are stable', the researcher says.
'At this stage, our peptides do not have a biological function. The next step will be to determine whether they can catalyse chemical reactions, bind metal ions, or interact with other molecules', Pętkowski adds. He believes that this could mark the beginning of a new field of study: biochemistry in sulphuric acid.
'The form life takes on Earth is a result of our planet's specific environmental conditions; it is not a universal template to be applied to every planetary environment in the galaxy. We should not expect Earth-based biochemistry to be directly transferable to Mars or Venus', Pętkowski says.
The results do not prove the existence of life in concentrated sulphuric acid, but they challenge the assumption that such life could not originate or persist there. The researchers point to unconventional solvents, potentially widespread throughout the galaxy, that could create environments capable of sustaining complex organic chemistry.
Ludwika Tomala (PAP)
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